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>

9 files changed, 181 insertions, 36 deletions

diff --git a/roomserver/internal/helpers/helpers.go b/roomserver/internal/helpers/helpers.go
index a6de8ac8..7efad7af 100644
--- a/roomserver/internal/helpers/helpers.go
+++ b/roomserver/internal/helpers/helpers.go
@@ -5,6 +5,7 @@ import (
 	"database/sql"
 	"errors"
 	"fmt"
+	"sort"
 	"strings"
 
 	"github.com/matrix-org/gomatrixserverlib"
@@ -159,7 +160,7 @@ func GetMembershipsAtState(
 	ctx context.Context, db storage.Database, stateEntries []types.StateEntry, joinedOnly bool,
 ) ([]types.Event, error) {
 
-	var eventNIDs []types.EventNID
+	var eventNIDs types.EventNIDs
 	for _, entry := range stateEntries {
 		// Filter the events to retrieve to only keep the membership events
 		if entry.EventTypeNID == types.MRoomMemberNID {
@@ -167,6 +168,14 @@ func GetMembershipsAtState(
 		}
 	}
 
+	// There are no events to get, don't bother asking the database
+	if len(eventNIDs) == 0 {
+		return []types.Event{}, nil
+	}
+
+	sort.Sort(eventNIDs)
+	util.Unique(eventNIDs)
+
 	// Get all of the events in this state
 	stateEvents, err := db.Events(ctx, eventNIDs)
 	if err != nil {
diff --git a/roomserver/internal/query/query.go b/roomserver/internal/query/query.go
index 0db046a8..8850e5c4 100644
--- a/roomserver/internal/query/query.go
+++ b/roomserver/internal/query/query.go
@@ -239,16 +239,42 @@ func (r *Queryer) QueryMembershipAtEvent(
 		return fmt.Errorf("unable to get state before event: %w", err)
 	}
 
+	// If we only have one or less state entries, we can short circuit the below
+	// loop and avoid hitting the database
+	allStateEventNIDs := make(map[types.EventNID]types.StateEntry)
+	for _, eventID := range request.EventIDs {
+		stateEntry := stateEntries[eventID]
+		for _, s := range stateEntry {
+			allStateEventNIDs[s.EventNID] = s
+		}
+	}
+
+	var canShortCircuit bool
+	if len(allStateEventNIDs) <= 1 {
+		canShortCircuit = true
+	}
+
+	var memberships []types.Event
 	for _, eventID := range request.EventIDs {
 		stateEntry, ok := stateEntries[eventID]
-		if !ok {
+		if !ok || len(stateEntry) == 0 {
 			response.Memberships[eventID] = []*gomatrixserverlib.HeaderedEvent{}
 			continue
 		}
-		memberships, err := helpers.GetMembershipsAtState(ctx, r.DB, stateEntry, false)
+
+		// If we can short circuit, e.g. we only have 0 or 1 membership events, we only get the memberships
+		// once. If we have more than one membership event, we need to get the state for each state entry.
+		if canShortCircuit {
+			if len(memberships) == 0 {
+				memberships, err = helpers.GetMembershipsAtState(ctx, r.DB, stateEntry, false)
+			}
+		} else {
+			memberships, err = helpers.GetMembershipsAtState(ctx, r.DB, stateEntry, false)
+		}
 		if err != nil {
 			return fmt.Errorf("unable to get memberships at state: %w", err)
 		}
+
 		res := make([]*gomatrixserverlib.HeaderedEvent, 0, len(memberships))
 
 		for i := range memberships {
diff --git a/roomserver/state/state.go b/roomserver/state/state.go
index 01834846..1cfde5e4 100644
--- a/roomserver/state/state.go
+++ b/roomserver/state/state.go
@@ -18,17 +18,17 @@ package state
 
 import (
 	"context"
-	"database/sql"
 	"fmt"
 	"sort"
 	"sync"
 	"time"
 
-	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	"github.com/opentracing/opentracing-go"
 	"github.com/prometheus/client_golang/prometheus"
+
+	"github.com/matrix-org/dendrite/roomserver/types"
 )
 
