@@ -502,7 +502,7 @@ func (e *historyEngineImpl) StartWorkflowExecution(
 		startRequest,
 	)
 	if err != nil {
-		return nil, serviceerror.NewUnavailable("Failed to add workflow execution started event.")
+		return nil, err
 	}
 
 	// Generate first workflow task event if not child WF and no first workflow task backoff
// The MIT License
//
// Copyright (c) 2020 Temporal Technologies Inc.  All rights reserved.
//
// Copyright (c) 2020 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package history

import (
	"bytes"
	"context"
	"fmt"
	"sync/atomic"
	"time"

	"github.com/pborman/uuid"
	commonpb "go.temporal.io/api/common/v1"
	enumspb "go.temporal.io/api/enums/v1"
	historypb "go.temporal.io/api/history/v1"
	querypb "go.temporal.io/api/query/v1"
	"go.temporal.io/api/serviceerror"
	taskqueuepb "go.temporal.io/api/taskqueue/v1"
	workflowpb "go.temporal.io/api/workflow/v1"
	"go.temporal.io/api/workflowservice/v1"
	sdkclient "go.temporal.io/sdk/client"

	"go.temporal.io/server/common/persistence/visibility"

	enumsspb "go.temporal.io/server/api/enums/v1"
	"go.temporal.io/server/api/historyservice/v1"
	"go.temporal.io/server/api/matchingservice/v1"
	persistencespb "go.temporal.io/server/api/persistence/v1"
	replicationspb "go.temporal.io/server/api/replication/v1"
	workflowspb "go.temporal.io/server/api/workflow/v1"
	"go.temporal.io/server/client/admin"
	"go.temporal.io/server/client/history"
	"go.temporal.io/server/common"
	"go.temporal.io/server/common/clock"
	"go.temporal.io/server/common/cluster"
	"go.temporal.io/server/common/definition"
	"go.temporal.io/server/common/failure"
	"go.temporal.io/server/common/log"
	"go.temporal.io/server/common/log/tag"
	"go.temporal.io/server/common/metrics"
	"go.temporal.io/server/common/namespace"
	"go.temporal.io/server/common/persistence"
	"go.temporal.io/server/common/persistence/versionhistory"
	"go.temporal.io/server/common/primitives/timestamp"
	"go.temporal.io/server/common/rpc/interceptor"
	"go.temporal.io/server/common/searchattribute"
	serviceerrors "go.temporal.io/server/common/serviceerror"
	"go.temporal.io/server/common/xdc"
	"go.temporal.io/server/service/history/configs"
	"go.temporal.io/server/service/history/consts"
	"go.temporal.io/server/service/history/events"
	"go.temporal.io/server/service/history/shard"
	"go.temporal.io/server/service/history/workflow"

	"go.temporal.io/server/service/worker/archiver"
)

const (
	conditionalRetryCount                     = 5
	activityCancellationMsgActivityNotStarted = "ACTIVITY_ID_NOT_STARTED"
)

type (
	historyEngineImpl struct {
		status                    int32
		currentClusterName        string
		shard                     shard.Context
		timeSource                clock.TimeSource
		workflowTaskHandler       workflowTaskHandlerCallbacks
		clusterMetadata           cluster.Metadata
		executionManager          persistence.ExecutionManager
		visibilityMgr             visibility.VisibilityManager
		txProcessor               transferQueueProcessor
		timerProcessor            timerQueueProcessor
		visibilityProcessor       visibilityQueueProcessor
		nDCReplicator             nDCHistoryReplicator
		nDCActivityReplicator     nDCActivityReplicator
		replicatorProcessor       *replicatorQueueProcessorImpl
		eventNotifier             events.Notifier
		tokenSerializer           common.TaskTokenSerializer
		historyCache              *workflow.Cache
		metricsClient             metrics.Client
		logger                    log.Logger
		throttledLogger           log.Logger
		config                    *configs.Config
		archivalClient            archiver.Client
		workflowResetter          workflowResetter
		queueTaskProcessor        queueTaskProcessor
		replicationTaskProcessors []ReplicationTaskProcessor
		publicClient              sdkclient.Client
		eventsReapplier           nDCEventsReapplier
		matchingClient            matchingservice.MatchingServiceClient
		rawMatchingClient         matchingservice.MatchingServiceClient
		replicationDLQHandler     replicationDLQHandler
		searchAttributesValidator *searchattribute.Validator
		searchAttributesMapper    searchattribute.Mapper
	}
)

// NewEngineWithShardContext creates an instance of history engine
func NewEngineWithShardContext(
	shard shard.Context,
	visibilityMgr visibility.VisibilityManager,
	matching matchingservice.MatchingServiceClient,
	historyClient historyservice.HistoryServiceClient,
	publicClient sdkclient.Client,
	eventNotifier events.Notifier,
	config *configs.Config,
	replicationTaskFetchers ReplicationTaskFetchers,
	rawMatchingClient matchingservice.MatchingServiceClient,
	queueTaskProcessor queueTaskProcessor,
) *historyEngineImpl {
	currentClusterName := shard.GetService().GetClusterMetadata().GetCurrentClusterName()

	logger := shard.GetLogger()
	executionManager := shard.GetExecutionManager()
	historyCache := workflow.NewCache(shard)
	historyEngImpl := &historyEngineImpl{
		status:             common.DaemonStatusInitialized,
		currentClusterName: currentClusterName,
		shard:              shard,
		clusterMetadata:    shard.GetClusterMetadata(),
		timeSource:         shard.GetTimeSource(),
		executionManager:   executionManager,
		visibilityMgr:      visibilityMgr,
		tokenSerializer:    common.NewProtoTaskTokenSerializer(),
		historyCache:       historyCache,
		logger:             log.With(logger, tag.ComponentHistoryEngine),
		throttledLogger:    log.With(shard.GetThrottledLogger(), tag.ComponentHistoryEngine),
		metricsClient:      shard.GetMetricsClient(),
		eventNotifier:      eventNotifier,
		config:             config,
		archivalClient: archiver.NewClient(
			shard.GetMetricsClient(),
			logger,
			publicClient,
			shard.GetConfig().NumArchiveSystemWorkflows,
			shard.GetConfig().ArchiveRequestRPS,
			shard.GetService().GetArchiverProvider(),
		),
		publicClient:       publicClient,
		matchingClient:     matching,
		rawMatchingClient:  rawMatchingClient,
		queueTaskProcessor: queueTaskProcessor,
	}

	historyEngImpl.txProcessor = newTransferQueueProcessor(shard, historyEngImpl, visibilityMgr, matching, historyClient, queueTaskProcessor, logger)
	historyEngImpl.timerProcessor = newTimerQueueProcessor(shard, historyEngImpl, matching, queueTaskProcessor, logger)
	historyEngImpl.visibilityProcessor = newVisibilityQueueProcessor(shard, historyEngImpl, visibilityMgr, matching, historyClient, queueTaskProcessor, logger)
	historyEngImpl.eventsReapplier = newNDCEventsReapplier(shard.GetMetricsClient(), logger)

	if shard.GetClusterMetadata().IsGlobalNamespaceEnabled() {
		historyEngImpl.replicatorProcessor = newReplicatorQueueProcessor(
			shard,
			historyEngImpl.historyCache,
			executionManager,
			logger,
		)
		historyEngImpl.nDCReplicator = newNDCHistoryReplicator(
			shard,
			historyCache,
			historyEngImpl.eventsReapplier,
			logger,
		)
		historyEngImpl.nDCActivityReplicator = newNDCActivityReplicator(
			shard,
			historyCache,
			logger,
		)
	}
	historyEngImpl.workflowResetter = newWorkflowResetter(
		shard,
		historyCache,
		logger,
	)

	historyEngImpl.searchAttributesValidator = searchattribute.NewValidator(
		shard.GetService().GetSearchAttributesProvider(),
		shard.GetService().GetSearchAttributesMapper(),
		config.SearchAttributesNumberOfKeysLimit,
		config.SearchAttributesSizeOfValueLimit,
		config.SearchAttributesTotalSizeLimit,
	)

	historyEngImpl.searchAttributesMapper = shard.GetService().GetSearchAttributesMapper()

	historyEngImpl.workflowTaskHandler = newWorkflowTaskHandlerCallback(historyEngImpl)

	var replicationTaskProcessors []ReplicationTaskProcessor
	replicationTaskExecutors := make(map[string]replicationTaskExecutor)
	for _, replicationTaskFetcher := range replicationTaskFetchers.GetFetchers() {
		sourceCluster := replicationTaskFetcher.GetSourceCluster()
		// Intentionally use the raw client to create its own retry policy
		adminClient := shard.GetService().GetClientBean().GetRemoteAdminClient(sourceCluster)
		adminRetryableClient := admin.NewRetryableClient(
			adminClient,
			common.CreateReplicationServiceBusyRetryPolicy(),
			common.IsResourceExhausted,
		)
		// Intentionally use the raw client to create its own retry policy
		historyClient := shard.GetService().GetClientBean().GetHistoryClient()
		historyRetryableClient := history.NewRetryableClient(
			historyClient,
			common.CreateReplicationServiceBusyRetryPolicy(),
			common.IsResourceExhausted,
		)
		nDCHistoryResender := xdc.NewNDCHistoryResender(
			shard.GetNamespaceCache(),
			adminRetryableClient,
			func(ctx context.Context, request *historyservice.ReplicateEventsV2Request) error {
				_, err := historyRetryableClient.ReplicateEventsV2(ctx, request)
				return err
			},
			shard.GetService().GetPayloadSerializer(),
			shard.GetConfig().StandbyTaskReReplicationContextTimeout,
			shard.GetLogger(),
		)
		replicationTaskExecutor := newReplicationTaskExecutor(
			sourceCluster,
			shard,
			shard.GetNamespaceCache(),
			nDCHistoryResender,
			historyEngImpl,
			shard.GetMetricsClient(),
			shard.GetLogger(),
		)
		replicationTaskExecutors[sourceCluster] = replicationTaskExecutor

		replicationTaskProcessor := NewReplicationTaskProcessor(
			shard,
			historyEngImpl,
			config,
			shard.GetMetricsClient(),
			replicationTaskFetcher,
			replicationTaskExecutor,
		)
		replicationTaskProcessors = append(replicationTaskProcessors, replicationTaskProcessor)
	}
	historyEngImpl.replicationTaskProcessors = replicationTaskProcessors
	replicationMessageHandler := newReplicationDLQHandler(shard, replicationTaskExecutors)
	historyEngImpl.replicationDLQHandler = replicationMessageHandler

	shard.SetEngine(historyEngImpl)
	return historyEngImpl
}

// Start will spin up all the components needed to start serving this shard.
// Make sure all the components are loaded lazily so start can return immediately.  This is important because
// ShardController calls start sequentially for all the shards for a given host during startup.
func (e *historyEngineImpl) Start() {
	if !atomic.CompareAndSwapInt32(
		&e.status,
		common.DaemonStatusInitialized,
		common.DaemonStatusStarted,
	) {
		return
	}

	e.logger.Info("", tag.LifeCycleStarting)
	defer e.logger.Info("", tag.LifeCycleStarted)

	e.txProcessor.Start()
	e.timerProcessor.Start()
	if e.visibilityProcessor != nil {
		e.visibilityProcessor.Start()
	}

	// failover callback will try to create a failover queue processor to scan all inflight tasks
	// if domain needs to be failovered. However, in the multicursor queue logic, the scan range
	// can't be retrieved before the processor is started. If failover callback is registered
	// before queue processor is started, it may result in a deadline as to create the failover queue,
	// queue processor need to be started.
	e.registerNamespaceFailoverCallback()

	for _, replicationTaskProcessor := range e.replicationTaskProcessors {
		replicationTaskProcessor.Start()
	}
}

// Stop the service.
func (e *historyEngineImpl) Stop() {
	if !atomic.CompareAndSwapInt32(
		&e.status,
		common.DaemonStatusStarted,
		common.DaemonStatusStopped,
	) {
		return
	}

	e.logger.Info("", tag.LifeCycleStopping)
	defer e.logger.Info("", tag.LifeCycleStopped)

	e.txProcessor.Stop()
	e.timerProcessor.Stop()
	if e.visibilityProcessor != nil {
		e.visibilityProcessor.Stop()
	}

	for _, replicationTaskProcessor := range e.replicationTaskProcessors {
		replicationTaskProcessor.Stop()
	}

	if e.queueTaskProcessor != nil {
		e.queueTaskProcessor.StopShardProcessor(e.shard)
	}

	// unset the failover callback
	e.shard.GetNamespaceCache().UnregisterNamespaceChangeCallback(e.shard.GetShardID())
}

func (e *historyEngineImpl) registerNamespaceFailoverCallback() {

	// NOTE: READ BEFORE MODIFICATION
	//
	// Tasks, e.g. transfer tasks and timer tasks, are created when holding the shard lock
	// meaning tasks -> release of shard lock
	//
	// Namespace change notification follows the following steps, order matters
	// 1. lock all task processing.
	// 2. namespace changes visible to everyone (Note: lock of task processing prevents task processing logic seeing the namespace changes).
	// 3. failover min and max task levels are calculated, then update to shard.
	// 4. failover start & task processing unlock & shard namespace version notification update. (order does not matter for this discussion)
	//
	// The above guarantees that task created during the failover will be processed.
	// If the task is created after namespace change:
	// 		then active processor will handle it. (simple case)
	// If the task is created before namespace change:
	//		task -> release of shard lock
	//		failover min / max task levels calculated & updated to shard (using shard lock) -> failover start
	// above 2 guarantees that failover start is after persistence of the task.

	failoverPredicate := func(shardNotificationVersion int64, nextNamespace *namespace.CacheEntry, action func()) {
		namespaceFailoverNotificationVersion := nextNamespace.GetFailoverNotificationVersion()
		namespaceActiveCluster := nextNamespace.GetReplicationConfig().ActiveClusterName

		if nextNamespace.IsGlobalNamespace() &&
			namespaceFailoverNotificationVersion >= shardNotificationVersion &&
			namespaceActiveCluster == e.currentClusterName {
			action()
		}
	}

