text: /*-------------------------------------------------------------------------
   *
   * execParallel.c
   *	  Support routines for parallel execution.
   *
   * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
   * Portions Copyright (c) 1994, Regents of the University of California
   *
   * This file contains routines that are intended to support setting up,
   * using, and tearing down a ParallelContext from within the PostgreSQL
   * executor.  The ParallelContext machinery will handle starting the
   * workers and ensuring that their state generally matches that of the
   * leader; see src/backend/access/transam/README.parallel for details.
   * However, we must save and restore relevant executor state, such as
   * any ParamListInfo associated with the query, buffer/WAL usage info, and
   * the actual plan to be passed down to the worker.
   *
   * IDENTIFICATION
   *	  src/backend/executor/execParallel.c
   *
   *-------------------------------------------------------------------------
   */
  
  #include "postgres.h"
  
  #include "executor/execParallel.h"
  #include "executor/executor.h"
  #include "executor/nodeAppend.h"
  #include "executor/nodeBitmapHeapscan.h"
  #include "executor/nodeCustom.h"
  #include "executor/nodeForeignscan.h"
  #include "executor/nodeHash.h"
  #include "executor/nodeHashjoin.h"
  #include "executor/nodeIndexonlyscan.h"
  #include "executor/nodeIndexscan.h"
  #include "executor/nodeSeqscan.h"
  #include "executor/nodeSort.h"
  #include "executor/nodeSubplan.h"
  #include "executor/tqueue.h"
  #include "jit/jit.h"
  #include "nodes/nodeFuncs.h"
  #include "pgstat.h"
  #include "storage/spin.h"
  #include "tcop/tcopprot.h"
  #include "utils/datum.h"
  #include "utils/dsa.h"
  #include "utils/lsyscache.h"
  #include "utils/memutils.h"
  #include "utils/snapmgr.h"
  
  /*
   * Magic numbers for parallel executor communication.  We use constants
   * greater than any 32-bit integer here so that values < 2^32 can be used
   * by individual parallel nodes to store their own state.
   */
  #define PARALLEL_KEY_EXECUTOR_FIXED		UINT64CONST(0xE000000000000001)
  #define PARALLEL_KEY_PLANNEDSTMT		UINT64CONST(0xE000000000000002)
  #define PARALLEL_KEY_PARAMLISTINFO		UINT64CONST(0xE000000000000003)
  #define PARALLEL_KEY_BUFFER_USAGE		UINT64CONST(0xE000000000000004)
  #define PARALLEL_KEY_TUPLE_QUEUE		UINT64CONST(0xE000000000000005)
  #define PARALLEL_KEY_INSTRUMENTATION	UINT64CONST(0xE000000000000006)
  #define PARALLEL_KEY_DSA				UINT64CONST(0xE000000000000007)
  #define PARALLEL_KEY_QUERY_TEXT		UINT64CONST(0xE000000000000008)
  #define PARALLEL_KEY_JIT_INSTRUMENTATION UINT64CONST(0xE000000000000009)
  #define PARALLEL_KEY_WAL_USAGE			UINT64CONST(0xE00000000000000A)
  
  #define PARALLEL_TUPLE_QUEUE_SIZE		65536
  
  /*
   * Fixed-size random stuff that we need to pass to parallel workers.
   */
  typedef struct FixedParallelExecutorState
  {
  	int64		tuples_needed;	/* tuple bound, see ExecSetTupleBound */
  	dsa_pointer param_exec;
  	int			eflags;
  	int			jit_flags;
  } FixedParallelExecutorState;
  
  /*
   * DSM structure for accumulating per-PlanState instrumentation.
   *
   * instrument_options: Same meaning here as in instrument.c.
   *
   * instrument_offset: Offset, relative to the start of this structure,
   * of the first Instrumentation object.  This will depend on the length of
   * the plan_node_id array.
   *
   * num_workers: Number of workers.
   *
   * num_plan_nodes: Number of plan nodes.
   *
   * plan_node_id: Array of plan nodes for which we are gathering instrumentation
   * from parallel workers.  The length of this array is given by num_plan_nodes.
   */
  struct SharedExecutorInstrumentation
  {
  	int			instrument_options;
  	int			instrument_offset;
  	int			num_workers;
  	int			num_plan_nodes;
  	int			plan_node_id[FLEXIBLE_ARRAY_MEMBER];
  	/* array of num_plan_nodes * num_workers Instrumentation objects follows */
  };
  #define GetInstrumentationArray(sei) \
  	(AssertVariableIsOfTypeMacro(sei, SharedExecutorInstrumentation *), \
  	 (Instrumentation *) (((char *) sei) + sei->instrument_offset))
  
  /* Context object for ExecParallelEstimate. */
  typedef struct ExecParallelEstimateContext
  {
  	ParallelContext *pcxt;
  	int			nnodes;
  } ExecParallelEstimateContext;
  
  /* Context object for ExecParallelInitializeDSM. */
  typedef struct ExecParallelInitializeDSMContext
  {
  	ParallelContext *pcxt;
  	SharedExecutorInstrumentation *instrumentation;
  	int			nnodes;
  } ExecParallelInitializeDSMContext;
  
  /* Helper functions that run in the parallel leader. */
  static char *ExecSerializePlan(Plan *plan, EState *estate);
  static bool ExecParallelEstimate(PlanState *node,
  								 ExecParallelEstimateContext *e);
  static bool ExecParallelInitializeDSM(PlanState *node,
  									  ExecParallelInitializeDSMContext *d);
  static shm_mq_handle **ExecParallelSetupTupleQueues(ParallelContext *pcxt,
  													bool reinitialize);
  static bool ExecParallelReInitializeDSM(PlanState *planstate,
  										ParallelContext *pcxt);
  static bool ExecParallelRetrieveInstrumentation(PlanState *planstate,
  												SharedExecutorInstrumentation *instrumentation);
  
  /* Helper function that runs in the parallel worker. */
  static DestReceiver *ExecParallelGetReceiver(dsm_segment *seg, shm_toc *toc);
  
  /*
   * Create a serialized representation of the plan to be sent to each worker.
   */
  static char *
  ExecSerializePlan(Plan *plan, EState *estate)
  {
  	PlannedStmt *pstmt;
  	ListCell   *lc;
  
  	/* We can't scribble on the original plan, so make a copy. */
  	plan = copyObject(plan);
  
