`/sync` performance optimizations (#2927)

Since #2849 there is no limit for the current state we fetch to
calculate history visibility. In large rooms this can cause us to fetch
thousands of membership events we don't really care about.
This now only gets the state event types and senders in our timeline,
which should significantly reduce the amount of events we fetch from the
database.

Also removes `MaxTopologicalPosition`, as it is an unnecessary DB call,
given we use the result in `topological_position < $1` calls.

1 files changed, 0 insertions, 19 deletions

diff --git a/syncapi/storage/postgres/output_room_events_topology_table.go b/syncapi/storage/postgres/output_room_events_topology_table.go
index 6fab900e..d0e99f26 100644
--- a/syncapi/storage/postgres/output_room_events_topology_table.go
+++ b/syncapi/storage/postgres/output_room_events_topology_table.go
@@ -65,14 +65,6 @@ const selectPositionInTopologySQL = "" +
 	"SELECT topological_position, stream_position FROM syncapi_output_room_events_topology" +
 	" WHERE event_id = $1"
 
-	// Select the max topological position for the room, then sort by stream position and take the highest,
-	// returning both topological and stream positions.
-const selectMaxPositionInTopologySQL = "" +
-	"SELECT topological_position, stream_position FROM syncapi_output_room_events_topology" +
-	" WHERE topological_position=(" +
-	"SELECT MAX(topological_position) FROM syncapi_output_room_events_topology WHERE room_id=$1" +
-	") ORDER BY stream_position DESC LIMIT 1"
-
 const selectStreamToTopologicalPositionAscSQL = "" +
 	"SELECT topological_position FROM syncapi_output_room_events_topology WHERE room_id = $1 AND stream_position >= $2 ORDER BY topological_position ASC LIMIT 1;"
 
@@ -84,7 +76,6 @@ type outputRoomEventsTopologyStatements struct {
 	selectEventIDsInRangeASCStmt              *sql.Stmt
 	selectEventIDsInRangeDESCStmt             *sql.Stmt
 	selectPositionInTopologyStmt              *sql.Stmt
-	selectMaxPositionInTopologyStmt           *sql.Stmt
 	selectStreamToTopologicalPositionAscStmt  *sql.Stmt
 	selectStreamToTopologicalPositionDescStmt *sql.Stmt
 }
@@ -107,9 +98,6 @@ func NewPostgresTopologyTable(db *sql.DB) (tables.Topology, error) {
 	if s.selectPositionInTopologyStmt, err = db.Prepare(selectPositionInTopologySQL); err != nil {
 		return nil, err
 	}
-	if s.selectMaxPositionInTopologyStmt, err = db.Prepare(selectMaxPositionInTopologySQL); err != nil {
-		return nil, err
-	}
 	if s.selectStreamToTopologicalPositionAscStmt, err = db.Prepare(selectStreamToTopologicalPositionAscSQL); err != nil {
 		return nil, err
 	}
@@ -189,10 +177,3 @@ func (s *outputRoomEventsTopologyStatements) SelectStreamToTopologicalPosition(
 	}
 	return
 }
-
-func (s *outputRoomEventsTopologyStatements) SelectMaxPositionInTopology(
-	ctx context.Context, txn *sql.Tx, roomID string,
-) (pos types.StreamPosition, spos types.StreamPosition, err error) {
-	err = sqlutil.TxStmt(txn, s.selectMaxPositionInTopologyStmt).QueryRowContext(ctx, roomID).Scan(&pos, &spos)
-	return
-}