	// first set the failover callback
	e.shard.GetNamespaceCache().RegisterNamespaceChangeCallback(
		e.shard.GetShardID(),
		e.shard.GetNamespaceNotificationVersion(),
		func() {
			e.txProcessor.LockTaskProcessing()
			e.timerProcessor.LockTaskProcessing()
		},
		func(prevNamespaces []*namespace.CacheEntry, nextNamespaces []*namespace.CacheEntry) {
			defer func() {
				e.txProcessor.UnlockTaskPrrocessing()
				e.timerProcessor.UnlockTaskProcessing()
			}()

			if len(nextNamespaces) == 0 {
				return
			}

			shardNotificationVersion := e.shard.GetNamespaceNotificationVersion()
			failoverNamespaceIDs := map[string]struct{}{}

			for _, nextNamespace := range nextNamespaces {
				failoverPredicate(shardNotificationVersion, nextNamespace, func() {
					failoverNamespaceIDs[nextNamespace.GetInfo().Id] = struct{}{}
				})
			}

			if len(failoverNamespaceIDs) > 0 {
				e.logger.Info("Namespace Failover Start.", tag.WorkflowNamespaceIDs(failoverNamespaceIDs))

				e.txProcessor.FailoverNamespace(failoverNamespaceIDs)
				e.timerProcessor.FailoverNamespace(failoverNamespaceIDs)

				now := e.shard.GetTimeSource().Now()
				// the fake tasks will not be actually used, we just need to make sure
				// its length > 0 and has correct timestamp, to trigger a db scan
				fakeWorkflowTask := []persistence.Task{&persistence.WorkflowTask{}}
				fakeWorkflowTaskTimeoutTask := []persistence.Task{&persistence.WorkflowTaskTimeoutTask{VisibilityTimestamp: now}}
				e.txProcessor.NotifyNewTask(e.currentClusterName, fakeWorkflowTask)
				e.timerProcessor.NotifyNewTimers(e.currentClusterName, fakeWorkflowTaskTimeoutTask)
			}

			// nolint:errcheck
			e.shard.UpdateNamespaceNotificationVersion(nextNamespaces[len(nextNamespaces)-1].GetNotificationVersion() + 1)
		},
	)
}

func createMutableState(
	shard shard.Context,
	namespaceEntry *namespace.CacheEntry,
	runID string,
) (workflow.MutableState, error) {

	var newMutableState workflow.MutableState
	// version history applies to both local and global namespace
	newMutableState = workflow.NewMutableState(
		shard,
		shard.GetEventsCache(),
		shard.GetLogger(),
		namespaceEntry,
		shard.GetTimeSource().Now(),
	)

	if err := newMutableState.SetHistoryTree(runID); err != nil {
		return nil, err
	}

	return newMutableState, nil
}

func (e *historyEngineImpl) generateFirstWorkflowTask(
	mutableState workflow.MutableState,
	parentInfo *workflowspb.ParentExecutionInfo,
	startEvent *historypb.HistoryEvent,
) error {

	if parentInfo == nil {
		// WorkflowTask is only created when it is not a Child Workflow and no backoff is needed
		if err := mutableState.AddFirstWorkflowTaskScheduled(
			startEvent,
		); err != nil {
			return err
		}
	}
	return nil
}

// StartWorkflowExecution starts a workflow execution
func (e *historyEngineImpl) StartWorkflowExecution(
	ctx context.Context,
	startRequest *historyservice.StartWorkflowExecutionRequest,
) (resp *historyservice.StartWorkflowExecutionResponse, retError error) {

	namespaceEntry, err := e.getActiveNamespaceEntry(startRequest.GetNamespaceId())
	if err != nil {
		return nil, err
	}
	namespace := namespaceEntry.GetInfo().Name
	namespaceID := namespaceEntry.GetInfo().Id

	request := startRequest.StartRequest
	e.overrideStartWorkflowExecutionRequest(request, metrics.HistoryStartWorkflowExecutionScope)
	err = e.validateStartWorkflowExecutionRequest(ctx, request, namespace, "StartWorkflowExecution")
	if err != nil {
		return nil, err
	}

	err = searchattribute.SubstituteAliases(e.searchAttributesMapper, request.GetSearchAttributes(), namespace)
	if err != nil {
		return nil, err
	}

	workflowID := request.GetWorkflowId()
	// grab the current context as a Lock, nothing more
	_, currentRelease, err := e.historyCache.GetOrCreateCurrentWorkflowExecution(
		ctx,
		namespaceID,
		workflowID,
	)
	if err != nil {
		return nil, err
	}
	defer func() { currentRelease(retError) }()

	execution := commonpb.WorkflowExecution{
		WorkflowId: workflowID,
		RunId:      uuid.New(),
	}
	clusterMetadata := e.shard.GetService().GetClusterMetadata()
	mutableState, err := createMutableState(e.shard, namespaceEntry, execution.GetRunId())
	if err != nil {
		return nil, err
	}

	startEvent, err := mutableState.AddWorkflowExecutionStartedEvent(
		execution,
		startRequest,
	)
	if err != nil {
		return nil, serviceerror.NewUnavailable("Failed to add workflow execution started event.")
	}

	// Generate first workflow task event if not child WF and no first workflow task backoff
	if err := e.generateFirstWorkflowTask(
		mutableState,
		startRequest.ParentExecutionInfo,
		startEvent,
	); err != nil {
		return nil, err
	}

	weContext := workflow.NewContext(namespaceID, execution, e.shard, e.logger)

	now := e.timeSource.Now()
	newWorkflow, newWorkflowEventsSeq, err := mutableState.CloseTransactionAsSnapshot(
		now,
		workflow.TransactionPolicyActive,
	)
	if err != nil {
		return nil, err
	}
	if len(newWorkflowEventsSeq) != 1 {
		return nil, serviceerror.NewUnavailable("unable to create 1st event batch")
	}

	// create as brand new
	createMode := persistence.CreateWorkflowModeBrandNew
	prevRunID := ""
	prevLastWriteVersion := int64(0)
	err = weContext.CreateWorkflowExecution(
		now,
		createMode,
		prevRunID,
		prevLastWriteVersion,
		mutableState,
		newWorkflow,
		newWorkflowEventsSeq,
	)
	if err != nil {
		if t, ok := err.(*persistence.CurrentWorkflowConditionFailedError); ok {
			if t.RequestID == request.GetRequestId() {
				return &historyservice.StartWorkflowExecutionResponse{
					RunId: t.RunID,
				}, nil
				// delete history is expected here because duplicate start request will create history with different rid
			}

			if mutableState.GetCurrentVersion() < t.LastWriteVersion {
				return nil, serviceerror.NewNamespaceNotActive(
					request.GetNamespace(),
					clusterMetadata.GetCurrentClusterName(),
					clusterMetadata.ClusterNameForFailoverVersion(t.LastWriteVersion),
				)
			}

			// create as ID reuse
			createMode = persistence.CreateWorkflowModeWorkflowIDReuse
			prevRunID = t.RunID
			prevLastWriteVersion = t.LastWriteVersion
			if err = e.applyWorkflowIDReusePolicyHelper(
				t.RequestID,
				prevRunID,
				t.State,
				t.Status,
				namespaceID,
				execution,
				startRequest.StartRequest.GetWorkflowIdReusePolicy(),
			); err != nil {
				return nil, err
			}
			err = weContext.CreateWorkflowExecution(
				now,
				createMode,
				prevRunID,
				prevLastWriteVersion,
				mutableState,
				newWorkflow,
				newWorkflowEventsSeq,
			)
		}
	}

	if err != nil {
		return nil, err
	}
	return &historyservice.StartWorkflowExecutionResponse{
		RunId: execution.GetRunId(),
	}, nil
}

// GetMutableState retrieves the mutable state of the workflow execution
func (e *historyEngineImpl) GetMutableState(
	ctx context.Context,
	request *historyservice.GetMutableStateRequest,
) (*historyservice.GetMutableStateResponse, error) {

	return e.getMutableStateOrPolling(ctx, request)
}

// PollMutableState retrieves the mutable state of the workflow execution with long polling
func (e *historyEngineImpl) PollMutableState(
	ctx context.Context,
	request *historyservice.PollMutableStateRequest,
) (*historyservice.PollMutableStateResponse, error) {

	response, err := e.getMutableStateOrPolling(ctx, &historyservice.GetMutableStateRequest{
		NamespaceId:         request.GetNamespaceId(),
		Execution:           request.Execution,
		ExpectedNextEventId: request.ExpectedNextEventId,
		CurrentBranchToken:  request.CurrentBranchToken,
	})

	if err != nil {
		return nil, err
	}
	return &historyservice.PollMutableStateResponse{
		Execution:                             response.Execution,
		WorkflowType:                          response.WorkflowType,
		NextEventId:                           response.NextEventId,
		PreviousStartedEventId:                response.PreviousStartedEventId,
		LastFirstEventId:                      response.LastFirstEventId,
		LastFirstEventTxnId:                   response.LastFirstEventTxnId,
		TaskQueue:                             response.TaskQueue,
		StickyTaskQueue:                       response.StickyTaskQueue,
		StickyTaskQueueScheduleToStartTimeout: response.StickyTaskQueueScheduleToStartTimeout,
		CurrentBranchToken:                    response.CurrentBranchToken,
		VersionHistories:                      response.VersionHistories,
		WorkflowState:                         response.WorkflowState,
		WorkflowStatus:                        response.WorkflowStatus,
	}, nil
}

func (e *historyEngineImpl) getMutableStateOrPolling(
	ctx context.Context,
	request *historyservice.GetMutableStateRequest,
) (*historyservice.GetMutableStateResponse, error) {

	namespaceID, err := validateNamespaceUUID(request.GetNamespaceId())
	if err != nil {
		return nil, err
	}
	execution := commonpb.WorkflowExecution{
		WorkflowId: request.Execution.WorkflowId,
		RunId:      request.Execution.RunId,
	}
	response, err := e.getMutableState(ctx, namespaceID, execution)
	if err != nil {
		return nil, err
	}
	if request.CurrentBranchToken == nil {
		request.CurrentBranchToken = response.CurrentBranchToken
	}
	if !bytes.Equal(request.CurrentBranchToken, response.CurrentBranchToken) {
		return nil, serviceerrors.NewCurrentBranchChanged(response.CurrentBranchToken, request.CurrentBranchToken)
	}
	// set the run id in case query the current running workflow
	execution.RunId = response.Execution.RunId

	// expectedNextEventID is 0 when caller want to get the current next event ID without blocking
	expectedNextEventID := common.FirstEventID
	if request.ExpectedNextEventId != common.EmptyEventID {
		expectedNextEventID = request.GetExpectedNextEventId()
	}

	// if caller decide to long poll on workflow execution
	// and the event ID we are looking for is smaller than current next event ID
	if expectedNextEventID >= response.GetNextEventId() && response.GetWorkflowStatus() == enumspb.WORKFLOW_EXECUTION_STATUS_RUNNING {
		subscriberID, channel, err := e.eventNotifier.WatchHistoryEvent(definition.NewWorkflowIdentifier(namespaceID, execution.GetWorkflowId(), execution.GetRunId()))
		if err != nil {
			return nil, err
		}
		defer e.eventNotifier.UnwatchHistoryEvent(definition.NewWorkflowIdentifier(namespaceID, execution.GetWorkflowId(), execution.GetRunId()), subscriberID) // nolint:errcheck
		// check again in case the next event ID is updated
		response, err = e.getMutableState(ctx, namespaceID, execution)
		if err != nil {
			return nil, err
		}
		// check again if the current branch token changed
		if !bytes.Equal(request.CurrentBranchToken, response.CurrentBranchToken) {
			return nil, serviceerrors.NewCurrentBranchChanged(response.CurrentBranchToken, request.CurrentBranchToken)
		}
		if expectedNextEventID < response.GetNextEventId() || response.GetWorkflowStatus() != enumspb.WORKFLOW_EXECUTION_STATUS_RUNNING {
			return response, nil
		}

		namespaceCache, err := e.shard.GetNamespaceCache().GetNamespaceByID(namespaceID)
		if err != nil {
			return nil, err
		}
		timer := time.NewTimer(e.shard.GetConfig().LongPollExpirationInterval(namespaceCache.GetInfo().Name))
		defer timer.Stop()
		for {
			select {
			case event := <-channel:
				response.LastFirstEventId = event.LastFirstEventID
				response.LastFirstEventTxnId = event.LastFirstEventTxnID
				response.NextEventId = event.NextEventID
				response.PreviousStartedEventId = event.PreviousStartedEventID
				response.WorkflowState = event.WorkflowState
				response.WorkflowStatus = event.WorkflowStatus
				if !bytes.Equal(request.CurrentBranchToken, event.CurrentBranchToken) {
					return nil, serviceerrors.NewCurrentBranchChanged(event.CurrentBranchToken, request.CurrentBranchToken)
				}
				if expectedNextEventID < response.GetNextEventId() || response.GetWorkflowStatus() != enumspb.WORKFLOW_EXECUTION_STATUS_RUNNING {
					return response, nil
				}
			case <-timer.C:
				return response, nil
			case <-ctx.Done():
				return nil, ctx.Err()
			}
		}
	}

	return response, nil
}

func (e *historyEngineImpl) QueryWorkflow(
	ctx context.Context,
	request *historyservice.QueryWorkflowRequest,
) (_ *historyservice.QueryWorkflowResponse, retErr error) {

	scope := e.metricsClient.Scope(metrics.HistoryQueryWorkflowScope)

	mutableStateResp, err := e.getMutableState(ctx, request.GetNamespaceId(), *request.GetRequest().GetExecution())
	if err != nil {
		return nil, err
	}
	req := request.GetRequest()
	if mutableStateResp.GetWorkflowStatus() != enumspb.WORKFLOW_EXECUTION_STATUS_RUNNING && req.QueryRejectCondition != enumspb.QUERY_REJECT_CONDITION_NONE {
		notOpenReject := req.GetQueryRejectCondition() == enumspb.QUERY_REJECT_CONDITION_NOT_OPEN
		status := mutableStateResp.GetWorkflowStatus()
		notCompletedCleanlyReject := req.GetQueryRejectCondition() == enumspb.QUERY_REJECT_CONDITION_NOT_COMPLETED_CLEANLY && status != enumspb.WORKFLOW_EXECUTION_STATUS_COMPLETED
		if notOpenReject || notCompletedCleanlyReject {
			return &historyservice.QueryWorkflowResponse{
				Response: &workflowservice.QueryWorkflowResponse{
					QueryRejected: &querypb.QueryRejected{
						Status: status,
					},
				},
			}, nil
		}
	}

	de, err := e.shard.GetNamespaceCache().GetNamespaceByID(request.GetNamespaceId())
	if err != nil {
		return nil, err
	}

	context, release, err := e.historyCache.GetOrCreateWorkflowExecution(
		ctx,
		request.GetNamespaceId(),
		*request.GetRequest().GetExecution(),
		workflow.CallerTypeAPI,
	)
	if err != nil {
		return nil, err
	}
	defer func() { release(retErr) }()
	mutableState, err := context.LoadWorkflowExecution()
	if err != nil {
		return nil, err
	}

	// There are two ways in which queries get dispatched to workflow worker. First, queries can be dispatched on workflow tasks.
	// These workflow tasks potentially contain new events and queries. The events are treated as coming before the query in time.
	// The second way in which queries are dispatched to workflow worker is directly through matching; in this approach queries can be
	// dispatched to workflow worker immediately even if there are outstanding events that came before the query. The following logic
	// is used to determine if a query can be safely dispatched directly through matching or must be dispatched on a workflow task.
	//
	// There are three cases in which a query can be dispatched directly through matching safely, without violating strong consistency level:
	// 1. the namespace is not active, in this case history is immutable so a query dispatched at any time is consistent
	// 2. the workflow is not running, whenever a workflow is not running dispatching query directly is consistent
	// 3. if there is no pending or started workflow tasks it means no events came before query arrived, so its safe to dispatch directly
	safeToDispatchDirectly := !de.IsNamespaceActive() ||
		!mutableState.IsWorkflowExecutionRunning() ||
		(!mutableState.HasPendingWorkflowTask() && !mutableState.HasInFlightWorkflowTask())
	if safeToDispatchDirectly {
		release(nil)
		msResp, err := e.getMutableState(ctx, request.GetNamespaceId(), *request.GetRequest().GetExecution())
		if err != nil {
			return nil, err
		}
		req.Execution.RunId = msResp.Execution.RunId
		return e.queryDirectlyThroughMatching(ctx, msResp, request.GetNamespaceId(), req, scope)
	}