  	/*
  	 * The worker will start its own copy of the executor, and that copy will
  	 * insert a junk filter if the toplevel node has any resjunk entries. We
  	 * don't want that to happen, because while resjunk columns shouldn't be
  	 * sent back to the user, here the tuples are coming back to another
  	 * backend which may very well need them.  So mutate the target list
  	 * accordingly.  This is sort of a hack; there might be better ways to do
  	 * this...
  	 */
  	foreach(lc, plan->targetlist)
  	{
  		TargetEntry *tle = lfirst_node(TargetEntry, lc);
  
  		tle->resjunk = false;
  	}
  
  	/*
  	 * Create a dummy PlannedStmt.  Most of the fields don't need to be valid
  	 * for our purposes, but the worker will need at least a minimal
  	 * PlannedStmt to start the executor.
  	 */
  	pstmt = makeNode(PlannedStmt);
  	pstmt->commandType = CMD_SELECT;
  	pstmt->queryId = UINT64CONST(0);
  	pstmt->hasReturning = false;
  	pstmt->hasModifyingCTE = false;
  	pstmt->canSetTag = true;
  	pstmt->transientPlan = false;
  	pstmt->dependsOnRole = false;
  	pstmt->parallelModeNeeded = false;
  	pstmt->planTree = plan;
  	pstmt->rtable = estate->es_range_table;
  	pstmt->resultRelations = NIL;
  	pstmt->rootResultRelations = NIL;
  	pstmt->appendRelations = NIL;
  
  	/*
  	 * Transfer only parallel-safe subplans, leaving a NULL "hole" in the list
  	 * for unsafe ones (so that the list indexes of the safe ones are
  	 * preserved).  This positively ensures that the worker won't try to run,
  	 * or even do ExecInitNode on, an unsafe subplan.  That's important to
  	 * protect, eg, non-parallel-aware FDWs from getting into trouble.
  	 */
  	pstmt->subplans = NIL;
  	foreach(lc, estate->es_plannedstmt->subplans)
  	{
  		Plan	   *subplan = (Plan *) lfirst(lc);
  
  		if (subplan && !subplan->parallel_safe)
  			subplan = NULL;
  		pstmt->subplans = lappend(pstmt->subplans, subplan);
  	}
  
  	pstmt->rewindPlanIDs = NULL;
  	pstmt->rowMarks = NIL;
  	pstmt->relationOids = NIL;
  	pstmt->invalItems = NIL;	/* workers can't replan anyway... */
  	pstmt->paramExecTypes = estate->es_plannedstmt->paramExecTypes;
  	pstmt->utilityStmt = NULL;
  	pstmt->stmt_location = -1;
  	pstmt->stmt_len = -1;
  
  	/* Return serialized copy of our dummy PlannedStmt. */
  	return nodeToString(pstmt);
  }
  
  /*
   * Parallel-aware plan nodes (and occasionally others) may need some state
   * which is shared across all parallel workers.  Before we size the DSM, give
   * them a chance to call shm_toc_estimate_chunk or shm_toc_estimate_keys on
   * &pcxt->estimator.
   *
   * While we're at it, count the number of PlanState nodes in the tree, so
   * we know how many Instrumentation structures we need.
   */
  static bool
  ExecParallelEstimate(PlanState *planstate, ExecParallelEstimateContext *e)
  {
  	if (planstate == NULL)
  		return false;
  
  	/* Count this node. */
  	e->nnodes++;
  
  	switch (nodeTag(planstate))
  	{
  		case T_SeqScanState:
  			if (planstate->plan->parallel_aware)
  				ExecSeqScanEstimate((SeqScanState *) planstate,
  									e->pcxt);
  			break;
  		case T_IndexScanState:
  			if (planstate->plan->parallel_aware)
  				ExecIndexScanEstimate((IndexScanState *) planstate,
  									  e->pcxt);
  			break;
  		case T_IndexOnlyScanState:
  			if (planstate->plan->parallel_aware)
  				ExecIndexOnlyScanEstimate((IndexOnlyScanState *) planstate,
  										  e->pcxt);
  			break;
  		case T_ForeignScanState:
  			if (planstate->plan->parallel_aware)
  				ExecForeignScanEstimate((ForeignScanState *) planstate,
  										e->pcxt);
  			break;
  		case T_AppendState:
  			if (planstate->plan->parallel_aware)
  				ExecAppendEstimate((AppendState *) planstate,
  								   e->pcxt);
  			break;
  		case T_CustomScanState:
  			if (planstate->plan->parallel_aware)
  				ExecCustomScanEstimate((CustomScanState *) planstate,
  									   e->pcxt);
  			break;
  		case T_BitmapHeapScanState:
  			if (planstate->plan->parallel_aware)
  				ExecBitmapHeapEstimate((BitmapHeapScanState *) planstate,
  									   e->pcxt);
  			break;
  		case T_HashJoinState:
  			if (planstate->plan->parallel_aware)
  				ExecHashJoinEstimate((HashJoinState *) planstate,
  									 e->pcxt);
  			break;
  		case T_HashState:
  			/* even when not parallel-aware, for EXPLAIN ANALYZE */
  			ExecHashEstimate((HashState *) planstate, e->pcxt);
  			break;
  		case T_SortState:
  			/* even when not parallel-aware, for EXPLAIN ANALYZE */
  			ExecSortEstimate((SortState *) planstate, e->pcxt);
  			break;
  
  		default:
  			break;
  	}
  
  	return planstate_tree_walker(planstate, ExecParallelEstimate, e);
  }
  
  /*
   * Estimate the amount of space required to serialize the indicated parameters.
   */
  static Size
  EstimateParamExecSpace(EState *estate, Bitmapset *params)
  {
  	int			paramid;
  	Size		sz = sizeof(int);
  
  	paramid = -1;
  	while ((paramid = bms_next_member(params, paramid)) >= 0)
  	{
  		Oid			typeOid;
  		int16		typLen;
  		bool		typByVal;
  		ParamExecData *prm;
  
  		prm = &(estate->es_param_exec_vals[paramid]);
  		typeOid = list_nth_oid(estate->es_plannedstmt->paramExecTypes,
  							   paramid);
  
  		sz = add_size(sz, sizeof(int)); /* space for paramid */
  
  		/* space for datum/isnull */
  		if (OidIsValid(typeOid))
  			get_typlenbyval(typeOid, &typLen, &typByVal);
  		else
  		{
  			/* If no type OID, assume by-value, like copyParamList does. */
  			typLen = sizeof(Datum);
  			typByVal = true;
  		}
  		sz = add_size(sz,
  					  datumEstimateSpace(prm->value, prm->isnull,
  										 typByVal, typLen));
  	}
  	return sz;
  }
  
  /*
   * Serialize specified PARAM_EXEC parameters.
   *
   * We write the number of parameters first, as a 4-byte integer, and then
   * write details for each parameter in turn.  The details for each parameter
   * consist of a 4-byte paramid (location of param in execution time internal
   * parameter array) and then the datum as serialized by datumSerialize().
   */
  static dsa_pointer
  SerializeParamExecParams(EState *estate, Bitmapset *params, dsa_area *area)
  {
  	Size		size;
  	int			nparams;
  	int			paramid;
  	ParamExecData *prm;
  	dsa_pointer handle;
  	char	   *start_address;
  
  	/* Allocate enough space for the current parameter values. */
  	size = EstimateParamExecSpace(estate, params);
  	handle = dsa_allocate(area, size);
  	start_address = dsa_get_address(area, handle);
  
  	/* First write the number of parameters as a 4-byte integer. */
  	nparams = bms_num_members(params);
  	memcpy(start_address, &nparams, sizeof(int));
  	start_address += sizeof(int);
  
