Optimize history visibility checks (#2848)

This optimizes history visibility checks by (mostly) avoiding database
hits.
Possibly solves https://github.com/matrix-org/dendrite/issues/2777

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

2 files changed, 29 insertions, 1 deletions

diff --git a/roomserver/storage/shared/room_updater.go b/roomserver/storage/shared/room_updater.go
index 42c0c8f2..cc880a6c 100644
--- a/roomserver/storage/shared/room_updater.go
+++ b/roomserver/storage/shared/room_updater.go
@@ -5,8 +5,9 @@ import (
 	"database/sql"
 	"fmt"
 
-	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
+
+	"github.com/matrix-org/dendrite/roomserver/types"
 )
 
 type RoomUpdater struct {
@@ -186,6 +187,10 @@ func (u *RoomUpdater) EventIDs(
 	return u.d.EventsTable.BulkSelectEventID(ctx, u.txn, eventNIDs)
 }
 
+func (u *RoomUpdater) BulkSelectSnapshotsFromEventIDs(ctx context.Context, eventIDs []string) (map[types.StateSnapshotNID][]string, error) {
+	return u.d.EventsTable.BulkSelectSnapshotsFromEventIDs(ctx, u.txn, eventIDs)
+}
+
 func (u *RoomUpdater) StateAtEventIDs(
 	ctx context.Context, eventIDs []string,
 ) ([]types.StateAtEvent, error) {
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index ed86280b..4455ec3b 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -469,6 +469,23 @@ func (d *Database) events(
 			eventNIDs = append(eventNIDs, nid)
 		}
 	}
+	// If we don't need to get any events from the database, short circuit now
+	if len(eventNIDs) == 0 {
+		results := make([]types.Event, 0, len(inputEventNIDs))
+		for _, nid := range inputEventNIDs {
+			event, ok := events[nid]
+			if !ok || event == nil {
+				return nil, fmt.Errorf("event %d missing", nid)
+			}
+			results = append(results, types.Event{
+				EventNID: nid,
+				Event:    event,
+			})
+		}
+		if !redactionsArePermanent {
+			d.applyRedactions(results)
+		}
+	}
 	eventJSONs, err := d.EventJSONTable.BulkSelectEventJSON(ctx, txn, eventNIDs)
 	if err != nil {
 		return nil, err
@@ -534,6 +551,12 @@ func (d *Database) events(
 	return results, nil
 }
 
+func (d *Database) BulkSelectSnapshotsFromEventIDs(
+	ctx context.Context, eventIDs []string,
+) (map[types.StateSnapshotNID][]string, error) {
+	return d.EventsTable.BulkSelectSnapshotsFromEventIDs(ctx, nil, eventIDs)
+}
+
 func (d *Database) MembershipUpdater(
 	ctx context.Context, roomID, targetUserID string,
 	targetLocal bool, roomVersion gomatrixserverlib.RoomVersion,