	// If we get here it means query could not be dispatched through matching directly, so it must block
	// until either an result has been obtained on a workflow task response or until it is safe to dispatch directly through matching.
	sw := scope.StartTimer(metrics.WorkflowTaskQueryLatency)
	defer sw.Stop()
	queryReg := mutableState.GetQueryRegistry()
	if len(queryReg.GetBufferedIDs()) >= e.config.MaxBufferedQueryCount() {
		scope.IncCounter(metrics.QueryBufferExceededCount)
		return nil, consts.ErrConsistentQueryBufferExceeded
	}
	queryID, termCh := queryReg.BufferQuery(req.GetQuery())
	defer queryReg.RemoveQuery(queryID)
	release(nil)
	select {
	case <-termCh:
		state, err := queryReg.GetTerminationState(queryID)
		if err != nil {
			scope.IncCounter(metrics.QueryRegistryInvalidStateCount)
			return nil, err
		}
		switch state.QueryTerminationType {
		case workflow.QueryTerminationTypeCompleted:
			result := state.QueryResult
			switch result.GetResultType() {
			case enumspb.QUERY_RESULT_TYPE_ANSWERED:
				return &historyservice.QueryWorkflowResponse{
					Response: &workflowservice.QueryWorkflowResponse{
						QueryResult: result.GetAnswer(),
					},
				}, nil
			case enumspb.QUERY_RESULT_TYPE_FAILED:
				return nil, serviceerror.NewQueryFailed(result.GetErrorMessage())
			default:
				scope.IncCounter(metrics.QueryRegistryInvalidStateCount)
				return nil, consts.ErrQueryEnteredInvalidState
			}
		case workflow.QueryTerminationTypeUnblocked:
			msResp, err := e.getMutableState(ctx, request.GetNamespaceId(), *request.GetRequest().GetExecution())
			if err != nil {
				return nil, err
			}
			req.Execution.RunId = msResp.Execution.RunId
			return e.queryDirectlyThroughMatching(ctx, msResp, request.GetNamespaceId(), req, scope)
		case workflow.QueryTerminationTypeFailed:
			return nil, state.Failure
		default:
			scope.IncCounter(metrics.QueryRegistryInvalidStateCount)
			return nil, consts.ErrQueryEnteredInvalidState
		}
	case <-ctx.Done():
		scope.IncCounter(metrics.ConsistentQueryTimeoutCount)
		return nil, ctx.Err()
	}
}

func (e *historyEngineImpl) queryDirectlyThroughMatching(
	ctx context.Context,
	msResp *historyservice.GetMutableStateResponse,
	namespaceID string,
	queryRequest *workflowservice.QueryWorkflowRequest,
	scope metrics.Scope,
) (*historyservice.QueryWorkflowResponse, error) {

	sw := scope.StartTimer(metrics.DirectQueryDispatchLatency)
	defer sw.Stop()

	if msResp.GetIsStickyTaskQueueEnabled() &&
		len(msResp.GetStickyTaskQueue().GetName()) != 0 &&
		e.config.EnableStickyQuery(queryRequest.GetNamespace()) {

		stickyMatchingRequest := &matchingservice.QueryWorkflowRequest{
			NamespaceId:  namespaceID,
			QueryRequest: queryRequest,
			TaskQueue:    msResp.GetStickyTaskQueue(),
		}

		// using a clean new context in case customer provide a context which has
		// a really short deadline, causing we clear the stickiness
		stickyContext, cancel := context.WithTimeout(context.Background(), timestamp.DurationValue(msResp.GetStickyTaskQueueScheduleToStartTimeout()))
		stickyStopWatch := scope.StartTimer(metrics.DirectQueryDispatchStickyLatency)
		matchingResp, err := e.rawMatchingClient.QueryWorkflow(stickyContext, stickyMatchingRequest)
		stickyStopWatch.Stop()
		cancel()
		if err == nil {
			scope.IncCounter(metrics.DirectQueryDispatchStickySuccessCount)
			return &historyservice.QueryWorkflowResponse{
				Response: &workflowservice.QueryWorkflowResponse{
					QueryResult:   matchingResp.GetQueryResult(),
					QueryRejected: matchingResp.GetQueryRejected(),
				}}, nil
		}
		if !common.IsContextDeadlineExceededErr(err) && !common.IsContextCanceledErr(err) {
			e.logger.Error("query directly though matching on sticky failed, will not attempt query on non-sticky",
				tag.WorkflowNamespace(queryRequest.GetNamespace()),
				tag.WorkflowID(queryRequest.Execution.GetWorkflowId()),
				tag.WorkflowRunID(queryRequest.Execution.GetRunId()),
				tag.WorkflowQueryType(queryRequest.Query.GetQueryType()),
				tag.Error(err))
			return nil, err
		}
		if msResp.GetWorkflowStatus() == enumspb.WORKFLOW_EXECUTION_STATUS_RUNNING {
			e.logger.Info("query direct through matching failed on sticky, clearing sticky before attempting on non-sticky",
				tag.WorkflowNamespace(queryRequest.GetNamespace()),
				tag.WorkflowID(queryRequest.Execution.GetWorkflowId()),
				tag.WorkflowRunID(queryRequest.Execution.GetRunId()),
				tag.WorkflowQueryType(queryRequest.Query.GetQueryType()))
			resetContext, cancel := context.WithTimeout(context.Background(), 5*time.Second)
			clearStickinessStopWatch := scope.StartTimer(metrics.DirectQueryDispatchClearStickinessLatency)
			_, err := e.ResetStickyTaskQueue(resetContext, &historyservice.ResetStickyTaskQueueRequest{
				NamespaceId: namespaceID,
				Execution:   queryRequest.GetExecution(),
			})
			clearStickinessStopWatch.Stop()
			cancel()
			if err != nil && err != consts.ErrWorkflowCompleted {
				return nil, err
			}
			scope.IncCounter(metrics.DirectQueryDispatchClearStickinessSuccessCount)
		}
	}

	if err := common.IsValidContext(ctx); err != nil {
		e.logger.Info("query context timed out before query on non-sticky task queue could be attempted",
			tag.WorkflowNamespace(queryRequest.GetNamespace()),
			tag.WorkflowID(queryRequest.Execution.GetWorkflowId()),
			tag.WorkflowRunID(queryRequest.Execution.GetRunId()),
			tag.WorkflowQueryType(queryRequest.Query.GetQueryType()))
		scope.IncCounter(metrics.DirectQueryDispatchTimeoutBeforeNonStickyCount)
		return nil, err
	}

	e.logger.Info("query directly through matching on sticky timed out, attempting to query on non-sticky",
		tag.WorkflowNamespace(queryRequest.GetNamespace()),
		tag.WorkflowID(queryRequest.Execution.GetWorkflowId()),
		tag.WorkflowRunID(queryRequest.Execution.GetRunId()),
		tag.WorkflowQueryType(queryRequest.Query.GetQueryType()),
		tag.WorkflowTaskQueueName(msResp.GetStickyTaskQueue().GetName()),
		tag.WorkflowNextEventID(msResp.GetNextEventId()))

	nonStickyMatchingRequest := &matchingservice.QueryWorkflowRequest{
		NamespaceId:  namespaceID,
		QueryRequest: queryRequest,
		TaskQueue:    msResp.TaskQueue,
	}

	nonStickyStopWatch := scope.StartTimer(metrics.DirectQueryDispatchNonStickyLatency)
	matchingResp, err := e.matchingClient.QueryWorkflow(ctx, nonStickyMatchingRequest)
	nonStickyStopWatch.Stop()
	if err != nil {
		e.logger.Error("query directly though matching on non-sticky failed",
			tag.WorkflowNamespace(queryRequest.GetNamespace()),
			tag.WorkflowID(queryRequest.Execution.GetWorkflowId()),
			tag.WorkflowRunID(queryRequest.Execution.GetRunId()),
			tag.WorkflowQueryType(queryRequest.Query.GetQueryType()),
			tag.Error(err))
		return nil, err
	}
	scope.IncCounter(metrics.DirectQueryDispatchNonStickySuccessCount)
	return &historyservice.QueryWorkflowResponse{
		Response: &workflowservice.QueryWorkflowResponse{
			QueryResult:   matchingResp.GetQueryResult(),
			QueryRejected: matchingResp.GetQueryRejected(),
		}}, err
}

func (e *historyEngineImpl) getMutableState(
	ctx context.Context,
	namespaceID string,
	execution commonpb.WorkflowExecution,
) (_ *historyservice.GetMutableStateResponse, retError error) {

	context, release, err := e.historyCache.GetOrCreateWorkflowExecution(
		ctx,
		namespaceID,
		execution,
		workflow.CallerTypeAPI,
	)
	if err != nil {
		return nil, err
	}
	defer func() { release(retError) }()

	mutableState, err := context.LoadWorkflowExecution()
	if err != nil {
		return nil, err
	}

	currentBranchToken, err := mutableState.GetCurrentBranchToken()
	if err != nil {
		return nil, err
	}

	executionInfo := mutableState.GetExecutionInfo()
	execution.RunId = context.GetExecution().RunId
	workflowState, workflowStatus := mutableState.GetWorkflowStateStatus()
	lastFirstEventID, lastFirstEventTxnID := mutableState.GetLastFirstEventIDTxnID()
	return &historyservice.GetMutableStateResponse{
		Execution:              &execution,
		WorkflowType:           &commonpb.WorkflowType{Name: executionInfo.WorkflowTypeName},
		LastFirstEventId:       lastFirstEventID,
		LastFirstEventTxnId:    lastFirstEventTxnID,
		NextEventId:            mutableState.GetNextEventID(),
		PreviousStartedEventId: mutableState.GetPreviousStartedEventID(),
		TaskQueue: &taskqueuepb.TaskQueue{
			Name: executionInfo.TaskQueue,
			Kind: enumspb.TASK_QUEUE_KIND_NORMAL,
		},
		StickyTaskQueue: &taskqueuepb.TaskQueue{
			Name: executionInfo.StickyTaskQueue,
			Kind: enumspb.TASK_QUEUE_KIND_STICKY,
		},
		StickyTaskQueueScheduleToStartTimeout: executionInfo.StickyScheduleToStartTimeout,
		CurrentBranchToken:                    currentBranchToken,
		WorkflowState:                         workflowState,
		WorkflowStatus:                        workflowStatus,
		IsStickyTaskQueueEnabled:              mutableState.IsStickyTaskQueueEnabled(),
		VersionHistories: versionhistory.CopyVersionHistories(
			mutableState.GetExecutionInfo().GetVersionHistories(),
		),
	}, nil
}

func (e *historyEngineImpl) DescribeMutableState(
	ctx context.Context,
	request *historyservice.DescribeMutableStateRequest,
) (response *historyservice.DescribeMutableStateResponse, retError error) {

	namespaceID, err := validateNamespaceUUID(request.GetNamespaceId())
	if err != nil {
		return nil, err
	}

	execution := commonpb.WorkflowExecution{
		WorkflowId: request.Execution.WorkflowId,
		RunId:      request.Execution.RunId,
	}

	context, release, err := e.historyCache.GetOrCreateWorkflowExecution(
		ctx,
		namespaceID,
		execution,
		workflow.CallerTypeAPI,
	)
	if err != nil {
		return nil, err
	}
	defer func() { release(retError) }()

	response = &historyservice.DescribeMutableStateResponse{}

	if context.(*workflow.ContextImpl).MutableState != nil {
		msb := context.(*workflow.ContextImpl).MutableState
		response.CacheMutableState = msb.CloneToProto()
	}

	context.Clear()
	mutableState, err := context.LoadWorkflowExecution()
	if err != nil {
		return nil, err
	}

	response.DatabaseMutableState = mutableState.CloneToProto()
	return response, nil
}

// ResetStickyTaskQueue reset the volatile information in mutable state of a given workflow.
// Volatile information are the information related to client, such as:
// 1. StickyTaskQueue
// 2. StickyScheduleToStartTimeout
func (e *historyEngineImpl) ResetStickyTaskQueue(
	ctx context.Context,
	resetRequest *historyservice.ResetStickyTaskQueueRequest,
) (*historyservice.ResetStickyTaskQueueResponse, error) {

	namespaceID, err := validateNamespaceUUID(resetRequest.GetNamespaceId())
	if err != nil {
		return nil, err
	}

	err = e.updateWorkflowExecution(
		ctx,
		namespaceID,
		*resetRequest.Execution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}

			mutableState.ClearStickyness()
			return &updateWorkflowAction{
				noop:               true,
				createWorkflowTask: false,
			}, nil
		},
	)

	if err != nil {
		return nil, err
	}
	return &historyservice.ResetStickyTaskQueueResponse{}, nil
}