  	/* Write details for each parameter in turn. */
  	paramid = -1;
  	while ((paramid = bms_next_member(params, paramid)) >= 0)
  	{
  		Oid			typeOid;
  		int16		typLen;
  		bool		typByVal;
  
  		prm = &(estate->es_param_exec_vals[paramid]);
  		typeOid = list_nth_oid(estate->es_plannedstmt->paramExecTypes,
  							   paramid);
  
  		/* Write paramid. */
  		memcpy(start_address, &paramid, sizeof(int));
  		start_address += sizeof(int);
  
  		/* Write datum/isnull */
  		if (OidIsValid(typeOid))
  			get_typlenbyval(typeOid, &typLen, &typByVal);
  		else
  		{
  			/* If no type OID, assume by-value, like copyParamList does. */
  			typLen = sizeof(Datum);
  			typByVal = true;
  		}
  		datumSerialize(prm->value, prm->isnull, typByVal, typLen,
  					   &start_address);
  	}
  
  	return handle;
  }
  
  /*
   * Restore specified PARAM_EXEC parameters.
   */
  static void
  RestoreParamExecParams(char *start_address, EState *estate)
  {
  	int			nparams;
  	int			i;
  	int			paramid;
  
  	memcpy(&nparams, start_address, sizeof(int));
  	start_address += sizeof(int);
  
  	for (i = 0; i < nparams; i++)
  	{
  		ParamExecData *prm;
  
  		/* Read paramid */
  		memcpy(&paramid, start_address, sizeof(int));
  		start_address += sizeof(int);
  		prm = &(estate->es_param_exec_vals[paramid]);
  
  		/* Read datum/isnull. */
  		prm->value = datumRestore(&start_address, &prm->isnull);
  		prm->execPlan = NULL;
  	}
  }
  
  /*
   * Initialize the dynamic shared memory segment that will be used to control
   * parallel execution.
   */
  static bool
  ExecParallelInitializeDSM(PlanState *planstate,
  						  ExecParallelInitializeDSMContext *d)
  {
  	if (planstate == NULL)
  		return false;
  
  	/* If instrumentation is enabled, initialize slot for this node. */
  	if (d->instrumentation != NULL)
  		d->instrumentation->plan_node_id[d->nnodes] =
  			planstate->plan->plan_node_id;
  
  	/* Count this node. */
  	d->nnodes++;
  
  	/*
  	 * Call initializers for DSM-using plan nodes.
  	 *
  	 * Most plan nodes won't do anything here, but plan nodes that allocated
  	 * DSM may need to initialize shared state in the DSM before parallel
  	 * workers are launched.  They can allocate the space they previously
  	 * estimated using shm_toc_allocate, and add the keys they previously
  	 * estimated using shm_toc_insert, in each case targeting pcxt->toc.
  	 */
  	switch (nodeTag(planstate))
  	{
  		case T_SeqScanState:
  			if (planstate->plan->parallel_aware)
  				ExecSeqScanInitializeDSM((SeqScanState *) planstate,
  										 d->pcxt);
  			break;
  		case T_IndexScanState:
  			if (planstate->plan->parallel_aware)
  				ExecIndexScanInitializeDSM((IndexScanState *) planstate,
  										   d->pcxt);
  			break;
  		case T_IndexOnlyScanState:
  			if (planstate->plan->parallel_aware)
  				ExecIndexOnlyScanInitializeDSM((IndexOnlyScanState *) planstate,
  											   d->pcxt);
  			break;
  		case T_ForeignScanState:
  			if (planstate->plan->parallel_aware)
  				ExecForeignScanInitializeDSM((ForeignScanState *) planstate,
  											 d->pcxt);
  			break;
  		case T_AppendState:
  			if (planstate->plan->parallel_aware)
  				ExecAppendInitializeDSM((AppendState *) planstate,
  										d->pcxt);
  			break;
  		case T_CustomScanState:
  			if (planstate->plan->parallel_aware)
  				ExecCustomScanInitializeDSM((CustomScanState *) planstate,
  											d->pcxt);
  			break;
  		case T_BitmapHeapScanState:
  			if (planstate->plan->parallel_aware)
  				ExecBitmapHeapInitializeDSM((BitmapHeapScanState *) planstate,
  											d->pcxt);
  			break;
  		case T_HashJoinState:
  			if (planstate->plan->parallel_aware)
  				ExecHashJoinInitializeDSM((HashJoinState *) planstate,
  										  d->pcxt);
  			break;
  		case T_HashState:
  			/* even when not parallel-aware, for EXPLAIN ANALYZE */
  			ExecHashInitializeDSM((HashState *) planstate, d->pcxt);
  			break;
  		case T_SortState:
  			/* even when not parallel-aware, for EXPLAIN ANALYZE */
  			ExecSortInitializeDSM((SortState *) planstate, d->pcxt);
  			break;
  
  		default:
  			break;
  	}
  
  	return planstate_tree_walker(planstate, ExecParallelInitializeDSM, d);
  }
  
  /*
   * It sets up the response queues for backend workers to return tuples
   * to the main backend and start the workers.
   */
  static shm_mq_handle **
  ExecParallelSetupTupleQueues(ParallelContext *pcxt, bool reinitialize)
  {
  	shm_mq_handle **responseq;
  	char	   *tqueuespace;
  	int			i;
  
  	/* Skip this if no workers. */
  	if (pcxt->nworkers == 0)
  		return NULL;
  
  	/* Allocate memory for shared memory queue handles. */
  	responseq = (shm_mq_handle **)
  		palloc(pcxt->nworkers * sizeof(shm_mq_handle *));
  
  	/*
  	 * If not reinitializing, allocate space from the DSM for the queues;
  	 * otherwise, find the already allocated space.
  	 */
  	if (!reinitialize)
  		tqueuespace =
  			shm_toc_allocate(pcxt->toc,
  							 mul_size(PARALLEL_TUPLE_QUEUE_SIZE,
  									  pcxt->nworkers));
  	else
  		tqueuespace = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_TUPLE_QUEUE, false);
  
  	/* Create the queues, and become the receiver for each. */
  	for (i = 0; i < pcxt->nworkers; ++i)
  	{
  		shm_mq	   *mq;
  
  		mq = shm_mq_create(tqueuespace +
  						   ((Size) i) * PARALLEL_TUPLE_QUEUE_SIZE,
  						   (Size) PARALLEL_TUPLE_QUEUE_SIZE);
  
  		shm_mq_set_receiver(mq, MyProc);
  		responseq[i] = shm_mq_attach(mq, pcxt->seg, NULL);
  	}
  
  	/* Add array of queues to shm_toc, so others can find it. */
  	if (!reinitialize)
  		shm_toc_insert(pcxt->toc, PARALLEL_KEY_TUPLE_QUEUE, tqueuespace);
  
