Implement incremental sync
This has the following known shortcomings:
- It doesn't handle missing events not in the from/to range.
- It doesn't order events in the timeline correctly.
- It doesn't handle invited/left rooms at all.
- There is no intelligent wakeup logic: events for Bob will wake up Alice's stream.
ADD
src/github.com/matrix-org/dendrite/syncserver/README.md
+# Sync Server
+
+This server is responsible for servicing `/sync` requests. It gets its data from the room server output log.
+
+## Internals
+
+When the server gets a `/sync` request, it needs to:
+ - Work out *which* rooms to return to the client.
+ - For each room, work out *which* events to return to the client.
+
+The logic for working out which rooms is based on [Synapse](https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L821):
+ 1) Get the CURRENT joined room list for this user.
+ 2) Get membership list changes for this user between the provided stream position and now.
+ 3) For each room which has membership list changes:
+ - Check if the room is 'newly joined' (insufficient to just check for a join event because we allow dupe joins).
+ If it is, then we need to send the full room state down (and 'limited' is always true).
+ - Check if user is still CURRENTLY invited to the room. If so, add room to 'invited' block.
+ - Check if the user is CURRENTLY left/banned. If so, add room to 'archived' block.
+ 4) Add joined rooms (joined room list)
+
+For each room, the /sync response returns the most recent timeline events and the state of the room at the start of the timeline.
+The logic for working out *which* events is not based entirely on Synapse code, as it is known broken with respect to working out
+room state. In order to know which events to return, the server needs to calculate room state at various points in the history of
+the room. For example, imagine a room with the following 15 events (letters are state events (updated via `'`), numbers are timeline events):
+
+```
+index 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 (1-based indexing as StreamPosition(0) represents no event)
+timeline [A, B, C, D, 1, 2, 3, D', 4, D'', 5, B', D''', D'''', 6]
+```
+
+The current state of this room is: `[A, B', C, D'''']`.
+
+If this room was requested with `?since=14&limit=5` then 1 timeline event would be returned, the most recent one:
+```
+ 15
+ [ 6 ]
+```
+
+If this room was requested with `?since=9&limit=5` then 5 timeline events would be returned, the most recent ones:
+```
+ 11 12 13 14 15
+ [5, B', D''', D'''', 6]
+```
+
+The state of the room at the START of the timeline can be represented in 2 ways:
+ - The `full_state` from index 0 : `[A, B, C, D'']` (aka the state between 0-11 exclusive)
+ - A partial state from index 9 : `[D'']` (aka the state between 9-11 exclusive)
+
+Servers advance state events (e.g from `D'` to `D''`) based on the state conflict resolution algorithm.
+You might think that you could advance the current state by just updating the entry for the `(event type, state_key)` tuple
+for each state event, but this state can diverge from the state calculated using the state conflict resolution algorithm.
+For example, if there are two "simultaneous" updates to the same state key, that is two updates at the same depth in the
+event graph, then the final result of the state conflict resolution algorithm might not match the order the events appear
+in the timeline.
+
+The correct advancement for state events is represented by the `AddsStateEventIDs` and `RemovesStateEventIDs` that
+are in `OutputRoomEvents` from the room server.
+
+This version of the sync server uses very simple indexing to calculate room state at various points.
+This is inefficient when a very old `since` value is provided, or the `full_state` is requested, as the state delta becomes
+very large. This is mitigated slightly with indexes, but better data structures could be used in the future.

MODIFY
src/github.com/matrix-org/dendrite/syncserver/storage/output_room_events_table.go
src/github.com/matrix-org/dendrite/syncserver/storage/output_room_events_table.go
@@ -4,7 +4,9 @@ import (
"database/sql"
"fmt"
+ log "github.com/Sirupsen/logrus"
"github.com/lib/pq"
+ "github.com/matrix-org/dendrite/syncserver/types"
"github.com/matrix-org/gomatrixserverlib"
)
@@ -40,17 +42,24 @@ const selectEventsInRangeSQL = "" +
"SELECT event_json FROM output_room_events WHERE id > $1 AND id <= $2"
const selectRecentEventsSQL = "" +
- "SELECT event_json FROM output_room_events WHERE room_id = $1 ORDER BY id DESC LIMIT $2"
+ "SELECT event_json FROM output_room_events WHERE room_id = $1 AND id > $2 AND id <= $3 ORDER BY id DESC LIMIT $4"
const selectMaxIDSQL = "" +
"SELECT MAX(id) FROM output_room_events"
+// In order for us to apply the state updates correctly, rows need to be ordered in the order they were received (id).