// DescribeWorkflowExecution returns information about the specified workflow execution.
func (e *historyEngineImpl) DescribeWorkflowExecution(
	ctx context.Context,
	request *historyservice.DescribeWorkflowExecutionRequest,
) (_ *historyservice.DescribeWorkflowExecutionResponse, retError error) {

	namespaceID, err := validateNamespaceUUID(request.GetNamespaceId())
	if err != nil {
		return nil, err
	}

	execution := *request.Request.Execution

	context, release, err := e.historyCache.GetOrCreateWorkflowExecution(
		ctx,
		namespaceID,
		execution,
		workflow.CallerTypeAPI,
	)
	if err != nil {
		return nil, err
	}
	defer func() { release(retError) }()

	mutableState, err1 := context.LoadWorkflowExecution()
	if err1 != nil {
		return nil, err1
	}
	executionInfo := mutableState.GetExecutionInfo()
	executionState := mutableState.GetExecutionState()
	result := &historyservice.DescribeWorkflowExecutionResponse{
		ExecutionConfig: &workflowpb.WorkflowExecutionConfig{
			TaskQueue: &taskqueuepb.TaskQueue{
				Name: executionInfo.TaskQueue,
				Kind: enumspb.TASK_QUEUE_KIND_NORMAL,
			},
			WorkflowExecutionTimeout:   executionInfo.WorkflowExecutionTimeout,
			WorkflowRunTimeout:         executionInfo.WorkflowRunTimeout,
			DefaultWorkflowTaskTimeout: executionInfo.DefaultWorkflowTaskTimeout,
		},
		WorkflowExecutionInfo: &workflowpb.WorkflowExecutionInfo{
			Execution: &commonpb.WorkflowExecution{
				WorkflowId: executionInfo.WorkflowId,
				RunId:      executionState.RunId,
			},
			Type:                 &commonpb.WorkflowType{Name: executionInfo.WorkflowTypeName},
			StartTime:            executionInfo.StartTime,
			ExecutionTime:        executionInfo.ExecutionTime,
			HistoryLength:        mutableState.GetNextEventID() - common.FirstEventID,
			AutoResetPoints:      executionInfo.AutoResetPoints,
			Memo:                 &commonpb.Memo{Fields: executionInfo.Memo},
			SearchAttributes:     &commonpb.SearchAttributes{IndexedFields: executionInfo.SearchAttributes},
			Status:               executionState.Status,
			StateTransitionCount: executionInfo.StateTransitionCount,
		},
	}

	if executionInfo.ParentRunId != "" {
		result.WorkflowExecutionInfo.ParentExecution = &commonpb.WorkflowExecution{
			WorkflowId: executionInfo.ParentWorkflowId,
			RunId:      executionInfo.ParentRunId,
		}
		result.WorkflowExecutionInfo.ParentNamespaceId = executionInfo.ParentNamespaceId
	}
	if executionState.State == enumsspb.WORKFLOW_EXECUTION_STATE_COMPLETED {
		// for closed workflow
		result.WorkflowExecutionInfo.Status = executionState.Status
		completionEvent, err := mutableState.GetCompletionEvent()
		if err != nil {
			return nil, err
		}
		result.WorkflowExecutionInfo.CloseTime = completionEvent.GetEventTime()
	}

	if len(mutableState.GetPendingActivityInfos()) > 0 {
		for _, ai := range mutableState.GetPendingActivityInfos() {
			p := &workflowpb.PendingActivityInfo{
				ActivityId: ai.ActivityId,
			}
			if ai.CancelRequested {
				p.State = enumspb.PENDING_ACTIVITY_STATE_CANCEL_REQUESTED
			} else if ai.StartedId != common.EmptyEventID {
				p.State = enumspb.PENDING_ACTIVITY_STATE_STARTED
			} else {
				p.State = enumspb.PENDING_ACTIVITY_STATE_SCHEDULED
			}
			if !timestamp.TimeValue(ai.LastHeartbeatUpdateTime).IsZero() {
				p.LastHeartbeatTime = ai.LastHeartbeatUpdateTime
				p.HeartbeatDetails = ai.LastHeartbeatDetails
			}
			// TODO: move to mutable state instead of loading it from event
			scheduledEvent, err := mutableState.GetActivityScheduledEvent(ai.ScheduleId)
			if err != nil {
				return nil, err
			}
			p.ActivityType = scheduledEvent.GetActivityTaskScheduledEventAttributes().ActivityType
			if p.State == enumspb.PENDING_ACTIVITY_STATE_SCHEDULED {
				p.ScheduledTime = ai.ScheduledTime
			} else {
				p.LastStartedTime = ai.StartedTime
			}
			if ai.HasRetryPolicy {
				p.Attempt = ai.Attempt
				p.ExpirationTime = ai.RetryExpirationTime
				if ai.RetryMaximumAttempts != 0 {
					p.MaximumAttempts = ai.RetryMaximumAttempts
				}
				if ai.RetryLastFailure != nil {
					p.LastFailure = ai.RetryLastFailure
				}
				if ai.RetryLastWorkerIdentity != "" {
					p.LastWorkerIdentity = ai.RetryLastWorkerIdentity
				}
			} else {
				p.Attempt = 1
			}
			result.PendingActivities = append(result.PendingActivities, p)
		}
	}

	if len(mutableState.GetPendingChildExecutionInfos()) > 0 {
		for _, ch := range mutableState.GetPendingChildExecutionInfos() {
			p := &workflowpb.PendingChildExecutionInfo{
				WorkflowId:        ch.StartedWorkflowId,
				RunId:             ch.StartedRunId,
				WorkflowTypeName:  ch.WorkflowTypeName,
				InitiatedId:       ch.InitiatedId,
				ParentClosePolicy: ch.ParentClosePolicy,
			}
			result.PendingChildren = append(result.PendingChildren, p)
		}
	}

	return result, nil
}

func (e *historyEngineImpl) RecordActivityTaskStarted(
	ctx context.Context,
	request *historyservice.RecordActivityTaskStartedRequest,
) (*historyservice.RecordActivityTaskStartedResponse, error) {

	namespaceEntry, err := e.getActiveNamespaceEntry(request.GetNamespaceId())
	if err != nil {
		return nil, err
	}

	namespaceInfo := namespaceEntry.GetInfo()

	namespaceID := namespaceInfo.Id
	namespace := namespaceInfo.Name

	execution := commonpb.WorkflowExecution{
		WorkflowId: request.WorkflowExecution.WorkflowId,
		RunId:      request.WorkflowExecution.RunId,
	}

	response := &historyservice.RecordActivityTaskStartedResponse{}
	err = e.updateWorkflowExecution(
		ctx,
		namespaceID,
		execution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}

			scheduleID := request.GetScheduleId()
			requestID := request.GetRequestId()
			ai, isRunning := mutableState.GetActivityInfo(scheduleID)

			metricsScope := e.metricsClient.Scope(metrics.HistoryRecordActivityTaskStartedScope)

			// First check to see if cache needs to be refreshed as we could potentially have stale workflow execution in
			// some extreme cassandra failure cases.
			if !isRunning && scheduleID >= mutableState.GetNextEventID() {
				metricsScope.IncCounter(metrics.StaleMutableStateCounter)
				return nil, consts.ErrStaleState
			}

			// Check execution state to make sure task is in the list of outstanding tasks and it is not yet started.  If
			// task is not outstanding than it is most probably a duplicate and complete the task.
			if !isRunning {
				// Looks like ActivityTask already completed as a result of another call.
				// It is OK to drop the task at this point.
				e.logger.Debug("Potentially duplicate task.", tag.TaskID(request.GetTaskId()), tag.WorkflowScheduleID(scheduleID), tag.TaskType(enumsspb.TASK_TYPE_TRANSFER_ACTIVITY_TASK))
				return nil, consts.ErrActivityTaskNotFound
			}

			scheduledEvent, err := mutableState.GetActivityScheduledEvent(scheduleID)
			if err != nil {
				return nil, err
			}
			response.ScheduledEvent = scheduledEvent
			response.CurrentAttemptScheduledTime = ai.ScheduledTime

			if ai.StartedId != common.EmptyEventID {
				// If activity is started as part of the current request scope then return a positive response
				if ai.RequestId == requestID {
					response.StartedTime = ai.StartedTime
					response.Attempt = ai.Attempt
					return &updateWorkflowAction{
						noop:               false,
						createWorkflowTask: false,
					}, nil
				}

				// Looks like ActivityTask already started as a result of another call.
				// It is OK to drop the task at this point.
				e.logger.Debug("Potentially duplicate task.", tag.TaskID(request.GetTaskId()), tag.WorkflowScheduleID(scheduleID), tag.TaskType(enumsspb.TASK_TYPE_TRANSFER_ACTIVITY_TASK))
				return nil, serviceerrors.NewTaskAlreadyStarted("Activity")
			}

			if _, err := mutableState.AddActivityTaskStartedEvent(
				ai, scheduleID, requestID, request.PollRequest.GetIdentity(),
			); err != nil {
				return nil, err
			}

			scheduleToStartLatency := ai.GetStartedTime().Sub(*ai.GetScheduledTime())
			namespaceName := namespaceEntry.GetInfo().GetName()
			taskQueueName := ai.GetTaskQueue()

			metrics.GetPerTaskQueueScope(metricsScope, namespaceName, taskQueueName, enumspb.TASK_QUEUE_KIND_NORMAL).
				Tagged(metrics.TaskTypeTag("activity")).
				RecordTimer(metrics.TaskScheduleToStartLatency, scheduleToStartLatency)

			response.StartedTime = ai.StartedTime
			response.Attempt = ai.Attempt
			response.HeartbeatDetails = ai.LastHeartbeatDetails

			response.WorkflowType = mutableState.GetWorkflowType()
			response.WorkflowNamespace = namespace

			return &updateWorkflowAction{
				noop:               false,
				createWorkflowTask: false,
			}, nil
		})

	if err != nil {
		return nil, err
	}

	return response, err
}

// ScheduleWorkflowTask schedules a workflow task if no outstanding workflow task found
func (e *historyEngineImpl) ScheduleWorkflowTask(
	ctx context.Context,
	req *historyservice.ScheduleWorkflowTaskRequest,
) error {
	return e.workflowTaskHandler.handleWorkflowTaskScheduled(ctx, req)
}

// RecordWorkflowTaskStarted starts a workflow task
func (e *historyEngineImpl) RecordWorkflowTaskStarted(
	ctx context.Context,
	request *historyservice.RecordWorkflowTaskStartedRequest,
) (*historyservice.RecordWorkflowTaskStartedResponse, error) {
	return e.workflowTaskHandler.handleWorkflowTaskStarted(ctx, request)
}

// RespondWorkflowTaskCompleted completes a workflow task
func (e *historyEngineImpl) RespondWorkflowTaskCompleted(
	ctx context.Context,
	req *historyservice.RespondWorkflowTaskCompletedRequest,
) (*historyservice.RespondWorkflowTaskCompletedResponse, error) {
	return e.workflowTaskHandler.handleWorkflowTaskCompleted(ctx, req)
}

// RespondWorkflowTaskFailed fails a workflow task
func (e *historyEngineImpl) RespondWorkflowTaskFailed(
	ctx context.Context,
	req *historyservice.RespondWorkflowTaskFailedRequest,
) error {
	return e.workflowTaskHandler.handleWorkflowTaskFailed(ctx, req)
}

// RespondActivityTaskCompleted completes an activity task.
func (e *historyEngineImpl) RespondActivityTaskCompleted(
	ctx context.Context,
	req *historyservice.RespondActivityTaskCompletedRequest,
) error {

	namespaceEntry, err := e.getActiveNamespaceEntry(req.GetNamespaceId())
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id
	namespace := namespaceEntry.GetInfo().Name

	request := req.CompleteRequest
	token, err0 := e.tokenSerializer.Deserialize(request.TaskToken)
	if err0 != nil {
		return consts.ErrDeserializingToken
	}

	workflowExecution := commonpb.WorkflowExecution{
		WorkflowId: token.GetWorkflowId(),
		RunId:      token.GetRunId(),
	}

	var activityStartedTime time.Time
	var taskQueue string
	var workflowTypeName string
	err = e.updateWorkflowExecution(
		ctx,
		namespaceID,
		workflowExecution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			workflowTypeName = mutableState.GetWorkflowType().GetName()
			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}
			scheduleID := token.GetScheduleId()
			if scheduleID == common.EmptyEventID { // client call CompleteActivityById, so get scheduleID by activityID
				scheduleID, err0 = getScheduleID(token.GetActivityId(), mutableState)
				if err0 != nil {
					return nil, err0
				}
			}
			ai, isRunning := mutableState.GetActivityInfo(scheduleID)

			// First check to see if cache needs to be refreshed as we could potentially have stale workflow execution in
			// some extreme cassandra failure cases.
			if !isRunning && scheduleID >= mutableState.GetNextEventID() {
				e.metricsClient.IncCounter(metrics.HistoryRespondActivityTaskCompletedScope, metrics.StaleMutableStateCounter)
				return nil, consts.ErrStaleState
			}

			if !isRunning || ai.StartedId == common.EmptyEventID ||
				(token.GetScheduleId() != common.EmptyEventID && token.ScheduleAttempt != ai.Attempt) {
				return nil, consts.ErrActivityTaskNotFound
			}

			if _, err := mutableState.AddActivityTaskCompletedEvent(scheduleID, ai.StartedId, request); err != nil {
				// Unable to add ActivityTaskCompleted event to history
				return nil, serviceerror.NewUnavailable("Unable to add ActivityTaskCompleted event to history.")
			}
			activityStartedTime = *ai.StartedTime
			taskQueue = ai.TaskQueue
			return &updateWorkflowAction{
				noop:               false,
				createWorkflowTask: true,
			}, nil
		})

	if err == nil && !activityStartedTime.IsZero() {
		scope := e.metricsClient.Scope(metrics.HistoryRespondActivityTaskCompletedScope).
			Tagged(
				metrics.NamespaceTag(namespace),
				metrics.WorkflowTypeTag(workflowTypeName),
				metrics.ActivityTypeTag(token.ActivityType),
				metrics.TaskQueueTag(taskQueue),
			)
		scope.RecordTimer(metrics.ActivityE2ELatency, time.Since(activityStartedTime))
	}
	return err
}

// RespondActivityTaskFailed completes an activity task failure.
func (e *historyEngineImpl) RespondActivityTaskFailed(
	ctx context.Context,
	req *historyservice.RespondActivityTaskFailedRequest,
) error {

	namespaceEntry, err := e.getActiveNamespaceEntry(req.GetNamespaceId())
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id
	namespace := namespaceEntry.GetInfo().Name

	request := req.FailedRequest
	token, err0 := e.tokenSerializer.Deserialize(request.TaskToken)
	if err0 != nil {
		return consts.ErrDeserializingToken
	}

	workflowExecution := commonpb.WorkflowExecution{
		WorkflowId: token.GetWorkflowId(),
		RunId:      token.GetRunId(),
	}

	var activityStartedTime time.Time
	var taskQueue string
	var workflowTypeName string
	err = e.updateWorkflowExecution(ctx, namespaceID, workflowExecution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			workflowTypeName = mutableState.GetWorkflowType().GetName()
			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}

			scheduleID := token.GetScheduleId()
			if scheduleID == common.EmptyEventID { // client call CompleteActivityById, so get scheduleID by activityID
				scheduleID, err0 = getScheduleID(token.GetActivityId(), mutableState)
				if err0 != nil {
					return nil, err0
				}
			}
			ai, isRunning := mutableState.GetActivityInfo(scheduleID)

			// First check to see if cache needs to be refreshed as we could potentially have stale workflow execution in
			// some extreme cassandra failure cases.
			if !isRunning && scheduleID >= mutableState.GetNextEventID() {
				e.metricsClient.IncCounter(metrics.HistoryRespondActivityTaskFailedScope, metrics.StaleMutableStateCounter)
				return nil, consts.ErrStaleState
			}

			if !isRunning || ai.StartedId == common.EmptyEventID ||
				(token.GetScheduleId() != common.EmptyEventID && token.ScheduleAttempt != ai.Attempt) {
				return nil, consts.ErrActivityTaskNotFound
			}

			postActions := &updateWorkflowAction{}
			failure := request.GetFailure()
			retryState, err := mutableState.RetryActivity(ai, failure)
			if err != nil {
				return nil, err
			}
			if retryState != enumspb.RETRY_STATE_IN_PROGRESS {
				// no more retry, and we want to record the failure event
				if _, err := mutableState.AddActivityTaskFailedEvent(scheduleID, ai.StartedId, failure, retryState, request.GetIdentity()); err != nil {
					// Unable to add ActivityTaskFailed event to history
					return nil, serviceerror.NewUnavailable("Unable to add ActivityTaskFailed event to history.")
				}
				postActions.createWorkflowTask = true
			}

			activityStartedTime = *ai.StartedTime
			taskQueue = ai.TaskQueue
			return postActions, nil
		})
	if err == nil && !activityStartedTime.IsZero() {
		scope := e.metricsClient.Scope(metrics.HistoryRespondActivityTaskFailedScope).
			Tagged(
				metrics.NamespaceTag(namespace),
				metrics.WorkflowTypeTag(workflowTypeName),
				metrics.ActivityTypeTag(token.ActivityType),
				metrics.TaskQueueTag(taskQueue),
			)
		scope.RecordTimer(metrics.ActivityE2ELatency, time.Since(activityStartedTime))
	}
	return err
}