  	/* Return array of handles. */
  	return responseq;
  }
  
  /*
   * Sets up the required infrastructure for backend workers to perform
   * execution and return results to the main backend.
   */
  ParallelExecutorInfo *
  ExecInitParallelPlan(PlanState *planstate, EState *estate,
  					 Bitmapset *sendParams, int nworkers,
  					 int64 tuples_needed)
  {
  	ParallelExecutorInfo *pei;
  	ParallelContext *pcxt;
  	ExecParallelEstimateContext e;
  	ExecParallelInitializeDSMContext d;
  	FixedParallelExecutorState *fpes;
  	char	   *pstmt_data;
  	char	   *pstmt_space;
  	char	   *paramlistinfo_space;
  	BufferUsage *bufusage_space;
  	WalUsage   *walusage_space;
  	SharedExecutorInstrumentation *instrumentation = NULL;
  	SharedJitInstrumentation *jit_instrumentation = NULL;
  	int			pstmt_len;
  	int			paramlistinfo_len;
  	int			instrumentation_len = 0;
  	int			jit_instrumentation_len = 0;
  	int			instrument_offset = 0;
  	Size		dsa_minsize = dsa_minimum_size();
  	char	   *query_string;
  	int			query_len;
  
  	/*
  	 * Force any initplan outputs that we're going to pass to workers to be
  	 * evaluated, if they weren't already.
  	 *
  	 * For simplicity, we use the EState's per-output-tuple ExprContext here.
  	 * That risks intra-query memory leakage, since we might pass through here
  	 * many times before that ExprContext gets reset; but ExecSetParamPlan
  	 * doesn't normally leak any memory in the context (see its comments), so
  	 * it doesn't seem worth complicating this function's API to pass it a
  	 * shorter-lived ExprContext.  This might need to change someday.
  	 */
  	ExecSetParamPlanMulti(sendParams, GetPerTupleExprContext(estate));
  
  	/* Allocate object for return value. */
  	pei = palloc0(sizeof(ParallelExecutorInfo));
  	pei->finished = false;
  	pei->planstate = planstate;
  
  	/* Fix up and serialize plan to be sent to workers. */
  	pstmt_data = ExecSerializePlan(planstate->plan, estate);
  
  	/* Create a parallel context. */
  	pcxt = CreateParallelContext("postgres", "ParallelQueryMain", nworkers);
  	pei->pcxt = pcxt;
  
  	/*
  	 * Before telling the parallel context to create a dynamic shared memory
  	 * segment, we need to figure out how big it should be.  Estimate space
  	 * for the various things we need to store.
  	 */
  
  	/* Estimate space for fixed-size state. */
  	shm_toc_estimate_chunk(&pcxt->estimator,
  						   sizeof(FixedParallelExecutorState));
  	shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  	/* Estimate space for query text. */
  	query_len = strlen(estate->es_sourceText);
  	shm_toc_estimate_chunk(&pcxt->estimator, query_len + 1);
  	shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  	/* Estimate space for serialized PlannedStmt. */
  	pstmt_len = strlen(pstmt_data) + 1;
  	shm_toc_estimate_chunk(&pcxt->estimator, pstmt_len);
  	shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  	/* Estimate space for serialized ParamListInfo. */
  	paramlistinfo_len = EstimateParamListSpace(estate->es_param_list_info);
  	shm_toc_estimate_chunk(&pcxt->estimator, paramlistinfo_len);
  	shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  	/*
  	 * Estimate space for BufferUsage.
  	 *
  	 * If EXPLAIN is not in use and there are no extensions loaded that care,
  	 * we could skip this.  But we have no way of knowing whether anyone's
  	 * looking at pgBufferUsage, so do it unconditionally.
  	 */
  	shm_toc_estimate_chunk(&pcxt->estimator,
  						   mul_size(sizeof(BufferUsage), pcxt->nworkers));
  	shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  	/*
  	 * Same thing for WalUsage.
  	 */
  	shm_toc_estimate_chunk(&pcxt->estimator,
  						   mul_size(sizeof(WalUsage), pcxt->nworkers));
  	shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  	/* Estimate space for tuple queues. */
  	shm_toc_estimate_chunk(&pcxt->estimator,
  						   mul_size(PARALLEL_TUPLE_QUEUE_SIZE, pcxt->nworkers));
  	shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  	/*
  	 * Give parallel-aware nodes a chance to add to the estimates, and get a
  	 * count of how many PlanState nodes there are.
  	 */
  	e.pcxt = pcxt;
  	e.nnodes = 0;
  	ExecParallelEstimate(planstate, &e);
  
  	/* Estimate space for instrumentation, if required. */
  	if (estate->es_instrument)
  	{
  		instrumentation_len =
  			offsetof(SharedExecutorInstrumentation, plan_node_id) +
  			sizeof(int) * e.nnodes;
  		instrumentation_len = MAXALIGN(instrumentation_len);
  		instrument_offset = instrumentation_len;
  		instrumentation_len +=
  			mul_size(sizeof(Instrumentation),
  					 mul_size(e.nnodes, nworkers));
  		shm_toc_estimate_chunk(&pcxt->estimator, instrumentation_len);
  		shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  		/* Estimate space for JIT instrumentation, if required. */
  		if (estate->es_jit_flags != PGJIT_NONE)
  		{
  			jit_instrumentation_len =
  				offsetof(SharedJitInstrumentation, jit_instr) +
  				sizeof(JitInstrumentation) * nworkers;
  			shm_toc_estimate_chunk(&pcxt->estimator, jit_instrumentation_len);
  			shm_toc_estimate_keys(&pcxt->estimator, 1);
  		}
  	}
  
  	/* Estimate space for DSA area. */
  	shm_toc_estimate_chunk(&pcxt->estimator, dsa_minsize);
  	shm_toc_estimate_keys(&pcxt->estimator, 1);
  
  	/* Everyone's had a chance to ask for space, so now create the DSM. */
  	InitializeParallelDSM(pcxt);
  
  	/*
  	 * OK, now we have a dynamic shared memory segment, and it should be big
  	 * enough to store all of the data we estimated we would want to put into
  	 * it, plus whatever general stuff (not specifically executor-related) the
  	 * ParallelContext itself needs to store there.  None of the space we
  	 * asked for has been allocated or initialized yet, though, so do that.
  	 */
  
  	/* Store fixed-size state. */
  	fpes = shm_toc_allocate(pcxt->toc, sizeof(FixedParallelExecutorState));
  	fpes->tuples_needed = tuples_needed;
  	fpes->param_exec = InvalidDsaPointer;
  	fpes->eflags = estate->es_top_eflags;
  	fpes->jit_flags = estate->es_jit_flags;
  	shm_toc_insert(pcxt->toc, PARALLEL_KEY_EXECUTOR_FIXED, fpes);
  
  	/* Store query string */
  	query_string = shm_toc_allocate(pcxt->toc, query_len + 1);
  	memcpy(query_string, estate->es_sourceText, query_len + 1);
  	shm_toc_insert(pcxt->toc, PARALLEL_KEY_QUERY_TEXT, query_string);
  
  	/* Store serialized PlannedStmt. */
  	pstmt_space = shm_toc_allocate(pcxt->toc, pstmt_len);
  	memcpy(pstmt_space, pstmt_data, pstmt_len);
  	shm_toc_insert(pcxt->toc, PARALLEL_KEY_PLANNEDSTMT, pstmt_space);
  