+const selectStateInRangeSQL = "" +
+ "SELECT event_json, add_state_ids, remove_state_ids FROM output_room_events" +
+ " WHERE (id > $1 AND id < $2) AND (add_state_ids IS NOT NULL OR remove_state_ids IS NOT NULL)" +
+ " ORDER BY id ASC"
+
type outputRoomEventsStatements struct {
insertEventStmt *sql.Stmt
selectEventsStmt *sql.Stmt
selectMaxIDStmt *sql.Stmt
selectEventsInRangeStmt *sql.Stmt
selectRecentEventsStmt *sql.Stmt
+ selectStateInRangeStmt *sql.Stmt
}
func (s *outputRoomEventsStatements) prepare(db *sql.DB) (err error) {
@@ -73,9 +82,102 @@ func (s *outputRoomEventsStatements) prepare(db *sql.DB) (err error) {
if s.selectRecentEventsStmt, err = db.Prepare(selectRecentEventsSQL); err != nil {
return
}
+ if s.selectStateInRangeStmt, err = db.Prepare(selectStateInRangeSQL); err != nil {
+ return
+ }
return
}
+// StateBetween returns the state events between the two given stream positions, exclusive of both.
+// Results are bucketed based on the room ID. If the same state is overwritten multiple times between the
+// two positions, only the most recent state is returned.
+func (s *outputRoomEventsStatements) StateBetween(txn *sql.Tx, oldPos, newPos types.StreamPosition) (map[string][]gomatrixserverlib.Event, error) {
+ rows, err := txn.Stmt(s.selectStateInRangeStmt).Query(oldPos, newPos)
+ if err != nil {
+ return nil, err
+ }
+ // Fetch all the state change events for all rooms between the two positions then loop each event and:
+ // - Keep a cache of the event by ID (99% of state change events are for the event itself)
+ // - For each room ID, build up an array of event IDs which represents cumulative adds/removes
+ // For each room, map cumulative event IDs to events and return. This may need to a batch SELECT based on event ID
+ // if they aren't in the event ID cache. We don't handle state deletion yet.
+ eventIDToEvent := make(map[string]gomatrixserverlib.Event)
+
+ // RoomID => A set (map[string]bool) of state event IDs which are between the two positions
+ stateNeeded := make(map[string]map[string]bool)
+
+ for rows.Next() {
+ var (
+ eventBytes []byte
+ addIDs pq.StringArray
+ delIDs pq.StringArray
+ )
+ if err := rows.Scan(&eventBytes, &addIDs, &delIDs); err != nil {
+ return nil, err
+ }
+ // Sanity check for deleted state and whine if we see it. We don't need to do anything
+ // since it'll just mark the event as not being needed.
+ if len(addIDs) < len(delIDs) {
+ log.WithFields(log.Fields{
+ "since": oldPos,
+ "current": newPos,
+ "adds": addIDs,
+ "dels": delIDs,
+ }).Warn("StateBetween: ignoring deleted state")
+ }
+
+ // TODO: Handle redacted events
+ ev, err := gomatrixserverlib.NewEventFromTrustedJSON(eventBytes, false)
+ if err != nil {
+ return nil, err
+ }
+ needSet := stateNeeded[ev.RoomID()]
+ if needSet == nil { // make set if required
+ needSet = make(map[string]bool)
+ }
+ for _, id := range delIDs {
+ needSet[id] = false
+ }
+ for _, id := range addIDs {
+ needSet[id] = true
+ }
+ stateNeeded[ev.RoomID()] = needSet
+
+ eventIDToEvent[ev.EventID()] = ev
+ }
+
+ stateBetween, missingEvents := mapEventIDsToEvents(eventIDToEvent, stateNeeded)
+
+ if len(missingEvents) > 0 {
+ return nil, fmt.Errorf("error StateBetween: TODO missing events")
+ }
+ return stateBetween, nil
+}
+
+// convert the set of event IDs into a set of events. Mark any which are missing.
+func mapEventIDsToEvents(eventIDToEvent map[string]gomatrixserverlib.Event, stateNeeded map[string]map[string]bool) (map[string][]gomatrixserverlib.Event, map[string][]string) {
+ stateBetween := make(map[string][]gomatrixserverlib.Event)
+ missingEvents := make(map[string][]string)
+ for roomID, ids := range stateNeeded {
+ events := stateBetween[roomID]
+ for id, need := range ids {
+ if !need {
+ continue // deleted state
+ }
+ e, ok := eventIDToEvent[id]
+ if ok {
+ events = append(events, e)
+ } else {
+ m := missingEvents[roomID]
+ m = append(m, id)
+ missingEvents[roomID] = m
+ }
+ }
+ stateBetween[roomID] = events
+ }
+ return stateBetween, missingEvents
+}
+
// MaxID returns the ID of the last inserted event in this table. 'txn' is optional. If it is not supplied,
// then this function should only ever be used at startup, as it will race with inserting events if it is
// done afterwards. If there are no inserted events, 0 is returned.