// RespondActivityTaskCanceled completes an activity task failure.
func (e *historyEngineImpl) RespondActivityTaskCanceled(
	ctx context.Context,
	req *historyservice.RespondActivityTaskCanceledRequest,
) error {

	namespaceEntry, err := e.getActiveNamespaceEntry(req.GetNamespaceId())
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id
	namespace := namespaceEntry.GetInfo().Name

	request := req.CancelRequest
	token, err0 := e.tokenSerializer.Deserialize(request.TaskToken)
	if err0 != nil {
		return consts.ErrDeserializingToken
	}

	workflowExecution := commonpb.WorkflowExecution{
		WorkflowId: token.GetWorkflowId(),
		RunId:      token.GetRunId(),
	}

	var activityStartedTime time.Time
	var taskQueue string
	var workflowTypeName string
	err = e.updateWorkflowExecution(
		ctx,
		namespaceID,
		workflowExecution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			workflowTypeName = mutableState.GetWorkflowType().GetName()
			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}

			scheduleID := token.GetScheduleId()
			if scheduleID == common.EmptyEventID { // client call CompleteActivityById, so get scheduleID by activityID
				scheduleID, err0 = getScheduleID(token.GetActivityId(), mutableState)
				if err0 != nil {
					return nil, err0
				}
			}
			ai, isRunning := mutableState.GetActivityInfo(scheduleID)

			// First check to see if cache needs to be refreshed as we could potentially have stale workflow execution in
			// some extreme cassandra failure cases.
			if !isRunning && scheduleID >= mutableState.GetNextEventID() {
				e.metricsClient.IncCounter(metrics.HistoryRespondActivityTaskCanceledScope, metrics.StaleMutableStateCounter)
				return nil, consts.ErrStaleState
			}

			if !isRunning || ai.StartedId == common.EmptyEventID ||
				(token.GetScheduleId() != common.EmptyEventID && token.ScheduleAttempt != ai.Attempt) {
				return nil, consts.ErrActivityTaskNotFound
			}

			if _, err := mutableState.AddActivityTaskCanceledEvent(
				scheduleID,
				ai.StartedId,
				ai.CancelRequestId,
				request.Details,
				request.Identity); err != nil {
				// Unable to add ActivityTaskCanceled event to history
				return nil, serviceerror.NewUnavailable("Unable to add ActivityTaskCanceled event to history.")
			}

			activityStartedTime = *ai.StartedTime
			taskQueue = ai.TaskQueue
			return &updateWorkflowAction{
				noop:               false,
				createWorkflowTask: true,
			}, nil
		})

	if err == nil && !activityStartedTime.IsZero() {
		scope := e.metricsClient.Scope(metrics.HistoryRespondActivityTaskCanceledScope).
			Tagged(
				metrics.NamespaceTag(namespace),
				metrics.WorkflowTypeTag(workflowTypeName),
				metrics.ActivityTypeTag(token.ActivityType),
				metrics.TaskQueueTag(taskQueue),
			)
		scope.RecordTimer(metrics.ActivityE2ELatency, time.Since(activityStartedTime))
	}
	return err
}

// RecordActivityTaskHeartbeat records an hearbeat for a task.
// This method can be used for two purposes.
// - For reporting liveness of the activity.
// - For reporting progress of the activity, this can be done even if the liveness is not configured.
func (e *historyEngineImpl) RecordActivityTaskHeartbeat(
	ctx context.Context,
	req *historyservice.RecordActivityTaskHeartbeatRequest,
) (*historyservice.RecordActivityTaskHeartbeatResponse, error) {

	namespaceEntry, err := e.getActiveNamespaceEntry(req.GetNamespaceId())
	if err != nil {
		return nil, err
	}
	namespaceID := namespaceEntry.GetInfo().Id

	request := req.HeartbeatRequest
	token, err0 := e.tokenSerializer.Deserialize(request.TaskToken)
	if err0 != nil {
		return nil, consts.ErrDeserializingToken
	}

	workflowExecution := commonpb.WorkflowExecution{
		WorkflowId: token.GetWorkflowId(),
		RunId:      token.GetRunId(),
	}

	var cancelRequested bool
	err = e.updateWorkflowExecution(
		ctx,
		namespaceID,
		workflowExecution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			if !mutableState.IsWorkflowExecutionRunning() {
				e.logger.Debug("Heartbeat failed")
				return nil, consts.ErrWorkflowCompleted
			}

			scheduleID := token.GetScheduleId()
			if scheduleID == common.EmptyEventID { // client call RecordActivityHeartbeatByID, so get scheduleID by activityID
				scheduleID, err0 = getScheduleID(token.GetActivityId(), mutableState)
				if err0 != nil {
					return nil, err0
				}
			}
			ai, isRunning := mutableState.GetActivityInfo(scheduleID)

			// First check to see if cache needs to be refreshed as we could potentially have stale workflow execution in
			// some extreme cassandra failure cases.
			if !isRunning && scheduleID >= mutableState.GetNextEventID() {
				e.metricsClient.IncCounter(metrics.HistoryRecordActivityTaskHeartbeatScope, metrics.StaleMutableStateCounter)
				return nil, consts.ErrStaleState
			}

			if !isRunning || ai.StartedId == common.EmptyEventID ||
				(token.GetScheduleId() != common.EmptyEventID && token.ScheduleAttempt != ai.Attempt) {
				return nil, consts.ErrActivityTaskNotFound
			}

			cancelRequested = ai.CancelRequested

			e.logger.Debug("Activity heartbeat", tag.WorkflowScheduleID(scheduleID), tag.ActivityInfo(ai), tag.Bool(cancelRequested))

			// Save progress and last HB reported time.
			mutableState.UpdateActivityProgress(ai, request)

			return &updateWorkflowAction{
				noop:               false,
				createWorkflowTask: false,
			}, nil
		})

	if err != nil {
		return &historyservice.RecordActivityTaskHeartbeatResponse{}, err
	}

	return &historyservice.RecordActivityTaskHeartbeatResponse{CancelRequested: cancelRequested}, nil
}

// RequestCancelWorkflowExecution records request cancellation event for workflow execution
func (e *historyEngineImpl) RequestCancelWorkflowExecution(
	ctx context.Context,
	req *historyservice.RequestCancelWorkflowExecutionRequest,
) error {

	namespaceEntry, err := e.getActiveNamespaceEntry(req.GetNamespaceId())
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id

	request := req.CancelRequest
	parentExecution := req.ExternalWorkflowExecution
	childWorkflowOnly := req.GetChildWorkflowOnly()
	execution := commonpb.WorkflowExecution{
		WorkflowId: request.WorkflowExecution.WorkflowId,
	}

	firstExecutionRunID := request.GetFirstExecutionRunId()
	// If firstExecutionRunID is set on the request always try to cancel currently running execution
	if len(firstExecutionRunID) == 0 {
		execution.RunId = request.WorkflowExecution.RunId
	}

	return e.updateWorkflow(ctx, namespaceID, execution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			if !mutableState.IsWorkflowExecutionRunning() {
				// the request to cancel this workflow is a success even
				// if the target workflow has already finished
				return &updateWorkflowAction{
					noop:               true,
					createWorkflowTask: false,
				}, nil
			}

			// There is a workflow execution currently running with the WorkflowID.
			// If user passed in a FirstExecutionRunID with the request to allow cancel to work across runs then
			// let's compare the FirstExecutionRunID on the request to make sure we cancel the correct workflow
			// execution.
			executionInfo := mutableState.GetExecutionInfo()
			if len(firstExecutionRunID) > 0 && executionInfo.FirstExecutionRunId != firstExecutionRunID {
				return nil, consts.ErrWorkflowExecutionNotFound
			}

			if childWorkflowOnly {
				parentWorkflowID := executionInfo.ParentWorkflowId
				parentRunID := executionInfo.ParentRunId
				if parentExecution.GetWorkflowId() != parentWorkflowID ||
					parentExecution.GetRunId() != parentRunID {
					return nil, consts.ErrWorkflowParent
				}
			}

			isCancelRequested := mutableState.IsCancelRequested()
			if isCancelRequested {
				// since cancellation is idempotent
				return &updateWorkflowAction{
					noop:               true,
					createWorkflowTask: false,
				}, nil
			}

			if _, err := mutableState.AddWorkflowExecutionCancelRequestedEvent(req); err != nil {
				return nil, serviceerror.NewUnavailable("Unable to cancel workflow execution.")
			}

			return updateWorkflowWithNewWorkflowTask, nil
		})
}

func (e *historyEngineImpl) SignalWorkflowExecution(
	ctx context.Context,
	signalRequest *historyservice.SignalWorkflowExecutionRequest,
) error {

	namespaceEntry, err := e.getActiveNamespaceEntry(signalRequest.GetNamespaceId())
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id

	request := signalRequest.SignalRequest
	parentExecution := signalRequest.ExternalWorkflowExecution
	childWorkflowOnly := signalRequest.GetChildWorkflowOnly()
	execution := commonpb.WorkflowExecution{
		WorkflowId: request.WorkflowExecution.WorkflowId,
		RunId:      request.WorkflowExecution.RunId,
	}

	return e.updateWorkflow(
		ctx,
		namespaceID,
		execution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			if request.GetRequestId() != "" && mutableState.IsSignalRequested(request.GetRequestId()) {
				return &updateWorkflowAction{
					noop:               true,
					createWorkflowTask: false,
				}, nil
			}

			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}

			executionInfo := mutableState.GetExecutionInfo()
			createWorkflowTask := true
			// Do not create workflow task when the workflow is cron and the cron has not been started yet
			if executionInfo.CronSchedule != "" && !mutableState.HasProcessedOrPendingWorkflowTask() {
				createWorkflowTask = false
			}

			maxAllowedSignals := e.config.MaximumSignalsPerExecution(namespaceEntry.GetInfo().Name)
			if maxAllowedSignals > 0 && int(executionInfo.SignalCount) >= maxAllowedSignals {
				e.logger.Info("Execution limit reached for maximum signals", tag.WorkflowSignalCount(executionInfo.SignalCount),
					tag.WorkflowID(execution.GetWorkflowId()),
					tag.WorkflowRunID(execution.GetRunId()),
					tag.WorkflowNamespaceID(namespaceID))
				return nil, consts.ErrSignalsLimitExceeded
			}

			if childWorkflowOnly {
				parentWorkflowID := executionInfo.ParentWorkflowId
				parentRunID := executionInfo.ParentRunId
				if parentExecution.GetWorkflowId() != parentWorkflowID ||
					parentExecution.GetRunId() != parentRunID {
					return nil, consts.ErrWorkflowParent
				}
			}

			if request.GetRequestId() != "" {
				mutableState.AddSignalRequested(request.GetRequestId())
			}
			if _, err := mutableState.AddWorkflowExecutionSignaled(
				request.GetSignalName(),
				request.GetInput(),
				request.GetIdentity()); err != nil {
				return nil, serviceerror.NewUnavailable("Unable to signal workflow execution.")
			}

			return &updateWorkflowAction{
				noop:               false,
				createWorkflowTask: createWorkflowTask,
			}, nil
		})
}

func (e *historyEngineImpl) SignalWithStartWorkflowExecution(
	ctx context.Context,
	signalWithStartRequest *historyservice.SignalWithStartWorkflowExecutionRequest,
) (_ *historyservice.SignalWithStartWorkflowExecutionResponse, retError error) {

	namespaceEntry, err := e.getActiveNamespaceEntry(signalWithStartRequest.GetNamespaceId())
	if err != nil {
		return nil, err
	}
	namespaceID := namespaceEntry.GetInfo().Id
	namespace := namespaceEntry.GetInfo().Name

	sRequest := signalWithStartRequest.SignalWithStartRequest
	execution := commonpb.WorkflowExecution{
		WorkflowId: sRequest.WorkflowId,
	}

	var prevMutableState workflow.MutableState
	attempt := 1

	context, release, err0 := e.historyCache.GetOrCreateWorkflowExecution(
		ctx,
		namespaceID,
		execution,
		workflow.CallerTypeAPI,
	)

	if err0 == nil {
		defer func() { release(retError) }()
	Just_Signal_Loop:
		for ; attempt <= conditionalRetryCount; attempt++ {
			// workflow not exist, will create workflow then signal
			mutableState, err1 := context.LoadWorkflowExecution()
			if err1 != nil {
				if _, ok := err1.(*serviceerror.NotFound); ok {
					break
				}
				return nil, err1
			}
			// workflow exist but not running, will restart workflow then signal
			if !mutableState.IsWorkflowExecutionRunning() {
				prevMutableState = mutableState
				break
			}

			executionInfo := mutableState.GetExecutionInfo()
			maxAllowedSignals := e.config.MaximumSignalsPerExecution(namespace)
			if maxAllowedSignals > 0 && int(executionInfo.SignalCount) >= maxAllowedSignals {
				e.logger.Info("Execution limit reached for maximum signals", tag.WorkflowSignalCount(executionInfo.SignalCount),
					tag.WorkflowID(execution.GetWorkflowId()),
					tag.WorkflowRunID(execution.GetRunId()),
					tag.WorkflowNamespaceID(namespaceID))
				return nil, consts.ErrSignalsLimitExceeded
			}

			if _, err := mutableState.AddWorkflowExecutionSignaled(
				sRequest.GetSignalName(),
				sRequest.GetSignalInput(),
				sRequest.GetIdentity()); err != nil {
				return nil, serviceerror.NewUnavailable("Unable to signal workflow execution.")
			}

			// Create a transfer task to schedule a workflow task
			if !mutableState.HasPendingWorkflowTask() {
				_, err := mutableState.AddWorkflowTaskScheduledEvent(false)
				if err != nil {
					return nil, serviceerror.NewUnavailable("Failed to add workflow task scheduled event.")
				}
			}

			// We apply the update to execution using optimistic concurrency.  If it fails due to a conflict then reload
			// the history and try the operation again.
			if err := context.UpdateWorkflowExecutionAsActive(e.shard.GetTimeSource().Now()); err != nil {
				if err == consts.ErrConflict {
					continue Just_Signal_Loop
				}
				return nil, err
			}
			return &historyservice.SignalWithStartWorkflowExecutionResponse{RunId: context.GetExecution().RunId}, nil
		} // end for Just_Signal_Loop
		if attempt == conditionalRetryCount+1 {
			return nil, consts.ErrMaxAttemptsExceeded
		}
	} else {
		if _, ok := err0.(*serviceerror.NotFound); !ok {
			return nil, err0
		}
		// workflow not exist, will create workflow then signal
	}