  	/* Store serialized ParamListInfo. */
  	paramlistinfo_space = shm_toc_allocate(pcxt->toc, paramlistinfo_len);
  	shm_toc_insert(pcxt->toc, PARALLEL_KEY_PARAMLISTINFO, paramlistinfo_space);
  	SerializeParamList(estate->es_param_list_info, &paramlistinfo_space);
  
  	/* Allocate space for each worker's BufferUsage; no need to initialize. */
  	bufusage_space = shm_toc_allocate(pcxt->toc,
  									  mul_size(sizeof(BufferUsage), pcxt->nworkers));
  	shm_toc_insert(pcxt->toc, PARALLEL_KEY_BUFFER_USAGE, bufusage_space);
  	pei->buffer_usage = bufusage_space;
  
  	/* Same for WalUsage. */
  	walusage_space = shm_toc_allocate(pcxt->toc,
  									  mul_size(sizeof(WalUsage), pcxt->nworkers));
  	shm_toc_insert(pcxt->toc, PARALLEL_KEY_WAL_USAGE, walusage_space);
  	pei->wal_usage = walusage_space;
  
  	/* Set up the tuple queues that the workers will write into. */
  	pei->tqueue = ExecParallelSetupTupleQueues(pcxt, false);
  
  	/* We don't need the TupleQueueReaders yet, though. */
  	pei->reader = NULL;
  
  	/*
  	 * If instrumentation options were supplied, allocate space for the data.
  	 * It only gets partially initialized here; the rest happens during
  	 * ExecParallelInitializeDSM.
  	 */
  	if (estate->es_instrument)
  	{
  		Instrumentation *instrument;
  		int			i;
  
  		instrumentation = shm_toc_allocate(pcxt->toc, instrumentation_len);
  		instrumentation->instrument_options = estate->es_instrument;
  		instrumentation->instrument_offset = instrument_offset;
  		instrumentation->num_workers = nworkers;
  		instrumentation->num_plan_nodes = e.nnodes;
  		instrument = GetInstrumentationArray(instrumentation);
  		for (i = 0; i < nworkers * e.nnodes; ++i)
  			InstrInit(&instrument[i], estate->es_instrument);
  		shm_toc_insert(pcxt->toc, PARALLEL_KEY_INSTRUMENTATION,
  					   instrumentation);
  		pei->instrumentation = instrumentation;
  
  		if (estate->es_jit_flags != PGJIT_NONE)
  		{
  			jit_instrumentation = shm_toc_allocate(pcxt->toc,
  												   jit_instrumentation_len);
  			jit_instrumentation->num_workers = nworkers;
  			memset(jit_instrumentation->jit_instr, 0,
  				   sizeof(JitInstrumentation) * nworkers);
  			shm_toc_insert(pcxt->toc, PARALLEL_KEY_JIT_INSTRUMENTATION,
  						   jit_instrumentation);
  			pei->jit_instrumentation = jit_instrumentation;
  		}
  	}
  
  	/*
  	 * Create a DSA area that can be used by the leader and all workers.
  	 * (However, if we failed to create a DSM and are using private memory
  	 * instead, then skip this.)
  	 */
  	if (pcxt->seg != NULL)
  	{
  		char	   *area_space;
  
  		area_space = shm_toc_allocate(pcxt->toc, dsa_minsize);
  		shm_toc_insert(pcxt->toc, PARALLEL_KEY_DSA, area_space);
  		pei->area = dsa_create_in_place(area_space, dsa_minsize,
  										LWTRANCHE_PARALLEL_QUERY_DSA,
  										pcxt->seg);
  
  		/*
  		 * Serialize parameters, if any, using DSA storage.  We don't dare use
  		 * the main parallel query DSM for this because we might relaunch
  		 * workers after the values have changed (and thus the amount of
  		 * storage required has changed).
  		 */
  		if (!bms_is_empty(sendParams))
  		{
  			pei->param_exec = SerializeParamExecParams(estate, sendParams,
  													   pei->area);
  			fpes->param_exec = pei->param_exec;
  		}
  	}
  
  	/*
  	 * Give parallel-aware nodes a chance to initialize their shared data.
  	 * This also initializes the elements of instrumentation->ps_instrument,
  	 * if it exists.
  	 */
  	d.pcxt = pcxt;
  	d.instrumentation = instrumentation;
  	d.nnodes = 0;
  
  	/* Install our DSA area while initializing the plan. */
  	estate->es_query_dsa = pei->area;
  	ExecParallelInitializeDSM(planstate, &d);
  	estate->es_query_dsa = NULL;
  
  	/*
  	 * Make sure that the world hasn't shifted under our feet.  This could
  	 * probably just be an Assert(), but let's be conservative for now.
  	 */
  	if (e.nnodes != d.nnodes)
  		elog(ERROR, "inconsistent count of PlanState nodes");
  
  	/* OK, we're ready to rock and roll. */
  	return pei;
  }
  
  /*
   * Set up tuple queue readers to read the results of a parallel subplan.
   *
   * This is separate from ExecInitParallelPlan() because we can launch the
   * worker processes and let them start doing something before we do this.
   */
  void
  ExecParallelCreateReaders(ParallelExecutorInfo *pei)
  {
  	int			nworkers = pei->pcxt->nworkers_launched;
  	int			i;
  
  	Assert(pei->reader == NULL);
  
  	if (nworkers > 0)
  	{
  		pei->reader = (TupleQueueReader **)
  			palloc(nworkers * sizeof(TupleQueueReader *));
  
  		for (i = 0; i < nworkers; i++)
  		{
  			shm_mq_set_handle(pei->tqueue[i],
  							  pei->pcxt->worker[i].bgwhandle);
  			pei->reader[i] = CreateTupleQueueReader(pei->tqueue[i]);
  		}
  	}
  }
  
  /*
   * Re-initialize the parallel executor shared memory state before launching
   * a fresh batch of workers.
   */
  void
  ExecParallelReinitialize(PlanState *planstate,
  						 ParallelExecutorInfo *pei,
  						 Bitmapset *sendParams)
  {
  	EState	   *estate = planstate->state;
  	FixedParallelExecutorState *fpes;
  
  	/* Old workers must already be shut down */
  	Assert(pei->finished);
  
  	/*
  	 * Force any initplan outputs that we're going to pass to workers to be
  	 * evaluated, if they weren't already (see comments in
  	 * ExecInitParallelPlan).
  	 */
  	ExecSetParamPlanMulti(sendParams, GetPerTupleExprContext(estate));
  
  	ReinitializeParallelDSM(pei->pcxt);
  	pei->tqueue = ExecParallelSetupTupleQueues(pei->pcxt, true);
  	pei->reader = NULL;
  	pei->finished = false;
  
  	fpes = shm_toc_lookup(pei->pcxt->toc, PARALLEL_KEY_EXECUTOR_FIXED, false);
  