 type StateResolutionStorage interface {
@@ -37,6 +37,7 @@ type StateResolutionStorage interface {
 	StateBlockNIDs(ctx context.Context, stateNIDs []types.StateSnapshotNID) ([]types.StateBlockNIDList, error)
 	StateEntries(ctx context.Context, stateBlockNIDs []types.StateBlockNID) ([]types.StateEntryList, error)
 	SnapshotNIDFromEventID(ctx context.Context, eventID string) (types.StateSnapshotNID, error)
+	BulkSelectSnapshotsFromEventIDs(ctx context.Context, eventIDs []string) (map[types.StateSnapshotNID][]string, error)
 	StateEntriesForTuples(ctx context.Context, stateBlockNIDs []types.StateBlockNID, stateKeyTuples []types.StateKeyTuple) ([]types.StateEntryList, error)
 	StateAtEventIDs(ctx context.Context, eventIDs []string) ([]types.StateAtEvent, error)
 	AddState(ctx context.Context, roomNID types.RoomNID, stateBlockNIDs []types.StateBlockNID, state []types.StateEntry) (types.StateSnapshotNID, error)
@@ -130,21 +131,10 @@ func (v *StateResolution) LoadMembershipAtEvent(
 	span, ctx := opentracing.StartSpanFromContext(ctx, "StateResolution.LoadMembershipAtEvent")
 	defer span.Finish()
 
-	// De-dupe snapshotNIDs
-	snapshotNIDMap := make(map[types.StateSnapshotNID][]string) // map from snapshot NID to eventIDs
-	for i := range eventIDs {
-		eventID := eventIDs[i]
-		snapshotNID, err := v.db.SnapshotNIDFromEventID(ctx, eventID)
-		if err != nil && err != sql.ErrNoRows {
-			return nil, fmt.Errorf("LoadStateAtEvent.SnapshotNIDFromEventID failed for event %s : %w", eventID, err)
-		}
-		if snapshotNID == 0 {
-			// If we don't know a state snapshot for this event then we can't calculate
-			// memberships at the time of the event, so skip over it. This means that
-			// it isn't guaranteed that the response map will contain every single event.
-			continue
-		}
-		snapshotNIDMap[snapshotNID] = append(snapshotNIDMap[snapshotNID], eventID)
+	// Get a mapping from snapshotNID -> eventIDs
+	snapshotNIDMap, err := v.db.BulkSelectSnapshotsFromEventIDs(ctx, eventIDs)
+	if err != nil {
+		return nil, err
 	}
 
 	snapshotNIDs := make([]types.StateSnapshotNID, 0, len(snapshotNIDMap))
@@ -157,24 +147,45 @@ func (v *StateResolution) LoadMembershipAtEvent(
 		return nil, err
 	}
 
+	var wantStateBlocks []types.StateBlockNID
+	for _, x := range stateBlockNIDLists {
+		wantStateBlocks = append(wantStateBlocks, x.StateBlockNIDs...)
+	}
+
+	stateEntryLists, err := v.db.StateEntriesForTuples(ctx, uniqueStateBlockNIDs(wantStateBlocks), []types.StateKeyTuple{
+		{
+			EventTypeNID:     types.MRoomMemberNID,
+			EventStateKeyNID: stateKeyNID,
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	stateBlockNIDsMap := stateBlockNIDListMap(stateBlockNIDLists)
+	stateEntriesMap := stateEntryListMap(stateEntryLists)
+
 	result := make(map[string][]types.StateEntry)
 	for _, stateBlockNIDList := range stateBlockNIDLists {
-		// Query the membership event for the user at the given stateblocks
-		stateEntryLists, err := v.db.StateEntriesForTuples(ctx, stateBlockNIDList.StateBlockNIDs, []types.StateKeyTuple{
-			{
-				EventTypeNID:     types.MRoomMemberNID,
-				EventStateKeyNID: stateKeyNID,
-			},
-		})
-		if err != nil {
-			return nil, err
+		stateBlockNIDs, ok := stateBlockNIDsMap.lookup(stateBlockNIDList.StateSnapshotNID)
+		if !ok {
+			// This should only get hit if the database is corrupt.
+			// It should be impossible for an event to reference a NID that doesn't exist
+			return nil, fmt.Errorf("corrupt DB: Missing state snapshot numeric ID %d", stateBlockNIDList.StateSnapshotNID)
 		}
 
-		evIDs := snapshotNIDMap[stateBlockNIDList.StateSnapshotNID]
+		for _, stateBlockNID := range stateBlockNIDs {
+			entries, ok := stateEntriesMap.lookup(stateBlockNID)
+			if !ok {
+				// This should only get hit if the database is corrupt.
+				// It should be impossible for an event to reference a NID that doesn't exist
+				return nil, fmt.Errorf("corrupt DB: Missing state block numeric ID %d", stateBlockNID)
+			}
+
+			evIDs := snapshotNIDMap[stateBlockNIDList.StateSnapshotNID]
 