	// Start workflow and signal
	startRequest := e.getStartRequest(namespaceID, sRequest)
	request := startRequest.StartRequest
	e.overrideStartWorkflowExecutionRequest(request, metrics.HistorySignalWithStartWorkflowExecutionScope)
	err = e.validateStartWorkflowExecutionRequest(ctx, request, namespace, "SignalWithStartWorkflowExecution")
	if err != nil {
		return nil, err
	}

	err = searchattribute.SubstituteAliases(e.searchAttributesMapper, request.GetSearchAttributes(), namespace)
	if err != nil {
		return nil, err
	}

	if err := common.CheckEventBlobSizeLimit(
		sRequest.GetSignalInput().Size(),
		e.config.BlobSizeLimitWarn(namespace),
		e.config.BlobSizeLimitError(namespace),
		namespaceID,
		sRequest.GetWorkflowId(),
		"",
		e.metricsScope(ctx).Tagged(metrics.CommandTypeTag(enumspb.COMMAND_TYPE_UNSPECIFIED.String())),
		e.throttledLogger,
		tag.BlobSizeViolationOperation("SignalWithStartWorkflowExecution"),
	); err != nil {
		return nil, err
	}

	workflowID := request.GetWorkflowId()
	// grab the current context as a Lock, nothing more
	_, currentRelease, err := e.historyCache.GetOrCreateCurrentWorkflowExecution(
		ctx,
		namespaceID,
		workflowID,
	)
	if err != nil {
		return nil, err
	}
	defer func() { currentRelease(retError) }()

	execution = commonpb.WorkflowExecution{
		WorkflowId: workflowID,
		RunId:      uuid.New(),
	}

	clusterMetadata := e.shard.GetService().GetClusterMetadata()
	mutableState, err := createMutableState(e.shard, namespaceEntry, execution.GetRunId())
	if err != nil {
		return nil, err
	}

	if prevMutableState != nil {
		prevLastWriteVersion, err := prevMutableState.GetLastWriteVersion()
		if err != nil {
			return nil, err
		}
		if prevLastWriteVersion > mutableState.GetCurrentVersion() {
			return nil, serviceerror.NewNamespaceNotActive(
				namespace,
				clusterMetadata.GetCurrentClusterName(),
				clusterMetadata.ClusterNameForFailoverVersion(prevLastWriteVersion),
			)
		}

		err = e.applyWorkflowIDReusePolicyForSigWithStart(prevMutableState.GetExecutionState(), namespaceID, execution, request.WorkflowIdReusePolicy)
		if err != nil {
			return nil, err
		}
	}

	// Add WF start event
	startEvent, err := mutableState.AddWorkflowExecutionStartedEvent(
		execution,
		startRequest,
	)
	if err != nil {
		return nil, serviceerror.NewUnavailable("Failed to add workflow execution started event.")
	}

	// Add signal event
	if _, err := mutableState.AddWorkflowExecutionSignaled(
		sRequest.GetSignalName(),
		sRequest.GetSignalInput(),
		sRequest.GetIdentity()); err != nil {
		return nil, serviceerror.NewUnavailable("Failed to add workflow execution signaled event.")
	}

	if err = e.generateFirstWorkflowTask(
		mutableState,
		startRequest.ParentExecutionInfo,
		startEvent,
	); err != nil {
		return nil, err
	}

	context = workflow.NewContext(namespaceID, execution, e.shard, e.logger)

	now := e.timeSource.Now()
	newWorkflow, newWorkflowEventsSeq, err := mutableState.CloseTransactionAsSnapshot(
		now,
		workflow.TransactionPolicyActive,
	)
	if err != nil {
		return nil, err
	}
	if len(newWorkflowEventsSeq) != 1 {
		return nil, serviceerror.NewUnavailable("unable to create 1st event batch")
	}

	createMode := persistence.CreateWorkflowModeBrandNew
	prevRunID := ""
	prevLastWriteVersion := int64(0)
	if prevMutableState != nil {
		createMode = persistence.CreateWorkflowModeWorkflowIDReuse
		prevRunID = prevMutableState.GetExecutionState().GetRunId()
		prevLastWriteVersion, err = prevMutableState.GetLastWriteVersion()
		if err != nil {
			return nil, err
		}
	}
	err = context.CreateWorkflowExecution(
		now,
		createMode,
		prevRunID,
		prevLastWriteVersion,
		mutableState,
		newWorkflow,
		newWorkflowEventsSeq,
	)

	if t, ok := err.(*persistence.CurrentWorkflowConditionFailedError); ok {
		if t.RequestID == request.GetRequestId() {
			return &historyservice.SignalWithStartWorkflowExecutionResponse{
				RunId: t.RunID,
			}, nil
			// delete history is expected here because duplicate start request will create history with different rid
		}
		return nil, err
	}

	if err != nil {
		return nil, err
	}
	return &historyservice.SignalWithStartWorkflowExecutionResponse{
		RunId: execution.RunId,
	}, nil
}

// RemoveSignalMutableState remove the signal request id in signal_requested for deduplicate
func (e *historyEngineImpl) RemoveSignalMutableState(
	ctx context.Context,
	request *historyservice.RemoveSignalMutableStateRequest,
) error {

	namespaceEntry, err := e.getActiveNamespaceEntry(request.GetNamespaceId())
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id

	execution := commonpb.WorkflowExecution{
		WorkflowId: request.WorkflowExecution.WorkflowId,
		RunId:      request.WorkflowExecution.RunId,
	}

	return e.updateWorkflowExecution(
		ctx,
		namespaceID,
		execution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}

			mutableState.DeleteSignalRequested(request.GetRequestId())
			return &updateWorkflowAction{
				noop:               false,
				createWorkflowTask: false,
			}, nil
		})
}

func (e *historyEngineImpl) TerminateWorkflowExecution(
	ctx context.Context,
	terminateRequest *historyservice.TerminateWorkflowExecutionRequest,
) error {

	namespaceEntry, err := e.getActiveNamespaceEntry(terminateRequest.GetNamespaceId())
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id

	request := terminateRequest.TerminateRequest
	execution := commonpb.WorkflowExecution{
		WorkflowId: request.WorkflowExecution.WorkflowId,
	}

	firstExecutionRunID := request.GetFirstExecutionRunId()
	// If firstExecutionRunID is set on the request always try to terminate currently running execution
	if len(firstExecutionRunID) == 0 {
		execution.RunId = request.WorkflowExecution.RunId
	}

	return e.updateWorkflow(
		ctx,
		namespaceID,
		execution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}

			// There is a workflow execution currently running with the WorkflowID.
			// If user passed in a FirstExecutionRunID with the request to allow terminate to work across runs then
			// let's compare the FirstExecutionRunID on the request to make sure we terminate the correct workflow
			// execution.
			executionInfo := mutableState.GetExecutionInfo()
			if len(firstExecutionRunID) > 0 && executionInfo.FirstExecutionRunId != firstExecutionRunID {
				return nil, consts.ErrWorkflowExecutionNotFound
			}

			eventBatchFirstEventID := mutableState.GetNextEventID()
			return updateWorkflowWithoutWorkflowTask, workflow.TerminateWorkflow(
				mutableState,
				eventBatchFirstEventID,
				request.GetReason(),
				request.GetDetails(),
				request.GetIdentity(),
			)
		})
}

// RecordChildExecutionCompleted records the completion of child execution into parent execution history
func (e *historyEngineImpl) RecordChildExecutionCompleted(
	ctx context.Context,
	completionRequest *historyservice.RecordChildExecutionCompletedRequest,
) error {

	namespaceEntry, err := e.getActiveNamespaceEntry(completionRequest.GetNamespaceId())
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id

	execution := commonpb.WorkflowExecution{
		WorkflowId: completionRequest.WorkflowExecution.WorkflowId,
		RunId:      completionRequest.WorkflowExecution.RunId,
	}

	return e.updateWorkflowExecution(
		ctx,
		namespaceID,
		execution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			if !mutableState.IsWorkflowExecutionRunning() {
				return nil, consts.ErrWorkflowCompleted
			}

			initiatedID := completionRequest.InitiatedId
			completedExecution := completionRequest.CompletedExecution
			completionEvent := completionRequest.CompletionEvent

			// Check mutable state to make sure child execution is in pending child executions
			ci, isRunning := mutableState.GetChildExecutionInfo(initiatedID)
			if !isRunning || ci.StartedId == common.EmptyEventID {
				return nil, serviceerror.NewNotFound("Pending child execution not found.")
			}
			if ci.GetStartedWorkflowId() != completedExecution.GetWorkflowId() {
				return nil, serviceerror.NewNotFound("Pending child execution not found.")
			}

			switch completionEvent.GetEventType() {
			case enumspb.EVENT_TYPE_WORKFLOW_EXECUTION_COMPLETED:
				attributes := completionEvent.GetWorkflowExecutionCompletedEventAttributes()
				_, err = mutableState.AddChildWorkflowExecutionCompletedEvent(initiatedID, completedExecution, attributes)
			case enumspb.EVENT_TYPE_WORKFLOW_EXECUTION_FAILED:
				attributes := completionEvent.GetWorkflowExecutionFailedEventAttributes()
				_, err = mutableState.AddChildWorkflowExecutionFailedEvent(initiatedID, completedExecution, attributes)
			case enumspb.EVENT_TYPE_WORKFLOW_EXECUTION_CANCELED:
				attributes := completionEvent.GetWorkflowExecutionCanceledEventAttributes()
				_, err = mutableState.AddChildWorkflowExecutionCanceledEvent(initiatedID, completedExecution, attributes)
			case enumspb.EVENT_TYPE_WORKFLOW_EXECUTION_TERMINATED:
				attributes := completionEvent.GetWorkflowExecutionTerminatedEventAttributes()
				_, err = mutableState.AddChildWorkflowExecutionTerminatedEvent(initiatedID, completedExecution, attributes)
			case enumspb.EVENT_TYPE_WORKFLOW_EXECUTION_TIMED_OUT:
				attributes := completionEvent.GetWorkflowExecutionTimedOutEventAttributes()
				_, err = mutableState.AddChildWorkflowExecutionTimedOutEvent(initiatedID, completedExecution, attributes)
			}

			if err != nil {
				return nil, err
			}
			return &updateWorkflowAction{
				noop:               false,
				createWorkflowTask: true,
			}, err
		})
}

func (e *historyEngineImpl) ReplicateEventsV2(
	ctx context.Context,
	replicateRequest *historyservice.ReplicateEventsV2Request,
) error {

	return e.nDCReplicator.ApplyEvents(ctx, replicateRequest)
}

func (e *historyEngineImpl) SyncShardStatus(
	ctx context.Context,
	request *historyservice.SyncShardStatusRequest,
) error {

	clusterName := request.GetSourceCluster()
	now := timestamp.TimeValue(request.GetStatusTime())

	// here there are 3 main things
	// 1. update the view of remote cluster's shard time
	// 2. notify the timer gate in the timer queue standby processor
	// 3, notify the transfer (essentially a no op, just put it here so it looks symmetric)
	e.shard.SetCurrentTime(clusterName, now)
	e.txProcessor.NotifyNewTask(clusterName, []persistence.Task{})
	e.timerProcessor.NotifyNewTimers(clusterName, []persistence.Task{})
	return nil
}

func (e *historyEngineImpl) SyncActivity(
	ctx context.Context,
	request *historyservice.SyncActivityRequest,
) (retError error) {

	return e.nDCActivityReplicator.SyncActivity(ctx, request)
}

func (e *historyEngineImpl) ResetWorkflowExecution(
	ctx context.Context,
	resetRequest *historyservice.ResetWorkflowExecutionRequest,
) (response *historyservice.ResetWorkflowExecutionResponse, retError error) {

	request := resetRequest.ResetRequest
	namespaceID := resetRequest.GetNamespaceId()
	workflowID := request.WorkflowExecution.GetWorkflowId()
	baseRunID := request.WorkflowExecution.GetRunId()

	baseContext, baseReleaseFn, err := e.historyCache.GetOrCreateWorkflowExecution(
		ctx,
		namespaceID,
		commonpb.WorkflowExecution{
			WorkflowId: workflowID,
			RunId:      baseRunID,
		},
		workflow.CallerTypeAPI,
	)
	if err != nil {
		return nil, err
	}
	defer func() { baseReleaseFn(retError) }()

	baseMutableState, err := baseContext.LoadWorkflowExecution()
	if err != nil {
		return nil, err
	}
	if request.GetWorkflowTaskFinishEventId() <= common.FirstEventID ||
		request.GetWorkflowTaskFinishEventId() >= baseMutableState.GetNextEventID() {
		return nil, serviceerror.NewInvalidArgument("Workflow task finish ID must be > 1 && <= workflow last event ID.")
	}

	switch request.GetResetReapplyType() {
	case enumspb.RESET_REAPPLY_TYPE_UNSPECIFIED:
		return nil, serviceerror.NewInvalidArgument("reset type not set")
	case enumspb.RESET_REAPPLY_TYPE_SIGNAL:
		// noop
	case enumspb.RESET_REAPPLY_TYPE_NONE:
		// noop
	default:
		return nil, serviceerror.NewUnavailable("unknown reset type")
	}

	// also load the current run of the workflow, it can be different from the base runID
	resp, err := e.executionManager.GetCurrentExecution(&persistence.GetCurrentExecutionRequest{
		ShardID:     e.shard.GetShardID(),
		NamespaceID: namespaceID,
		WorkflowID:  request.WorkflowExecution.GetWorkflowId(),
	})
	if err != nil {
		return nil, err
	}

	currentRunID := resp.RunID
	if baseRunID == "" {
		baseRunID = currentRunID
	}

	var currentContext workflow.Context
	var currentMutableState workflow.MutableState
	var currentReleaseFn workflow.ReleaseCacheFunc
	if currentRunID == baseRunID {
		currentContext = baseContext
		currentMutableState = baseMutableState
	} else {
		currentContext, currentReleaseFn, err = e.historyCache.GetOrCreateWorkflowExecution(
			ctx,
			namespaceID,
			commonpb.WorkflowExecution{
				WorkflowId: workflowID,
				RunId:      currentRunID,
			},
			workflow.CallerTypeAPI,
		)
		if err != nil {
			return nil, err
		}
		defer func() { currentReleaseFn(retError) }()

		currentMutableState, err = currentContext.LoadWorkflowExecution()
		if err != nil {
			return nil, err
		}
	}