  	/* Free any serialized parameters from the last round. */
  	if (DsaPointerIsValid(fpes->param_exec))
  	{
  		dsa_free(pei->area, fpes->param_exec);
  		fpes->param_exec = InvalidDsaPointer;
  	}
  
  	/* Serialize current parameter values if required. */
  	if (!bms_is_empty(sendParams))
  	{
  		pei->param_exec = SerializeParamExecParams(estate, sendParams,
  												   pei->area);
  		fpes->param_exec = pei->param_exec;
  	}
  
  	/* Traverse plan tree and let each child node reset associated state. */
  	estate->es_query_dsa = pei->area;
  	ExecParallelReInitializeDSM(planstate, pei->pcxt);
  	estate->es_query_dsa = NULL;
  }
  
  /*
   * Traverse plan tree to reinitialize per-node dynamic shared memory state
   */
  static bool
  ExecParallelReInitializeDSM(PlanState *planstate,
  							ParallelContext *pcxt)
  {
  	if (planstate == NULL)
  		return false;
  
  	/*
  	 * Call reinitializers for DSM-using plan nodes.
  	 */
  	switch (nodeTag(planstate))
  	{
  		case T_SeqScanState:
  			if (planstate->plan->parallel_aware)
  				ExecSeqScanReInitializeDSM((SeqScanState *) planstate,
  										   pcxt);
  			break;
  		case T_IndexScanState:
  			if (planstate->plan->parallel_aware)
  				ExecIndexScanReInitializeDSM((IndexScanState *) planstate,
  											 pcxt);
  			break;
  		case T_IndexOnlyScanState:
  			if (planstate->plan->parallel_aware)
  				ExecIndexOnlyScanReInitializeDSM((IndexOnlyScanState *) planstate,
  												 pcxt);
  			break;
  		case T_ForeignScanState:
  			if (planstate->plan->parallel_aware)
  				ExecForeignScanReInitializeDSM((ForeignScanState *) planstate,
  											   pcxt);
  			break;
  		case T_AppendState:
  			if (planstate->plan->parallel_aware)
  				ExecAppendReInitializeDSM((AppendState *) planstate, pcxt);
  			break;
  		case T_CustomScanState:
  			if (planstate->plan->parallel_aware)
  				ExecCustomScanReInitializeDSM((CustomScanState *) planstate,
  											  pcxt);
  			break;
  		case T_BitmapHeapScanState:
  			if (planstate->plan->parallel_aware)
  				ExecBitmapHeapReInitializeDSM((BitmapHeapScanState *) planstate,
  											  pcxt);
  			break;
  		case T_HashJoinState:
  			if (planstate->plan->parallel_aware)
  				ExecHashJoinReInitializeDSM((HashJoinState *) planstate,
  											pcxt);
  			break;
  		case T_HashState:
  		case T_SortState:
  			/* these nodes have DSM state, but no reinitialization is required */
  			break;
  
  		default:
  			break;
  	}
  
  	return planstate_tree_walker(planstate, ExecParallelReInitializeDSM, pcxt);
  }
  
  /*
   * Copy instrumentation information about this node and its descendants from
   * dynamic shared memory.
   */
  static bool
  ExecParallelRetrieveInstrumentation(PlanState *planstate,
  									SharedExecutorInstrumentation *instrumentation)
  {
  	Instrumentation *instrument;
  	int			i;
  	int			n;
  	int			ibytes;
  	int			plan_node_id = planstate->plan->plan_node_id;
  	MemoryContext oldcontext;
  
  	/* Find the instrumentation for this node. */
  	for (i = 0; i < instrumentation->num_plan_nodes; ++i)
  		if (instrumentation->plan_node_id[i] == plan_node_id)
  			break;
  	if (i >= instrumentation->num_plan_nodes)
  		elog(ERROR, "plan node %d not found", plan_node_id);
  
  	/* Accumulate the statistics from all workers. */
  	instrument = GetInstrumentationArray(instrumentation);
  	instrument += i * instrumentation->num_workers;
  	for (n = 0; n < instrumentation->num_workers; ++n)
  		InstrAggNode(planstate->instrument, &instrument[n]);
  
  	/*
  	 * Also store the per-worker detail.
  	 *
  	 * Worker instrumentation should be allocated in the same context as the
  	 * regular instrumentation information, which is the per-query context.
  	 * Switch into per-query memory context.
  	 */
  	oldcontext = MemoryContextSwitchTo(planstate->state->es_query_cxt);
  	ibytes = mul_size(instrumentation->num_workers, sizeof(Instrumentation));
  	planstate->worker_instrument =
  		palloc(ibytes + offsetof(WorkerInstrumentation, instrument));
  	MemoryContextSwitchTo(oldcontext);
  
  	planstate->worker_instrument->num_workers = instrumentation->num_workers;
  	memcpy(&planstate->worker_instrument->instrument, instrument, ibytes);
  
  	/* Perform any node-type-specific work that needs to be done. */
  	switch (nodeTag(planstate))
  	{
  		case T_SortState:
  			ExecSortRetrieveInstrumentation((SortState *) planstate);
  			break;
  		case T_HashState:
  			ExecHashRetrieveInstrumentation((HashState *) planstate);
  			break;
  		default:
  			break;
  	}
  
  	return planstate_tree_walker(planstate, ExecParallelRetrieveInstrumentation,
  								 instrumentation);
  }
  
  /*
   * Add up the workers' JIT instrumentation from dynamic shared memory.
   */
  static void
  ExecParallelRetrieveJitInstrumentation(PlanState *planstate,
  									   SharedJitInstrumentation *shared_jit)
  {
  	JitInstrumentation *combined;
  	int			ibytes;
  
  	int			n;
  
  	/*
  	 * Accumulate worker JIT instrumentation into the combined JIT
  	 * instrumentation, allocating it if required.
  	 */
  	if (!planstate->state->es_jit_worker_instr)
  		planstate->state->es_jit_worker_instr =
  			MemoryContextAllocZero(planstate->state->es_query_cxt, sizeof(JitInstrumentation));
  	combined = planstate->state->es_jit_worker_instr;
  
  	/* Accumulate all the workers' instrumentations. */
  	for (n = 0; n < shared_jit->num_workers; ++n)
  		InstrJitAgg(combined, &shared_jit->jit_instr[n]);
  
  	/*
  	 * Store the per-worker detail.
  	 *
  	 * Similar to ExecParallelRetrieveInstrumentation(), allocate the
  	 * instrumentation in per-query context.
  	 */
  	ibytes = offsetof(SharedJitInstrumentation, jit_instr)
  		+ mul_size(shared_jit->num_workers, sizeof(JitInstrumentation));
  	planstate->worker_jit_instrument =
  		MemoryContextAlloc(planstate->state->es_query_cxt, ibytes);
  
  	memcpy(planstate->worker_jit_instrument, shared_jit, ibytes);
  }
  
  /*
   * Finish parallel execution.  We wait for parallel workers to finish, and
   * accumulate their buffer/WAL usage.
   */
  void
  ExecParallelFinish(ParallelExecutorInfo *pei)
  {
  	int			nworkers = pei->pcxt->nworkers_launched;
  	int			i;
  