@@ -92,27 +194,6 @@ func (s *outputRoomEventsStatements) MaxID(txn *sql.Tx) (id int64, err error) {
return
}
-// InRange returns all the events in the range between oldPos exclusive and newPos inclusive. Returns an empty array if
-// there are no events between the provided range. Returns an error if events are missing in the range.
-func (s *outputRoomEventsStatements) InRange(oldPos, newPos int64) ([]gomatrixserverlib.Event, error) {
- rows, err := s.selectEventsInRangeStmt.Query(oldPos, newPos)
- if err != nil {
- return nil, err
- }
- defer rows.Close()
-
- result, err := rowsToEvents(rows)
- if err != nil {
- return nil, err
- }
- // Expect one event per position, exclusive of old. eg old=3, new=5, expect 4,5 so 2 events.
- wantNum := int(newPos - oldPos)
- if len(result) != wantNum {
- return nil, fmt.Errorf("failed to map all positions to events: (got %d, wanted, %d)", len(result), wantNum)
- }
- return result, nil
-}
-
// InsertEvent into the output_room_events table. addState and removeState are an optional list of state event IDs. Returns the position
// of the inserted event.
func (s *outputRoomEventsStatements) InsertEvent(txn *sql.Tx, event *gomatrixserverlib.Event, addState, removeState []string) (streamPos int64, err error) {
@@ -123,8 +204,8 @@ func (s *outputRoomEventsStatements) InsertEvent(txn *sql.Tx, event *gomatrixser
}
// RecentEventsInRoom returns the most recent events in the given room, up to a maximum of 'limit'.
-func (s *outputRoomEventsStatements) RecentEventsInRoom(txn *sql.Tx, roomID string, limit int) ([]gomatrixserverlib.Event, error) {
- rows, err := s.selectRecentEventsStmt.Query(roomID, limit)
+func (s *outputRoomEventsStatements) RecentEventsInRoom(txn *sql.Tx, roomID string, fromPos, toPos types.StreamPosition, limit int) ([]gomatrixserverlib.Event, error) {
+ rows, err := s.selectRecentEventsStmt.Query(roomID, fromPos, toPos, limit)
if err != nil {
return nil, err
}

MODIFY
src/github.com/matrix-org/dendrite/syncserver/storage/syncserver.go
src/github.com/matrix-org/dendrite/syncserver/storage/syncserver.go
@@ -96,6 +96,36 @@ func (d *SyncServerDatabase) SyncStreamPosition() (types.StreamPosition, error)
return types.StreamPosition(id), nil
}
+// IncrementalSync returns all the data needed in order to create an incremental sync response.
+func (d *SyncServerDatabase) IncrementalSync(userID string, fromPos, toPos types.StreamPosition, numRecentEventsPerRoom int) (data map[string]types.RoomData, returnErr error) {
+ data = make(map[string]types.RoomData)
+ returnErr = runTransaction(d.db, func(txn *sql.Tx) error {
+ roomIDs, err := d.roomstate.SelectRoomIDsWithMembership(txn, userID, "join")
+ if err != nil {
+ return err
+ }
+
+ state, err := d.events.StateBetween(txn, fromPos, toPos)
+ if err != nil {
+ return err
+ }
+
+ for _, roomID := range roomIDs {
+ recentEvents, err := d.events.RecentEventsInRoom(txn, roomID, fromPos, toPos, numRecentEventsPerRoom)
+ if err != nil {
+ return err
+ }
+ roomData := types.RoomData{
+ State: state[roomID],
+ RecentEvents: recentEvents,
+ }
+ data[roomID] = roomData
+ }
+ return nil
+ })
+ return
+}
+
// CompleteSync returns all the data needed in order to create a complete sync response.
func (d *SyncServerDatabase) CompleteSync(userID string, numRecentEventsPerRoom int) (pos types.StreamPosition, data map[string]types.RoomData, returnErr error) {
data = make(map[string]types.RoomData)
@@ -121,7 +151,7 @@ func (d *SyncServerDatabase) CompleteSync(userID string, numRecentEventsPerRoom
}
// TODO: When filters are added, we may need to call this multiple times to get enough events.