	// dedup by requestID
	if currentMutableState.GetExecutionState().CreateRequestId == request.GetRequestId() {
		e.logger.Info("Duplicated reset request",
			tag.WorkflowID(workflowID),
			tag.WorkflowRunID(currentRunID),
			tag.WorkflowNamespaceID(namespaceID))
		return &historyservice.ResetWorkflowExecutionResponse{
			RunId: currentRunID,
		}, nil
	}

	resetRunID := uuid.New()
	baseRebuildLastEventID := request.GetWorkflowTaskFinishEventId() - 1
	baseVersionHistories := baseMutableState.GetExecutionInfo().GetVersionHistories()
	baseCurrentVersionHistory, err := versionhistory.GetCurrentVersionHistory(baseVersionHistories)
	if err != nil {
		return nil, err
	}
	baseRebuildLastEventVersion, err := versionhistory.GetVersionHistoryEventVersion(baseCurrentVersionHistory, baseRebuildLastEventID)
	if err != nil {
		return nil, err
	}
	baseCurrentBranchToken := baseCurrentVersionHistory.GetBranchToken()
	baseNextEventID := baseMutableState.GetNextEventID()

	if err := e.workflowResetter.resetWorkflow(
		ctx,
		namespaceID,
		workflowID,
		baseRunID,
		baseCurrentBranchToken,
		baseRebuildLastEventID,
		baseRebuildLastEventVersion,
		baseNextEventID,
		resetRunID,
		request.GetRequestId(),
		newNDCWorkflow(
			ctx,
			e.shard.GetNamespaceCache(),
			e.shard.GetClusterMetadata(),
			currentContext,
			currentMutableState,
			currentReleaseFn,
		),
		request.GetReason(),
		nil,
		request.GetResetReapplyType(),
	); err != nil {
		return nil, err
	}
	return &historyservice.ResetWorkflowExecutionResponse{
		RunId: resetRunID,
	}, nil
}

func (e *historyEngineImpl) updateWorkflow(
	ctx context.Context,
	namespaceID string,
	execution commonpb.WorkflowExecution,
	action updateWorkflowActionFunc,
) (retError error) {

	workflowContext, err := e.loadWorkflow(ctx, namespaceID, execution.GetWorkflowId(), execution.GetRunId())
	if err != nil {
		return err
	}
	defer func() { workflowContext.getReleaseFn()(retError) }()

	return e.updateWorkflowHelper(workflowContext, action)
}

func (e *historyEngineImpl) updateWorkflowExecution(
	ctx context.Context,
	namespaceID string,
	execution commonpb.WorkflowExecution,
	action updateWorkflowActionFunc,
) (retError error) {

	workflowContext, err := e.loadWorkflowOnce(ctx, namespaceID, execution.GetWorkflowId(), execution.GetRunId())
	if err != nil {
		return err
	}
	defer func() { workflowContext.getReleaseFn()(retError) }()

	return e.updateWorkflowHelper(workflowContext, action)
}

func (e *historyEngineImpl) updateWorkflowHelper(
	workflowContext workflowContext,
	action updateWorkflowActionFunc,
) (retError error) {

UpdateHistoryLoop:
	for attempt := 1; attempt <= conditionalRetryCount; attempt++ {
		weContext := workflowContext.getContext()
		mutableState := workflowContext.getMutableState()

		// conduct caller action
		postActions, err := action(weContext, mutableState)
		if err != nil {
			if err == consts.ErrStaleState {
				// Handler detected that cached workflow mutable could potentially be stale
				// Reload workflow execution history
				workflowContext.getContext().Clear()
				if attempt != conditionalRetryCount {
					_, err = workflowContext.reloadMutableState()
					if err != nil {
						return err
					}
				}
				continue UpdateHistoryLoop
			}

			// Returned error back to the caller
			return err
		}
		if postActions.noop {
			return nil
		}

		if postActions.createWorkflowTask {
			// Create a transfer task to schedule a workflow task
			if !mutableState.HasPendingWorkflowTask() {
				_, err := mutableState.AddWorkflowTaskScheduledEvent(false)
				if err != nil {
					return serviceerror.NewUnavailable("Failed to add workflow task scheduled event.")
				}
			}
		}

		err = workflowContext.getContext().UpdateWorkflowExecutionAsActive(e.shard.GetTimeSource().Now())
		if err == consts.ErrConflict {
			if attempt != conditionalRetryCount {
				_, err = workflowContext.reloadMutableState()
				if err != nil {
					return err
				}
			}
			continue UpdateHistoryLoop
		}
		return err
	}
	return consts.ErrMaxAttemptsExceeded
}

func (e *historyEngineImpl) failWorkflowTask(
	context workflow.Context,
	scheduleID int64,
	startedID int64,
	wtFailedCause *workflowTaskFailedCause,
	request *workflowservice.RespondWorkflowTaskCompletedRequest,
) (workflow.MutableState, error) {

	// clear any updates we have accumulated so far
	context.Clear()

	// Reload workflow execution so we can apply the workflow task failure event
	mutableState, err := context.LoadWorkflowExecution()
	if err != nil {
		return nil, err
	}

	if _, err = mutableState.AddWorkflowTaskFailedEvent(
		scheduleID,
		startedID,
		wtFailedCause.failedCause,
		failure.NewServerFailure(wtFailedCause.Message(), true),
		request.GetIdentity(),
		request.GetBinaryChecksum(),
		"",
		"",
		0); err != nil {
		return nil, err
	}

	// Return new builder back to the caller for further updates
	return mutableState, nil
}

func (e *historyEngineImpl) NotifyNewHistoryEvent(
	notification *events.Notification,
) {

	e.eventNotifier.NotifyNewHistoryEvent(notification)
}

func (e *historyEngineImpl) NotifyNewTransferTasks(
	tasks []persistence.Task,
) {

	if len(tasks) > 0 {
		task := tasks[0]
		clusterName := e.clusterMetadata.ClusterNameForFailoverVersion(task.GetVersion())
		e.txProcessor.NotifyNewTask(clusterName, tasks)
	}
}

func (e *historyEngineImpl) NotifyNewTimerTasks(
	tasks []persistence.Task,
) {

	if len(tasks) > 0 {
		task := tasks[0]
		clusterName := e.clusterMetadata.ClusterNameForFailoverVersion(task.GetVersion())
		e.timerProcessor.NotifyNewTimers(clusterName, tasks)
	}
}

func (e *historyEngineImpl) NotifyNewReplicationTasks(
	tasks []persistence.Task,
) {

	if len(tasks) > 0 && e.replicatorProcessor != nil {
		e.replicatorProcessor.NotifyNewTasks(tasks)
	}
}

func (e *historyEngineImpl) NotifyNewVisibilityTasks(
	tasks []persistence.Task,
) {

	if len(tasks) > 0 && e.visibilityProcessor != nil {
		e.visibilityProcessor.NotifyNewTask(tasks)
	}
}

func (e *historyEngineImpl) validateStartWorkflowExecutionRequest(
	ctx context.Context,
	request *workflowservice.StartWorkflowExecutionRequest,
	namespace string,
	operation string,
) error {

	maxIDLengthLimit := e.config.MaxIDLengthLimit()
	blobSizeLimitError := e.config.BlobSizeLimitError(namespace)
	blobSizeLimitWarn := e.config.BlobSizeLimitWarn(namespace)
	memoSizeLimitError := e.config.MemoSizeLimitError(namespace)
	memoSizeLimitWarn := e.config.MemoSizeLimitWarn(namespace)

	if len(request.GetRequestId()) == 0 {
		return serviceerror.NewInvalidArgument("Missing request ID.")
	}
	if timestamp.DurationValue(request.GetWorkflowExecutionTimeout()) < 0 {
		return serviceerror.NewInvalidArgument("Invalid WorkflowExecutionTimeoutSeconds.")
	}
	if timestamp.DurationValue(request.GetWorkflowRunTimeout()) < 0 {
		return serviceerror.NewInvalidArgument("Invalid WorkflowRunTimeoutSeconds.")
	}
	if timestamp.DurationValue(request.GetWorkflowTaskTimeout()) < 0 {
		return serviceerror.NewInvalidArgument("Invalid WorkflowTaskTimeoutSeconds.")
	}
	if request.TaskQueue == nil || request.TaskQueue.GetName() == "" {
		return serviceerror.NewInvalidArgument("Missing Taskqueue.")
	}
	if request.WorkflowType == nil || request.WorkflowType.GetName() == "" {
		return serviceerror.NewInvalidArgument("Missing WorkflowType.")
	}
	if len(request.GetNamespace()) > maxIDLengthLimit {
		return serviceerror.NewInvalidArgument("Namespace exceeds length limit.")
	}
	if len(request.GetWorkflowId()) > maxIDLengthLimit {
		return serviceerror.NewInvalidArgument("WorkflowId exceeds length limit.")
	}
	if len(request.TaskQueue.GetName()) > maxIDLengthLimit {
		return serviceerror.NewInvalidArgument("TaskQueue exceeds length limit.")
	}
	if len(request.WorkflowType.GetName()) > maxIDLengthLimit {
		return serviceerror.NewInvalidArgument("WorkflowType exceeds length limit.")
	}
	if err := common.ValidateRetryPolicy(request.RetryPolicy); err != nil {
		return err
	}
	if err := e.searchAttributesValidator.Validate(request.SearchAttributes, namespace, e.config.DefaultVisibilityIndexName); err != nil {
		return err
	}
	if err := e.searchAttributesValidator.ValidateSize(request.SearchAttributes, namespace); err != nil {
		return err
	}

	if err := common.CheckEventBlobSizeLimit(
		request.GetInput().Size(),
		blobSizeLimitWarn,
		blobSizeLimitError,
		namespace,
		request.GetWorkflowId(),
		"",
		e.metricsScope(ctx).Tagged(metrics.CommandTypeTag(enumspb.COMMAND_TYPE_UNSPECIFIED.String())),
		e.throttledLogger,
		tag.BlobSizeViolationOperation(operation),
	); err != nil {
		return err
	}

	if err := common.CheckEventBlobSizeLimit(
		request.GetMemo().Size(),
		memoSizeLimitWarn,
		memoSizeLimitError,
		namespace,
		request.GetWorkflowId(),
		"",
		e.metricsScope(ctx).Tagged(metrics.CommandTypeTag(enumspb.COMMAND_TYPE_UNSPECIFIED.String())),
		e.throttledLogger,
		tag.BlobSizeViolationOperation(operation),
	); err != nil {
		return err
	}

	return nil
}

func (e *historyEngineImpl) overrideStartWorkflowExecutionRequest(
	request *workflowservice.StartWorkflowExecutionRequest,
	metricsScope int,
) {
	// workflow execution timeout is left as is
	//  if workflow execution timeout == 0 -> infinity

	namespace := request.GetNamespace()

	workflowRunTimeout := common.OverrideWorkflowRunTimeout(
		timestamp.DurationValue(request.GetWorkflowRunTimeout()),
		timestamp.DurationValue(request.GetWorkflowExecutionTimeout()),
	)
	if workflowRunTimeout != timestamp.DurationValue(request.GetWorkflowRunTimeout()) {
		request.WorkflowRunTimeout = timestamp.DurationPtr(workflowRunTimeout)
		e.metricsClient.Scope(
			metricsScope,
			metrics.NamespaceTag(namespace),
		).IncCounter(metrics.WorkflowRunTimeoutOverrideCount)
	}

	workflowTaskStartToCloseTimeout := common.OverrideWorkflowTaskTimeout(
		namespace,
		timestamp.DurationValue(request.GetWorkflowTaskTimeout()),
		timestamp.DurationValue(request.GetWorkflowRunTimeout()),
		e.config.DefaultWorkflowTaskTimeout,
	)
	if workflowTaskStartToCloseTimeout != timestamp.DurationValue(request.GetWorkflowTaskTimeout()) {
		request.WorkflowTaskTimeout = timestamp.DurationPtr(workflowTaskStartToCloseTimeout)
		e.metricsClient.Scope(
			metricsScope,
			metrics.NamespaceTag(namespace),
		).IncCounter(metrics.WorkflowTaskTimeoutOverrideCount)
	}
}

func validateNamespaceUUID(
	namespaceUUID string,
) (string, error) {

	if namespaceUUID == "" {
		return "", serviceerror.NewInvalidArgument("Missing namespace UUID.")
	} else if uuid.Parse(namespaceUUID) == nil {
		return "", serviceerror.NewInvalidArgument("Invalid namespace UUID.")
	}
	return namespaceUUID, nil
}

func (e *historyEngineImpl) getActiveNamespaceEntry(
	namespaceUUID string,
) (*namespace.CacheEntry, error) {

	return getActiveNamespaceEntryFromShard(e.shard, namespaceUUID)
}

func getActiveNamespaceEntryFromShard(
	shard shard.Context,
	namespaceUUID string,
) (*namespace.CacheEntry, error) {

	namespaceID, err := validateNamespaceUUID(namespaceUUID)
	if err != nil {
		return nil, err
	}

	namespaceEntry, err := shard.GetNamespaceCache().GetNamespaceByID(namespaceID)
	if err != nil {
		return nil, err
	}
	if err = namespaceEntry.GetNamespaceNotActiveErr(); err != nil {
		return nil, err
	}
	return namespaceEntry, nil
}

func getScheduleID(
	activityID string,
	mutableState workflow.MutableState,
) (int64, error) {

	if activityID == "" {
		return 0, serviceerror.NewInvalidArgument("Neither ActivityID nor ScheduleID is provided")
	}
	activityInfo, ok := mutableState.GetActivityByActivityID(activityID)
	if !ok {
		return 0, serviceerror.NewInvalidArgument("Cannot locate Activity ScheduleID")
	}
	return activityInfo.ScheduleId, nil
}

func (e *historyEngineImpl) getStartRequest(
	namespaceID string,
	request *workflowservice.SignalWithStartWorkflowExecutionRequest,
) *historyservice.StartWorkflowExecutionRequest {

	req := &workflowservice.StartWorkflowExecutionRequest{
		Namespace:                request.GetNamespace(),
		WorkflowId:               request.GetWorkflowId(),
		WorkflowType:             request.GetWorkflowType(),
		TaskQueue:                request.GetTaskQueue(),
		Input:                    request.GetInput(),
		WorkflowExecutionTimeout: request.GetWorkflowExecutionTimeout(),
		WorkflowRunTimeout:       request.GetWorkflowRunTimeout(),
		WorkflowTaskTimeout:      request.GetWorkflowTaskTimeout(),
		Identity:                 request.GetIdentity(),
		RequestId:                request.GetRequestId(),
		WorkflowIdReusePolicy:    request.GetWorkflowIdReusePolicy(),
		RetryPolicy:              request.GetRetryPolicy(),
		CronSchedule:             request.GetCronSchedule(),
		Memo:                     request.GetMemo(),
		SearchAttributes:         request.GetSearchAttributes(),
		Header:                   request.GetHeader(),
	}

	return common.CreateHistoryStartWorkflowRequest(namespaceID, req, nil, e.shard.GetTimeSource().Now())
}