  	/* Make this be a no-op if called twice in a row. */
  	if (pei->finished)
  		return;
  
  	/*
  	 * Detach from tuple queues ASAP, so that any still-active workers will
  	 * notice that no further results are wanted.
  	 */
  	if (pei->tqueue != NULL)
  	{
  		for (i = 0; i < nworkers; i++)
  			shm_mq_detach(pei->tqueue[i]);
  		pfree(pei->tqueue);
  		pei->tqueue = NULL;
  	}
  
  	/*
  	 * While we're waiting for the workers to finish, let's get rid of the
  	 * tuple queue readers.  (Any other local cleanup could be done here too.)
  	 */
  	if (pei->reader != NULL)
  	{
  		for (i = 0; i < nworkers; i++)
  			DestroyTupleQueueReader(pei->reader[i]);
  		pfree(pei->reader);
  		pei->reader = NULL;
  	}
  
  	/* Now wait for the workers to finish. */
  	WaitForParallelWorkersToFinish(pei->pcxt);
  
  	/*
  	 * Next, accumulate buffer/WAL usage.  (This must wait for the workers to
  	 * finish, or we might get incomplete data.)
  	 */
  	for (i = 0; i < nworkers; i++)
  		InstrAccumParallelQuery(&pei->buffer_usage[i], &pei->wal_usage[i]);
  
  	pei->finished = true;
  }
  
  /*
   * Accumulate instrumentation, and then clean up whatever ParallelExecutorInfo
   * resources still exist after ExecParallelFinish.  We separate these
   * routines because someone might want to examine the contents of the DSM
   * after ExecParallelFinish and before calling this routine.
   */
  void
  ExecParallelCleanup(ParallelExecutorInfo *pei)
  {
  	/* Accumulate instrumentation, if any. */
  	if (pei->instrumentation)
  		ExecParallelRetrieveInstrumentation(pei->planstate,
  											pei->instrumentation);
  
  	/* Accumulate JIT instrumentation, if any. */
  	if (pei->jit_instrumentation)
  		ExecParallelRetrieveJitInstrumentation(pei->planstate,
  											   pei->jit_instrumentation);
  
  	/* Free any serialized parameters. */
  	if (DsaPointerIsValid(pei->param_exec))
  	{
  		dsa_free(pei->area, pei->param_exec);
  		pei->param_exec = InvalidDsaPointer;
  	}
  	if (pei->area != NULL)
  	{
  		dsa_detach(pei->area);
  		pei->area = NULL;
  	}
  	if (pei->pcxt != NULL)
  	{
  		DestroyParallelContext(pei->pcxt);
  		pei->pcxt = NULL;
  	}
  	pfree(pei);
  }
  
  /*
   * Create a DestReceiver to write tuples we produce to the shm_mq designated
   * for that purpose.
   */
  static DestReceiver *
  ExecParallelGetReceiver(dsm_segment *seg, shm_toc *toc)
  {
  	char	   *mqspace;
  	shm_mq	   *mq;
  
  	mqspace = shm_toc_lookup(toc, PARALLEL_KEY_TUPLE_QUEUE, false);
  	mqspace += ParallelWorkerNumber * PARALLEL_TUPLE_QUEUE_SIZE;
  	mq = (shm_mq *) mqspace;
  	shm_mq_set_sender(mq, MyProc);
  	return CreateTupleQueueDestReceiver(shm_mq_attach(mq, seg, NULL));
  }
  
  /*
   * Create a QueryDesc for the PlannedStmt we are to execute, and return it.
   */
  static QueryDesc *
  ExecParallelGetQueryDesc(shm_toc *toc, DestReceiver *receiver,
  						 int instrument_options)
  {
  	char	   *pstmtspace;
  	char	   *paramspace;
  	PlannedStmt *pstmt;
  	ParamListInfo paramLI;
  	char	   *queryString;
  
  	/* Get the query string from shared memory */
  	queryString = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT, false);
  
  	/* Reconstruct leader-supplied PlannedStmt. */
  	pstmtspace = shm_toc_lookup(toc, PARALLEL_KEY_PLANNEDSTMT, false);
  	pstmt = (PlannedStmt *) stringToNode(pstmtspace);
  
  	/* Reconstruct ParamListInfo. */
  	paramspace = shm_toc_lookup(toc, PARALLEL_KEY_PARAMLISTINFO, false);
  	paramLI = RestoreParamList(&paramspace);
  
  	/* Create a QueryDesc for the query. */
  	return CreateQueryDesc(pstmt,
  						   queryString,
  						   GetActiveSnapshot(), InvalidSnapshot,
  						   receiver, paramLI, NULL, instrument_options);
  }
  
  /*
   * Copy instrumentation information from this node and its descendants into
   * dynamic shared memory, so that the parallel leader can retrieve it.
   */
  static bool
  ExecParallelReportInstrumentation(PlanState *planstate,
  								  SharedExecutorInstrumentation *instrumentation)
  {
  	int			i;
  	int			plan_node_id = planstate->plan->plan_node_id;
  	Instrumentation *instrument;
  
  	InstrEndLoop(planstate->instrument);
  
  	/*
  	 * If we shuffled the plan_node_id values in ps_instrument into sorted
  	 * order, we could use binary search here.  This might matter someday if
  	 * we're pushing down sufficiently large plan trees.  For now, do it the
  	 * slow, dumb way.
  	 */
  	for (i = 0; i < instrumentation->num_plan_nodes; ++i)
  		if (instrumentation->plan_node_id[i] == plan_node_id)
  			break;
  	if (i >= instrumentation->num_plan_nodes)
  		elog(ERROR, "plan node %d not found", plan_node_id);
  
  	/*
  	 * Add our statistics to the per-node, per-worker totals.  It's possible
  	 * that this could happen more than once if we relaunched workers.
  	 */
  	instrument = GetInstrumentationArray(instrumentation);
  	instrument += i * instrumentation->num_workers;
  	Assert(IsParallelWorker());
  	Assert(ParallelWorkerNumber < instrumentation->num_workers);
  	InstrAggNode(&instrument[ParallelWorkerNumber], planstate->instrument);
  
  	return planstate_tree_walker(planstate, ExecParallelReportInstrumentation,
  								 instrumentation);
  }
  