// See: https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L316
- recentEvents, err := d.events.RecentEventsInRoom(txn, roomID, numRecentEventsPerRoom)
+ recentEvents, err := d.events.RecentEventsInRoom(txn, roomID, types.StreamPosition(0), pos, numRecentEventsPerRoom)
if err != nil {
return err
}
@@ -135,11 +165,6 @@ func (d *SyncServerDatabase) CompleteSync(userID string, numRecentEventsPerRoom
return
}
-// EventsInRange returns all events in the given range, exclusive of oldPos, inclusive of newPos.
-func (d *SyncServerDatabase) EventsInRange(oldPos, newPos types.StreamPosition) ([]gomatrixserverlib.Event, error) {
- return d.events.InRange(int64(oldPos), int64(newPos))
-}
-
func runTransaction(db *sql.DB, fn func(txn *sql.Tx) error) (err error) {
txn, err := db.Begin()
if err != nil {

MODIFY
src/github.com/matrix-org/dendrite/syncserver/sync/requestpool.go
src/github.com/matrix-org/dendrite/syncserver/sync/requestpool.go
@@ -139,31 +139,18 @@ func (rp *RequestPool) currentSyncForUser(req syncRequest) (*types.Response, err
// TODO: handle ignored users
- // TODO: Implement https://github.com/matrix-org/synapse/blob/v0.19.3/synapse/handlers/sync.py#L821
- // 1) Get the CURRENT joined room list for this user
- // 2) Get membership list changes for this user between the provided stream position and now.
- // 3) For each room which has membership list changes:
- // a) Check if the room is 'newly joined' (insufficient to just check for a join event because we allow dupe joins).
- // If it is, then we need to send the full room state down (and 'limited' is always true).
- // b) Check if user is still CURRENTLY invited to the room. If so, add room to 'invited' block.
- // c) Check if the user is CURRENTLY left/banned. If so, add room to 'archived' block. // Synapse has a TODO: How do we handle ban -> leave in same batch?
- // 4) Add joined rooms (joined room list)
-
- evs, err := rp.db.EventsInRange(req.since, currentPos)
+ data, err := rp.db.IncrementalSync(req.userID, req.since, currentPos, req.limit)
if err != nil {
return nil, err
}
res := types.NewResponse(currentPos)
- // for now, dump everything as join timeline events
- for _, ev := range evs {
- roomData := res.Rooms.Join[ev.RoomID()]
- roomData.Timeline.Events = append(roomData.Timeline.Events, gomatrixserverlib.ToClientEvent(ev, gomatrixserverlib.FormatSync))
- res.Rooms.Join[ev.RoomID()] = roomData
+ for roomID, d := range data {
+ jr := types.NewJoinResponse()
+ jr.Timeline.Events = gomatrixserverlib.ToClientEvents(d.RecentEvents, gomatrixserverlib.FormatSync)
+ jr.Timeline.Limited = false // TODO: if len(events) >= numRecents + 1 and then set limited:true
+ jr.State.Events = gomatrixserverlib.ToClientEvents(d.State, gomatrixserverlib.FormatSync)
+ res.Rooms.Join[roomID] = *jr
}
-
- // Make sure we send the next_batch as a string. We don't want to confuse clients by sending this
- // as an integer even though (at the moment) it is.
- res.NextBatch = currentPos.String()
return res, nil
}

MODIFY
src/github.com/matrix-org/dendrite/syncserver/types/types.go
src/github.com/matrix-org/dendrite/syncserver/types/types.go
package types
import (
- "github.com/matrix-org/gomatrixserverlib"
"strconv"
+
+ "github.com/matrix-org/gomatrixserverlib"
)
// StreamPosition represents the offset in the sync stream a client is at.
@@ -38,6 +39,8 @@ type Response struct {
// NewResponse creates an empty response with initialised maps.
func NewResponse(pos StreamPosition) *Response {
res := Response{}
+ // Make sure we send the next_batch as a string. We don't want to confuse clients by sending this
+ // as an integer even though (at the moment) it is.
res.NextBatch = pos.String()
// Pre-initalise the maps. Synapse will return {} even if there are no rooms under a specific section,
// so let's do the same thing. Bonus: this means we can't get dreaded 'assignment to entry in nil map' errors.

Implement incremental sync (#71)

This has the following known shortcomings:
 - It doesn't handle missing events not in the from/to range.
 - It doesn't order events in the timeline correctly.
 - It doesn't handle invited/left rooms at all.
 - There is no intelligent wakeup logic: events for Bob will wake up Alice's stream.