-		for _, evID := range evIDs {
-			for _, x := range stateEntryLists {
-				result[evID] = append(result[evID], x.StateEntries...)
+			for _, evID := range evIDs {
+				result[evID] = append(result[evID], entries...)
 			}
 		}
 	}
diff --git a/roomserver/storage/interface.go b/roomserver/storage/interface.go
index 09453794..c39a8cbb 100644
--- a/roomserver/storage/interface.go
+++ b/roomserver/storage/interface.go
@@ -72,6 +72,7 @@ type Database interface {
 	Events(ctx context.Context, eventNIDs []types.EventNID) ([]types.Event, error)
 	// Look up snapshot NID for an event ID string
 	SnapshotNIDFromEventID(ctx context.Context, eventID string) (types.StateSnapshotNID, error)
+	BulkSelectSnapshotsFromEventIDs(ctx context.Context, eventIDs []string) (map[types.StateSnapshotNID][]string, error)
 	// Stores a matrix room event in the database. Returns the room NID, the state snapshot and the redacted event ID if any, or an error.
 	StoreEvent(
 		ctx context.Context, event *gomatrixserverlib.Event, authEventNIDs []types.EventNID,
diff --git a/roomserver/storage/postgres/events_table.go b/roomserver/storage/postgres/events_table.go
index 1e7ca766..9b5ed6ed 100644
--- a/roomserver/storage/postgres/events_table.go
+++ b/roomserver/storage/postgres/events_table.go
@@ -22,11 +22,12 @@ import (
 	"sort"
 
 	"github.com/lib/pq"
+	"github.com/matrix-org/gomatrixserverlib"
+
 	"github.com/matrix-org/dendrite/internal"
 	"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"
 )
 
 const eventsSchema = `
@@ -80,6 +81,9 @@ const insertEventSQL = "" +
 const selectEventSQL = "" +
 	"SELECT event_nid, state_snapshot_nid FROM roomserver_events WHERE event_id = $1"
 
+const bulkSelectSnapshotsForEventIDsSQL = "" +
+	"SELECT event_id, state_snapshot_nid FROM roomserver_events WHERE event_id = ANY($1)"
+
 // Bulk lookup of events by string ID.
 // Sort by the numeric IDs for event type and state key.
 // This means we can use binary search to lookup entries by type and state key.
@@ -150,6 +154,7 @@ const selectEventRejectedSQL = "" +
 type eventStatements struct {
 	insertEventStmt                               *sql.Stmt
 	selectEventStmt                               *sql.Stmt
+	bulkSelectSnapshotsForEventIDsStmt            *sql.Stmt
 	bulkSelectStateEventByIDStmt                  *sql.Stmt
 	bulkSelectStateEventByIDExcludingRejectedStmt *sql.Stmt
 	bulkSelectStateEventByNIDStmt                 *sql.Stmt
@@ -179,6 +184,7 @@ func PrepareEventsTable(db *sql.DB) (tables.Events, error) {
 	return s, sqlutil.StatementList{
 		{&s.insertEventStmt, insertEventSQL},
 		{&s.selectEventStmt, selectEventSQL},
+		{&s.bulkSelectSnapshotsForEventIDsStmt, bulkSelectSnapshotsForEventIDsSQL},
 		{&s.bulkSelectStateEventByIDStmt, bulkSelectStateEventByIDSQL},
 		{&s.bulkSelectStateEventByIDExcludingRejectedStmt, bulkSelectStateEventByIDExcludingRejectedSQL},
 		{&s.bulkSelectStateEventByNIDStmt, bulkSelectStateEventByNIDSQL},
@@ -230,6 +236,29 @@ func (s *eventStatements) SelectEvent(
 	return types.EventNID(eventNID), types.StateSnapshotNID(stateNID), err
 }
 
+func (s *eventStatements) BulkSelectSnapshotsFromEventIDs(
+	ctx context.Context, txn *sql.Tx, eventIDs []string,
+) (map[types.StateSnapshotNID][]string, error) {
+	stmt := sqlutil.TxStmt(txn, s.bulkSelectSnapshotsForEventIDsStmt)
+
+	rows, err := stmt.QueryContext(ctx, pq.Array(eventIDs))
+	if err != nil {
+		return nil, err
+	}
+
+	var eventID string
+	var stateNID types.StateSnapshotNID
+	result := make(map[types.StateSnapshotNID][]string)
+	for rows.Next() {
+		if err := rows.Scan(&eventID, &stateNID); err != nil {
+			return nil, err
+		}
+		result[stateNID] = append(result[stateNID], eventID)
+	}
+
+	return result, rows.Err()
+}
+
 // bulkSelectStateEventByID lookups a list of state events by event ID.
 // If not excluding rejected events, and any of the requested events are missing from
 // the database it returns a types.MissingEventError. If excluding rejected events,
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,
diff --git a/roomserver/storage/sqlite3/events_table.go b/roomserver/storage/sqlite3/events_table.go
index 950d03b0..f39b9902 100644
--- a/roomserver/storage/sqlite3/events_table.go
+++ b/roomserver/storage/sqlite3/events_table.go
@@ -23,11 +23,12 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/matrix-org/gomatrixserverlib"
+
 	"github.com/matrix-org/dendrite/internal"
 	"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"
 )
 
 const eventsSchema = `
@@ -57,6 +58,9 @@ const insertEventSQL = `
 const selectEventSQL = "" +
 	"SELECT event_nid, state_snapshot_nid FROM roomserver_events WHERE event_id = $1"
 