  /*
   * Initialize the PlanState and its descendants with the information
   * retrieved from shared memory.  This has to be done once the PlanState
   * is allocated and initialized by executor; that is, after ExecutorStart().
   */
  static bool
  ExecParallelInitializeWorker(PlanState *planstate, ParallelWorkerContext *pwcxt)
  {
  	if (planstate == NULL)
  		return false;
  
  	switch (nodeTag(planstate))
  	{
  		case T_SeqScanState:
  			if (planstate->plan->parallel_aware)
  				ExecSeqScanInitializeWorker((SeqScanState *) planstate, pwcxt);
  			break;
  		case T_IndexScanState:
  			if (planstate->plan->parallel_aware)
  				ExecIndexScanInitializeWorker((IndexScanState *) planstate,
  											  pwcxt);
  			break;
  		case T_IndexOnlyScanState:
  			if (planstate->plan->parallel_aware)
  				ExecIndexOnlyScanInitializeWorker((IndexOnlyScanState *) planstate,
  												  pwcxt);
  			break;
  		case T_ForeignScanState:
  			if (planstate->plan->parallel_aware)
  				ExecForeignScanInitializeWorker((ForeignScanState *) planstate,
  												pwcxt);
  			break;
  		case T_AppendState:
  			if (planstate->plan->parallel_aware)
  				ExecAppendInitializeWorker((AppendState *) planstate, pwcxt);
  			break;
  		case T_CustomScanState:
  			if (planstate->plan->parallel_aware)
  				ExecCustomScanInitializeWorker((CustomScanState *) planstate,
  											   pwcxt);
  			break;
  		case T_BitmapHeapScanState:
  			if (planstate->plan->parallel_aware)
  				ExecBitmapHeapInitializeWorker((BitmapHeapScanState *) planstate,
  											   pwcxt);
  			break;
  		case T_HashJoinState:
  			if (planstate->plan->parallel_aware)
  				ExecHashJoinInitializeWorker((HashJoinState *) planstate,
  											 pwcxt);
  			break;
  		case T_HashState:
  			/* even when not parallel-aware, for EXPLAIN ANALYZE */
  			ExecHashInitializeWorker((HashState *) planstate, pwcxt);
  			break;
  		case T_SortState:
  			/* even when not parallel-aware, for EXPLAIN ANALYZE */
  			ExecSortInitializeWorker((SortState *) planstate, pwcxt);
  			break;
  
  		default:
  			break;
  	}
  
  	return planstate_tree_walker(planstate, ExecParallelInitializeWorker,
  								 pwcxt);
  }
  
  /*
   * Main entrypoint for parallel query worker processes.
   *
   * We reach this function from ParallelWorkerMain, so the setup necessary to
   * create a sensible parallel environment has already been done;
   * ParallelWorkerMain worries about stuff like the transaction state, combo
   * CID mappings, and GUC values, so we don't need to deal with any of that
   * here.
   *
   * Our job is to deal with concerns specific to the executor.  The parallel
   * group leader will have stored a serialized PlannedStmt, and it's our job
   * to execute that plan and write the resulting tuples to the appropriate
   * tuple queue.  Various bits of supporting information that we need in order
   * to do this are also stored in the dsm_segment and can be accessed through
   * the shm_toc.
   */
  void
  ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
  {
  	FixedParallelExecutorState *fpes;
  	BufferUsage *buffer_usage;
  	WalUsage   *wal_usage;
  	DestReceiver *receiver;
  	QueryDesc  *queryDesc;
  	SharedExecutorInstrumentation *instrumentation;
  	SharedJitInstrumentation *jit_instrumentation;
  	int			instrument_options = 0;
  	void	   *area_space;
  	dsa_area   *area;
  	ParallelWorkerContext pwcxt;
  
  	/* Get fixed-size state. */
  	fpes = shm_toc_lookup(toc, PARALLEL_KEY_EXECUTOR_FIXED, false);
  
  	/* Set up DestReceiver, SharedExecutorInstrumentation, and QueryDesc. */
  	receiver = ExecParallelGetReceiver(seg, toc);
  	instrumentation = shm_toc_lookup(toc, PARALLEL_KEY_INSTRUMENTATION, true);
  	if (instrumentation != NULL)
  		instrument_options = instrumentation->instrument_options;
  	jit_instrumentation = shm_toc_lookup(toc, PARALLEL_KEY_JIT_INSTRUMENTATION,
  										 true);
  	queryDesc = ExecParallelGetQueryDesc(toc, receiver, instrument_options);
  
  	/* Setting debug_query_string for individual workers */
  	debug_query_string = queryDesc->sourceText;
  
  	/* Report workers' query for monitoring purposes */
  	pgstat_report_activity(STATE_RUNNING, debug_query_string);
  
  	/* Attach to the dynamic shared memory area. */
  	area_space = shm_toc_lookup(toc, PARALLEL_KEY_DSA, false);
  	area = dsa_attach_in_place(area_space, seg);
  
  	/* Start up the executor */
  	queryDesc->plannedstmt->jitFlags = fpes->jit_flags;
  	ExecutorStart(queryDesc, fpes->eflags);
  
  	/* Special executor initialization steps for parallel workers */
  	queryDesc->planstate->state->es_query_dsa = area;
  	if (DsaPointerIsValid(fpes->param_exec))
  	{
  		char	   *paramexec_space;
  
  		paramexec_space = dsa_get_address(area, fpes->param_exec);
  		RestoreParamExecParams(paramexec_space, queryDesc->estate);
  
  	}
  	pwcxt.toc = toc;
  	pwcxt.seg = seg;
  	ExecParallelInitializeWorker(queryDesc->planstate, &pwcxt);
  
  	/* Pass down any tuple bound */
  	ExecSetTupleBound(fpes->tuples_needed, queryDesc->planstate);
  
  	/*
  	 * Prepare to track buffer/WAL usage during query execution.
  	 *
  	 * We do this after starting up the executor to match what happens in the
  	 * leader, which also doesn't count buffer accesses and WAL activity that
  	 * occur during executor startup.
  	 */
  	InstrStartParallelQuery();
  
  	/*
  	 * Run the plan.  If we specified a tuple bound, be careful not to demand
  	 * more tuples than that.
  	 */
  	ExecutorRun(queryDesc,
  				ForwardScanDirection,
  				fpes->tuples_needed < 0 ? (int64) 0 : fpes->tuples_needed,
  				true);
  
  	/* Shut down the executor */
  	ExecutorFinish(queryDesc);
  
  	/* Report buffer/WAL usage during parallel execution. */
  	buffer_usage = shm_toc_lookup(toc, PARALLEL_KEY_BUFFER_USAGE, false);
  	wal_usage = shm_toc_lookup(toc, PARALLEL_KEY_WAL_USAGE, false);
  	InstrEndParallelQuery(&buffer_usage[ParallelWorkerNumber],
  						  &wal_usage[ParallelWorkerNumber]);
  
  	/* Report instrumentation data if any instrumentation options are set. */
  	if (instrumentation != NULL)
  		ExecParallelReportInstrumentation(queryDesc->planstate,
  										  instrumentation);
  
  	/* Report JIT instrumentation data if any */
  	if (queryDesc->estate->es_jit && jit_instrumentation != NULL)
  	{
  		Assert(ParallelWorkerNumber < jit_instrumentation->num_workers);
  		jit_instrumentation->jit_instr[ParallelWorkerNumber] =
  			queryDesc->estate->es_jit->instr;
  	}
  
  	/* Must do this after capturing instrumentation. */
  	ExecutorEnd(queryDesc);
  
  	/* Cleanup. */
  	dsa_detach(area);
  	FreeQueryDesc(queryDesc);
  	receiver->rDestroy(receiver);
  }
  