// for startWorkflowExecution & signalWithStart to handle workflow reuse policy
func (e *historyEngineImpl) applyWorkflowIDReusePolicyForSigWithStart(
	prevExecutionState *persistencespb.WorkflowExecutionState,
	namespaceID string,
	execution commonpb.WorkflowExecution,
	wfIDReusePolicy enumspb.WorkflowIdReusePolicy,
) error {

	prevStartRequestID := prevExecutionState.CreateRequestId
	prevRunID := prevExecutionState.RunId
	prevState := prevExecutionState.State
	prevStatus := prevExecutionState.Status

	return e.applyWorkflowIDReusePolicyHelper(
		prevStartRequestID,
		prevRunID,
		prevState,
		prevStatus,
		namespaceID,
		execution,
		wfIDReusePolicy,
	)

}

func (e *historyEngineImpl) applyWorkflowIDReusePolicyHelper(
	prevStartRequestID,
	prevRunID string,
	prevState enumsspb.WorkflowExecutionState,
	prevStatus enumspb.WorkflowExecutionStatus,
	namespaceID string,
	execution commonpb.WorkflowExecution,
	wfIDReusePolicy enumspb.WorkflowIdReusePolicy,
) error {

	// here we know there is some information about the prev workflow, i.e. either running right now
	// or has history check if the this workflow is finished
	switch prevState {
	case enumsspb.WORKFLOW_EXECUTION_STATE_CREATED,
		enumsspb.WORKFLOW_EXECUTION_STATE_RUNNING:
		msg := "Workflow execution is already running. WorkflowId: %v, RunId: %v."
		return getWorkflowAlreadyStartedError(msg, prevStartRequestID, execution.GetWorkflowId(), prevRunID)
	case enumsspb.WORKFLOW_EXECUTION_STATE_COMPLETED:
		// previous workflow completed, proceed
	default:
		// persistence.WorkflowStateZombie or unknown type
		return serviceerror.NewUnavailable(fmt.Sprintf("Failed to process workflow, workflow has invalid state: %v.", prevState))
	}

	switch wfIDReusePolicy {
	case enumspb.WORKFLOW_ID_REUSE_POLICY_ALLOW_DUPLICATE_FAILED_ONLY:
		if _, ok := consts.FailedWorkflowStatuses[prevStatus]; !ok {
			msg := "Workflow execution already finished successfully. WorkflowId: %v, RunId: %v. Workflow Id reuse policy: allow duplicate workflow Id if last run failed."
			return getWorkflowAlreadyStartedError(msg, prevStartRequestID, execution.GetWorkflowId(), prevRunID)
		}
	case enumspb.WORKFLOW_ID_REUSE_POLICY_ALLOW_DUPLICATE:
		// as long as workflow not running, so this case has no check
	case enumspb.WORKFLOW_ID_REUSE_POLICY_REJECT_DUPLICATE:
		msg := "Workflow execution already finished. WorkflowId: %v, RunId: %v. Workflow Id reuse policy: reject duplicate workflow Id."
		return getWorkflowAlreadyStartedError(msg, prevStartRequestID, execution.GetWorkflowId(), prevRunID)
	default:
		return serviceerror.NewUnavailable(fmt.Sprintf("Failed to process start workflow reuse policy: %v.", wfIDReusePolicy))
	}

	return nil
}

func getWorkflowAlreadyStartedError(errMsg string, createRequestID string, workflowID string, runID string) error {
	return serviceerror.NewWorkflowExecutionAlreadyStarted(
		fmt.Sprintf(errMsg, workflowID, runID),
		createRequestID,
		runID,
	)
}

func (e *historyEngineImpl) GetReplicationMessages(
	ctx context.Context,
	pollingCluster string,
	ackMessageID int64,
	queryMessageID int64,
) (*replicationspb.ReplicationMessages, error) {

	if ackMessageID != persistence.EmptyQueueMessageID {
		if err := e.shard.UpdateClusterReplicationLevel(
			pollingCluster,
			ackMessageID,
		); err != nil {
			e.logger.Error("error updating replication level for shard", tag.Error(err), tag.OperationFailed)
		}
	}

	replicationMessages, err := e.replicatorProcessor.paginateTasks(
		ctx,
		pollingCluster,
		queryMessageID,
	)
	if err != nil {
		e.logger.Error("Failed to retrieve replication messages.", tag.Error(err))
		return nil, err
	}
	e.logger.Debug("Successfully fetched replication messages.", tag.Counter(len(replicationMessages.ReplicationTasks)))
	return replicationMessages, nil
}

func (e *historyEngineImpl) GetDLQReplicationMessages(
	ctx context.Context,
	taskInfos []*replicationspb.ReplicationTaskInfo,
) ([]*replicationspb.ReplicationTask, error) {

	tasks := make([]*replicationspb.ReplicationTask, 0, len(taskInfos))
	for _, taskInfo := range taskInfos {
		task, err := e.replicatorProcessor.getTask(ctx, taskInfo)
		if err != nil {
			e.logger.Error("Failed to fetch DLQ replication messages.", tag.Error(err))
			return nil, err
		}
		tasks = append(tasks, task)
	}

	return tasks, nil
}

func (e *historyEngineImpl) ReapplyEvents(
	ctx context.Context,
	namespaceUUID string,
	workflowID string,
	runID string,
	reapplyEvents []*historypb.HistoryEvent,
) error {

	if e.config.SkipReapplicationByNamespaceID(namespaceUUID) {
		return nil
	}

	namespaceEntry, err := e.getActiveNamespaceEntry(namespaceUUID)
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id
	// remove run id from the execution so that reapply events to the current run
	currentExecution := commonpb.WorkflowExecution{
		WorkflowId: workflowID,
	}

	return e.updateWorkflowExecution(
		ctx,
		namespaceID,
		currentExecution,
		func(context workflow.Context, mutableState workflow.MutableState) (*updateWorkflowAction, error) {
			// Filter out reapply event from the same cluster
			toReapplyEvents := make([]*historypb.HistoryEvent, 0, len(reapplyEvents))
			lastWriteVersion, err := mutableState.GetLastWriteVersion()
			if err != nil {
				return nil, err
			}
			for _, event := range reapplyEvents {
				if event.GetVersion() == lastWriteVersion {
					// The reapply is from the same cluster. Ignoring.
					continue
				}
				dedupResource := definition.NewEventReappliedID(runID, event.GetEventId(), event.GetVersion())
				if mutableState.IsResourceDuplicated(dedupResource) {
					// already apply the signal
					continue
				}
				toReapplyEvents = append(toReapplyEvents, event)
			}
			if len(toReapplyEvents) == 0 {
				return &updateWorkflowAction{
					noop:               true,
					createWorkflowTask: false,
				}, nil
			}

			if !mutableState.IsWorkflowExecutionRunning() {
				// need to reset target workflow (which is also the current workflow)
				// to accept events to be reapplied
				baseRunID := mutableState.GetExecutionState().GetRunId()
				resetRunID := uuid.New()
				baseRebuildLastEventID := mutableState.GetPreviousStartedEventID()

				// TODO when https://github.com/uber/cadence/issues/2420 is finished, remove this block,
				//  since cannot reapply event to a finished workflow which had no workflow tasks started
				if baseRebuildLastEventID == common.EmptyEventID {
					e.logger.Warn("cannot reapply event to a finished workflow",
						tag.WorkflowNamespaceID(namespaceID),
						tag.WorkflowID(currentExecution.GetWorkflowId()),
					)
					e.metricsClient.IncCounter(metrics.HistoryReapplyEventsScope, metrics.EventReapplySkippedCount)
					return &updateWorkflowAction{
						noop:               true,
						createWorkflowTask: false,
					}, nil
				}

				baseVersionHistories := mutableState.GetExecutionInfo().GetVersionHistories()
				baseCurrentVersionHistory, err := versionhistory.GetCurrentVersionHistory(baseVersionHistories)
				if err != nil {
					return nil, err
				}
				baseRebuildLastEventVersion, err := versionhistory.GetVersionHistoryEventVersion(baseCurrentVersionHistory, baseRebuildLastEventID)
				if err != nil {
					return nil, err
				}
				baseCurrentBranchToken := baseCurrentVersionHistory.GetBranchToken()
				baseNextEventID := mutableState.GetNextEventID()

				if err = e.workflowResetter.resetWorkflow(
					ctx,
					namespaceID,
					workflowID,
					baseRunID,
					baseCurrentBranchToken,
					baseRebuildLastEventID,
					baseRebuildLastEventVersion,
					baseNextEventID,
					resetRunID,
					uuid.New(),
					newNDCWorkflow(
						ctx,
						e.shard.GetNamespaceCache(),
						e.shard.GetClusterMetadata(),
						context,
						mutableState,
						workflow.NoopReleaseFn,
					),
					eventsReapplicationResetWorkflowReason,
					toReapplyEvents,
					enumspb.RESET_REAPPLY_TYPE_SIGNAL,
				); err != nil {
					return nil, err
				}
				return &updateWorkflowAction{
					noop:               true,
					createWorkflowTask: false,
				}, nil
			}

			postActions := &updateWorkflowAction{
				noop:               false,
				createWorkflowTask: true,
			}
			// Do not create workflow task when the workflow is cron and the cron has not been started yet
			if mutableState.GetExecutionInfo().CronSchedule != "" && !mutableState.HasProcessedOrPendingWorkflowTask() {
				postActions.createWorkflowTask = false
			}
			reappliedEvents, err := e.eventsReapplier.reapplyEvents(
				ctx,
				mutableState,
				toReapplyEvents,
				runID,
			)
			if err != nil {
				e.logger.Error("failed to re-apply stale events", tag.Error(err))
				return nil, serviceerror.NewUnavailable("unable to re-apply stale events")
			}
			if len(reappliedEvents) == 0 {
				return &updateWorkflowAction{
					noop:               true,
					createWorkflowTask: false,
				}, nil
			}
			return postActions, nil
		})
}

func (e *historyEngineImpl) GetDLQMessages(
	ctx context.Context,
	request *historyservice.GetDLQMessagesRequest,
) (*historyservice.GetDLQMessagesResponse, error) {

	_, ok := e.clusterMetadata.GetAllClusterInfo()[request.GetSourceCluster()]
	if !ok {
		return nil, consts.ErrUnknownCluster
	}

	tasks, token, err := e.replicationDLQHandler.getMessages(
		ctx,
		request.GetSourceCluster(),
		request.GetInclusiveEndMessageId(),
		int(request.GetMaximumPageSize()),
		request.GetNextPageToken(),
	)
	if err != nil {
		return nil, err
	}
	return &historyservice.GetDLQMessagesResponse{
		Type:             request.GetType(),
		ReplicationTasks: tasks,
		NextPageToken:    token,
	}, nil
}

func (e *historyEngineImpl) PurgeDLQMessages(
	ctx context.Context,
	request *historyservice.PurgeDLQMessagesRequest,
) error {

	_, ok := e.clusterMetadata.GetAllClusterInfo()[request.GetSourceCluster()]
	if !ok {
		return consts.ErrUnknownCluster
	}

	return e.replicationDLQHandler.purgeMessages(
		request.GetSourceCluster(),
		request.GetInclusiveEndMessageId(),
	)
}

func (e *historyEngineImpl) MergeDLQMessages(
	ctx context.Context,
	request *historyservice.MergeDLQMessagesRequest,
) (*historyservice.MergeDLQMessagesResponse, error) {

	_, ok := e.clusterMetadata.GetAllClusterInfo()[request.GetSourceCluster()]
	if !ok {
		return nil, consts.ErrUnknownCluster
	}

	token, err := e.replicationDLQHandler.mergeMessages(
		ctx,
		request.GetSourceCluster(),
		request.GetInclusiveEndMessageId(),
		int(request.GetMaximumPageSize()),
		request.GetNextPageToken(),
	)
	if err != nil {
		return nil, err
	}
	return &historyservice.MergeDLQMessagesResponse{
		NextPageToken: token,
	}, nil
}

func (e *historyEngineImpl) RefreshWorkflowTasks(
	ctx context.Context,
	namespaceUUID string,
	execution commonpb.WorkflowExecution,
) (retError error) {

	namespaceEntry, err := e.getActiveNamespaceEntry(namespaceUUID)
	if err != nil {
		return err
	}
	namespaceID := namespaceEntry.GetInfo().Id

	context, release, err := e.historyCache.GetOrCreateWorkflowExecution(
		ctx,
		namespaceID,
		execution,
		workflow.CallerTypeAPI,
	)
	if err != nil {
		return err
	}
	defer func() { release(retError) }()

	mutableState, err := context.LoadWorkflowExecution()
	if err != nil {
		return err
	}

	if !mutableState.IsWorkflowExecutionRunning() {
		return nil
	}

	mutableStateTaskRefresher := workflow.NewTaskRefresher(
		e.shard.GetConfig(),
		e.shard.GetNamespaceCache(),
		e.shard.GetEventsCache(),
		e.shard.GetLogger(),
	)

	now := e.shard.GetTimeSource().Now()

	err = mutableStateTaskRefresher.RefreshTasks(now, mutableState)
	if err != nil {
		return err
	}

	err = context.UpdateWorkflowExecutionAsActive(now)
	if err != nil {
		return err
	}
	return nil
}

func (e *historyEngineImpl) loadWorkflowOnce(
	ctx context.Context,
	namespaceID string,
	workflowID string,
	runID string,
) (workflowContext, error) {

	context, release, err := e.historyCache.GetOrCreateWorkflowExecution(
		ctx,
		namespaceID,
		commonpb.WorkflowExecution{
			WorkflowId: workflowID,
			RunId:      runID,
		},
		workflow.CallerTypeAPI,
	)
	if err != nil {
		return nil, err
	}

	mutableState, err := context.LoadWorkflowExecution()
	if err != nil {
		release(err)
		return nil, err
	}

	return newWorkflowContext(context, release, mutableState), nil
}

func (e *historyEngineImpl) loadWorkflow(
	ctx context.Context,
	namespaceID string,
	workflowID string,
	runID string,
) (workflowContext, error) {

	if runID != "" {
		return e.loadWorkflowOnce(ctx, namespaceID, workflowID, runID)
	}

	for attempt := 1; attempt <= conditionalRetryCount; attempt++ {

		workflowContext, err := e.loadWorkflowOnce(ctx, namespaceID, workflowID, "")
		if err != nil {
			return nil, err
		}

		if workflowContext.getMutableState().IsWorkflowExecutionRunning() {
			return workflowContext, nil
		}

		// workflow not running, need to check current record
		resp, err := e.shard.GetExecutionManager().GetCurrentExecution(
			&persistence.GetCurrentExecutionRequest{
				ShardID:     e.shard.GetShardID(),
				NamespaceID: namespaceID,
				WorkflowID:  workflowID,
			},
		)
		if err != nil {
			workflowContext.getReleaseFn()(err)
			return nil, err
		}

		if resp.RunID == workflowContext.getRunID() {
			return workflowContext, nil
		}
		workflowContext.getReleaseFn()(nil)
	}

	return nil, serviceerror.NewUnavailable("unable to locate current workflow execution")
}

func (e *historyEngineImpl) metricsScope(ctx context.Context) metrics.Scope {
	return interceptor.MetricsScope(ctx, e.logger)
}

How do you decide when to directly return the error and when to wrap it in serviceerror.NewInternal?