+const bulkSelectSnapshotsForEventIDsSQL = "" +
+	"SELECT event_id, state_snapshot_nid FROM roomserver_events WHERE event_id IN ($1)"
+
 // Bulk lookup of events by string ID.
 // Sort by the numeric IDs for event type and state key.
 // This means we can use binary search to lookup entries by type and state key.
@@ -124,6 +128,7 @@ type eventStatements struct {
 	db                                            *sql.DB
 	insertEventStmt                               *sql.Stmt
 	selectEventStmt                               *sql.Stmt
+	bulkSelectSnapshotsForEventIDsStmt            *sql.Stmt
 	bulkSelectStateEventByIDStmt                  *sql.Stmt
 	bulkSelectStateEventByIDExcludingRejectedStmt *sql.Stmt
 	bulkSelectStateAtEventByIDStmt                *sql.Stmt
@@ -153,6 +158,7 @@ func PrepareEventsTable(db *sql.DB) (tables.Events, error) {
 	return s, sqlutil.StatementList{
 		{&s.insertEventStmt, insertEventSQL},
 		{&s.selectEventStmt, selectEventSQL},
+		{&s.bulkSelectSnapshotsForEventIDsStmt, bulkSelectSnapshotsForEventIDsSQL},
 		{&s.bulkSelectStateEventByIDStmt, bulkSelectStateEventByIDSQL},
 		{&s.bulkSelectStateEventByIDExcludingRejectedStmt, bulkSelectStateEventByIDExcludingRejectedSQL},
 		{&s.bulkSelectStateAtEventByIDStmt, bulkSelectStateAtEventByIDSQL},
@@ -203,6 +209,40 @@ func (s *eventStatements) SelectEvent(
 	return types.EventNID(eventNID), types.StateSnapshotNID(stateNID), err
 }
 
+func (s *eventStatements) BulkSelectSnapshotsFromEventIDs(
+	ctx context.Context, txn *sql.Tx, eventIDs []string,
+) (map[types.StateSnapshotNID][]string, error) {
+	qry := strings.Replace(bulkSelectSnapshotsForEventIDsSQL, "($1)", sqlutil.QueryVariadic(len(eventIDs)), 1)
+	stmt, err := s.db.Prepare(qry)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, stmt, "BulkSelectSnapshotsFromEventIDs: stmt.close() failed")
+
+	params := make([]interface{}, len(eventIDs))
+	for i := range eventIDs {
+		params[i] = eventIDs[i]
+	}
+
+	rows, err := stmt.QueryContext(ctx, params...)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "BulkSelectSnapshotsFromEventIDs: rows.close() failed")
+
+	var eventID string
+	var stateNID types.StateSnapshotNID
+	result := make(map[types.StateSnapshotNID][]string)
+	for rows.Next() {
+		if err := rows.Scan(&eventID, &stateNID); err != nil {
+			return nil, err
+		}
+		result[stateNID] = append(result[stateNID], eventID)
+	}
+
+	return result, rows.Err()
+}
+
 // bulkSelectStateEventByID lookups a list of state events by event ID.
 // If not excluding rejected events, and any of the requested events are missing from
 // the database it returns a types.MissingEventError. If excluding rejected events,
diff --git a/roomserver/storage/tables/interface.go b/roomserver/storage/tables/interface.go
index 8d6ca324..50d27c75 100644
--- a/roomserver/storage/tables/interface.go
+++ b/roomserver/storage/tables/interface.go
@@ -44,6 +44,7 @@ type Events interface {
 		referenceSHA256 []byte, authEventNIDs []types.EventNID, depth int64, isRejected bool,
 	) (types.EventNID, types.StateSnapshotNID, error)
 	SelectEvent(ctx context.Context, txn *sql.Tx, eventID string) (types.EventNID, types.StateSnapshotNID, error)
+	BulkSelectSnapshotsFromEventIDs(ctx context.Context, txn *sql.Tx, eventIDs []string) (map[types.StateSnapshotNID][]string, error)
 	// bulkSelectStateEventByID lookups a list of state events by event ID.
 	// If any of the requested events are missing from the database it returns a types.MissingEventError
 	BulkSelectStateEventByID(ctx context.Context, txn *sql.Tx, eventIDs []string, excludeRejected bool) ([]types.StateEntry, error)