Optimize /sync and history visibility (#2961)

Should fix the following issues or make a lot less worse when using
Postgres:

The main issue behind #2911: The client gives up after a certain time,
causing a cascade of context errors, because the response couldn't be
built up fast enough. This mostly happens on accounts with many rooms,
due to the inefficient way we're getting recent events and current state

For #2777: The queries for getting the membership events for history
visibility were being executed for each room (I think 185?), resulting
in a whooping 2k queries for membership events. (Getting the
statesnapshot -> block nids -> actual wanted membership event)

Both should now be better by:
- Using a LATERAL join to get all recent events for all joined rooms in
one go (TODO: maybe do the same for room summary and current state etc)
- If we're lazy loading on initial syncs, we're now not getting the
whole current state, just to drop the majority of it because we're lazy
loading members - we add a filter to exclude membership events on the
first call to `CurrentState`.
- Using an optimized query to get the membership events needed to
calculate history visibility

---------

Co-authored-by: kegsay <kegan@matrix.org>

roomserver/storage/interface.go

@@ -175,4 +175,11 @@ type Database interface {
 	GetLeftUsers(ctx context.Context, userIDs []string) ([]string, error)
 	PurgeRoom(ctx context.Context, roomID string) error
 	UpgradeRoom(ctx context.Context, oldRoomID, newRoomID, eventSender string) error
+
+	// GetMembershipForHistoryVisibility queries the membership events for the given eventIDs.
+	// Returns a map from (input) eventID -> membership event. If no membership event is found, returns an empty event, resulting in
+	// a membership of "leave" when calculating history visibility.
+	GetMembershipForHistoryVisibility(
+		ctx context.Context, userNID types.EventStateKeyNID, info *types.RoomInfo, eventIDs ...string,
+	) (map[string]*gomatrixserverlib.HeaderedEvent, error)
 }

roomserver/storage/postgres/events_table.go

@@ -69,6 +69,9 @@ CREATE TABLE IF NOT EXISTS roomserver_events (
 	auth_event_nids BIGINT[] NOT NULL,
 	is_rejected BOOLEAN NOT NULL DEFAULT FALSE
 );
+
+-- Create an index which helps in resolving membership events (event_type_nid = 5) - (used for history visibility)
+CREATE INDEX IF NOT EXISTS roomserver_events_memberships_idx ON roomserver_events (room_nid, event_state_key_nid) WHERE (event_type_nid = 5);
 `
 
 const insertEventSQL = "" +

roomserver/storage/postgres/state_snapshot_table.go

@@ -21,10 +21,10 @@ import (
 	"fmt"
 
 	"github.com/lib/pq"
+	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 
 	"github.com/matrix-org/dendrite/internal/sqlutil"
-	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 	"github.com/matrix-org/dendrite/roomserver/types"
 )
 
@@ -99,10 +99,26 @@ const bulkSelectStateForHistoryVisibilitySQL = `
 	  AND (event_type_nid = 7 OR event_state_key LIKE '%:' || $2);
 `
 
+// bulkSelectMembershipForHistoryVisibilitySQL is an optimization to get membership events for a specific user for defined set of events.
+// Returns the event_id of the event we want the membership event for, the event_id of the membership event and the membership event JSON.
+const bulkSelectMembershipForHistoryVisibilitySQL = `
+SELECT re.event_id, re2.event_id, rej.event_json
+FROM roomserver_events re
+LEFT JOIN roomserver_state_snapshots rss on re.state_snapshot_nid = rss.state_snapshot_nid
+CROSS JOIN unnest(rss.state_block_nids) AS blocks(block_nid)
+LEFT JOIN roomserver_state_block rsb ON rsb.state_block_nid = blocks.block_nid
+CROSS JOIN unnest(rsb.event_nids) AS rsb2(event_nid)
+JOIN roomserver_events re2 ON re2.room_nid = $3 AND re2.event_type_nid = 5 AND re2.event_nid = rsb2.event_nid AND re2.event_state_key_nid = $1
+LEFT JOIN roomserver_event_json rej ON rej.event_nid = re2.event_nid
+WHERE re.event_id = ANY($2)
+
+`
+
 type stateSnapshotStatements struct {
-	insertStateStmt                         *sql.Stmt
-	bulkSelectStateBlockNIDsStmt            *sql.Stmt
-	bulkSelectStateForHistoryVisibilityStmt *sql.Stmt
+	insertStateStmt                               *sql.Stmt
+	bulkSelectStateBlockNIDsStmt                  *sql.Stmt
+	bulkSelectStateForHistoryVisibilityStmt       *sql.Stmt
+	bulktSelectMembershipForHistoryVisibilityStmt *sql.Stmt
 }
 
 func CreateStateSnapshotTable(db *sql.DB) error {
@@ -110,13 +126,14 @@ func CreateStateSnapshotTable(db *sql.DB) error {
 	return err
 }
 
-func PrepareStateSnapshotTable(db *sql.DB) (tables.StateSnapshot, error) {
+func PrepareStateSnapshotTable(db *sql.DB) (*stateSnapshotStatements, error) {
 	s := &stateSnapshotStatements{}
 
 	return s, sqlutil.StatementList{
 		{&s.insertStateStmt, insertStateSQL},
 		{&s.bulkSelectStateBlockNIDsStmt, bulkSelectStateBlockNIDsSQL},
 		{&s.bulkSelectStateForHistoryVisibilityStmt, bulkSelectStateForHistoryVisibilitySQL},
+		{&s.bulktSelectMembershipForHistoryVisibilityStmt, bulkSelectMembershipForHistoryVisibilitySQL},
 	}.Prepare(db)
 }
 
@@ -185,3 +202,45 @@ func (s *stateSnapshotStatements) BulkSelectStateForHistoryVisibility(
 	}
 	return results, rows.Err()
 }
+
+func (s *stateSnapshotStatements) BulkSelectMembershipForHistoryVisibility(
+	ctx context.Context, txn *sql.Tx, userNID types.EventStateKeyNID, roomInfo *types.RoomInfo, eventIDs ...string,
+) (map[string]*gomatrixserverlib.HeaderedEvent, error) {
+	stmt := sqlutil.TxStmt(txn, s.bulktSelectMembershipForHistoryVisibilityStmt)
+	rows, err := stmt.QueryContext(ctx, userNID, pq.Array(eventIDs), roomInfo.RoomNID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close() // nolint: errcheck
+	result := make(map[string]*gomatrixserverlib.HeaderedEvent, len(eventIDs))
+	var evJson []byte
+	var eventID string
+	var membershipEventID string
+
+	knownEvents := make(map[string]*gomatrixserverlib.HeaderedEvent, len(eventIDs))
+
+	for rows.Next() {
+		if err = rows.Scan(&eventID, &membershipEventID, &evJson); err != nil {
+			return nil, err
+		}
+		if len(evJson) == 0 {
+			result[eventID] = &gomatrixserverlib.HeaderedEvent{}
+			continue
+		}
+		// If we already know this event, don't try to marshal the json again
+		if ev, ok := knownEvents[membershipEventID]; ok {
+			result[eventID] = ev
+			continue
+		}
+		event, err := gomatrixserverlib.NewEventFromTrustedJSON(evJson, false, roomInfo.RoomVersion)
+		if err != nil {
+			result[eventID] = &gomatrixserverlib.HeaderedEvent{}
+			// not fatal
+			continue
+		}
+		he := event.Headered(roomInfo.RoomVersion)
+		result[eventID] = he
+		knownEvents[membershipEventID] = he
+	}
+	return result, rows.Err()
+}

roomserver/storage/shared/storage.go

@@ -51,6 +51,12 @@ func (d *Database) SupportsConcurrentRoomInputs() bool {
 	return true
 }
 
+func (d *Database) GetMembershipForHistoryVisibility(
+	ctx context.Context, userNID types.EventStateKeyNID, roomInfo *types.RoomInfo, eventIDs ...string,
+) (map[string]*gomatrixserverlib.HeaderedEvent, error) {
+	return d.StateSnapshotTable.BulkSelectMembershipForHistoryVisibility(ctx, nil, userNID, roomInfo, eventIDs...)
+}
+
 func (d *Database) EventTypeNIDs(
 	ctx context.Context, eventTypes []string,
 ) (map[string]types.EventTypeNID, error) {

roomserver/storage/sqlite3/state_snapshot_table.go

@@ -26,6 +26,7 @@ import (
 	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 	"github.com/matrix-org/dendrite/roomserver/types"
+	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 )
 
@@ -152,6 +153,10 @@ func (s *stateSnapshotStatements) BulkSelectStateForHistoryVisibility(
 	return nil, tables.OptimisationNotSupportedError
 }
 
+func (s *stateSnapshotStatements) BulkSelectMembershipForHistoryVisibility(ctx context.Context, txn *sql.Tx, userNID types.EventStateKeyNID, roomInfo *types.RoomInfo, eventIDs ...string) (map[string]*gomatrixserverlib.HeaderedEvent, error) {
+	return nil, tables.OptimisationNotSupportedError
+}
+
 func (s *stateSnapshotStatements) selectStateBlockNIDsForRoomNID(
 	ctx context.Context, txn *sql.Tx, roomNID types.RoomNID,
 ) ([]types.StateBlockNID, error) {

roomserver/storage/tables/interface.go

@@ -91,6 +91,10 @@ type StateSnapshot interface {
 	// which users are in a room faster than having to load the entire room state. In the
 	// case of SQLite, this will return tables.OptimisationNotSupportedError.
 	BulkSelectStateForHistoryVisibility(ctx context.Context, txn *sql.Tx, stateSnapshotNID types.StateSnapshotNID, domain string) ([]types.EventNID, error)
+
+	BulkSelectMembershipForHistoryVisibility(
+		ctx context.Context, txn *sql.Tx, userNID types.EventStateKeyNID, roomInfo *types.RoomInfo, eventIDs ...string,
+	) (map[string]*gomatrixserverlib.HeaderedEvent, error)
 }
 
 type StateBlock interface {

roomserver/storage/tables/state_snapshot_table_test.go

@@ -29,6 +29,8 @@ func mustCreateStateSnapshotTable(t *testing.T, dbType test.DBType) (tab tables.
 		assert.NoError(t, err)
 		err = postgres.CreateEventsTable(db)
 		assert.NoError(t, err)
+		err = postgres.CreateEventJSONTable(db)
+		assert.NoError(t, err)
 		err = postgres.CreateStateBlockTable(db)
 		assert.NoError(t, err)
 		// ... and then the snapshot table itself