Not supported on SQLite

roomserver/internal/helpers/helpers.go

@@ -2,7 +2,10 @@ package helpers
 
 import (
 	"context"
+	"database/sql"
+	"errors"
 	"fmt"
+	"strings"
 
 	"github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/roomserver/auth"
@@ -234,12 +237,73 @@ func CheckServerAllowedToSeeEvent(
 	ctx context.Context, db storage.Database, info *types.RoomInfo, eventID string, serverName gomatrixserverlib.ServerName, isServerInRoom bool,
 ) (bool, error) {
 	stateAtEvent, err := db.GetHistoryVisibilityState(ctx, info, eventID, string(serverName))
-	if err != nil {
+	switch err {
+	case nil:
+		// No error, so continue normally
+	case tables.OptimisationNotSupportedError:
+		// The database engine didn't support this optimisation, so fall back to using
+		// the old and slow method
+		stateAtEvent, err = slowGetHistoryVisibilityState(ctx, db, info, eventID, serverName)
+		if err != nil {
+			return false, err
+		}
+	default:
+		// Something else went wrong
 		return false, err
 	}
 	return auth.IsServerAllowed(serverName, isServerInRoom, stateAtEvent), nil
 }
 
+func slowGetHistoryVisibilityState(
+	ctx context.Context, db storage.Database, info *types.RoomInfo, eventID string, serverName gomatrixserverlib.ServerName,
+) ([]*gomatrixserverlib.Event, error) {
+	roomState := state.NewStateResolution(db, info)
+	stateEntries, err := roomState.LoadStateAtEvent(ctx, eventID)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("roomState.LoadStateAtEvent: %w", err)
+	}
+
+	// Extract all of the event state key NIDs from the room state.
+	var stateKeyNIDs []types.EventStateKeyNID
+	for _, entry := range stateEntries {
+		stateKeyNIDs = append(stateKeyNIDs, entry.EventStateKeyNID)
+	}
+
+	// Then request those state key NIDs from the database.
+	stateKeys, err := db.EventStateKeys(ctx, stateKeyNIDs)
+	if err != nil {
+		return nil, fmt.Errorf("db.EventStateKeys: %w", err)
+	}
+
+	// If the event state key doesn't match the given servername
+	// then we'll filter it out. This does preserve state keys that
+	// are "" since these will contain history visibility etc.
+	for nid, key := range stateKeys {
+		if key != "" && !strings.HasSuffix(key, ":"+string(serverName)) {
+			delete(stateKeys, nid)
+		}
+	}
+
+	// Now filter through all of the state events for the room.
+	// If the state key NID appears in the list of valid state
+	// keys then we'll add it to the list of filtered entries.
+	var filteredEntries []types.StateEntry
+	for _, entry := range stateEntries {
+		if _, ok := stateKeys[entry.EventStateKeyNID]; ok {
+			filteredEntries = append(filteredEntries, entry)
+		}
+	}
+
+	if len(filteredEntries) == 0 {
+		return nil, nil
+	}
+
+	return LoadStateEvents(ctx, db, filteredEntries)
+}
+
 // TODO: Remove this when we have tests to assert correctness of this function
 func ScanEventTree(
 	ctx context.Context, db storage.Database, info *types.RoomInfo, front []string, visited map[string]bool, limit int,

roomserver/storage/sqlite3/state_snapshot_table.go

@@ -62,32 +62,10 @@ const bulkSelectStateBlockNIDsSQL = "" +
 	"SELECT state_snapshot_nid, state_block_nids FROM roomserver_state_snapshots" +
 	" WHERE state_snapshot_nid IN ($1) ORDER BY state_snapshot_nid ASC"
 
-// Looks up both the history visibility event and relevant membership events from
-// a given domain name from a given state snapshot. This is used to optimise the
-// helpers.CheckServerAllowedToSeeEvent function.
-// TODO: There's a sequence scan here because of the hash join strategy, which is
-// probably O(n) on state key entries, so there must be a way to avoid that somehow.
-const bulkSelectStateForHistoryVisibilitySQL = "" +
-	"SELECT event_nid FROM (" +
-	" SELECT event_nid, event_type_nid, event_state_key_nid FROM roomserver_events" +
-	" WHERE (event_type_nid = 5 OR event_type_nid = 7)" +
-	" AND event_nid = ANY(" +
-	"  SELECT UNNEST(event_nids) FROM roomserver_state_block" +
-	"  WHERE state_block_nid = ANY(" +
-	"   SELECT UNNEST(state_block_nids) FROM roomserver_state_snapshots" +
-	"   WHERE state_snapshot_nid = $1" +
-	"  )" +
-	" )" +
-	") AS roomserver_events" +
-	" INNER JOIN roomserver_event_state_keys" +
-	"  ON roomserver_events.event_state_key_nid = roomserver_event_state_keys.event_state_key_nid" +
-	"  AND (event_type_nid = 7 OR event_state_key LIKE '%:' || $2);"
-
 type stateSnapshotStatements struct {
-	db                                      *sql.DB
-	insertStateStmt                         *sql.Stmt
-	bulkSelectStateBlockNIDsStmt            *sql.Stmt
-	bulkSelectStateForHistoryVisibilityStmt *sql.Stmt
+	db                           *sql.DB
+	insertStateStmt              *sql.Stmt
+	bulkSelectStateBlockNIDsStmt *sql.Stmt
 }
 
 func CreateStateSnapshotTable(db *sql.DB) error {
@@ -103,7 +81,6 @@ func PrepareStateSnapshotTable(db *sql.DB) (tables.StateSnapshot, error) {
 	return s, sqlutil.StatementList{
 		{&s.insertStateStmt, insertStateSQL},
 		{&s.bulkSelectStateBlockNIDsStmt, bulkSelectStateBlockNIDsSQL},
-		{&s.bulkSelectStateForHistoryVisibilityStmt, bulkSelectStateForHistoryVisibilitySQL},
 	}.Prepare(db)
 }
 
@@ -167,22 +144,5 @@ func (s *stateSnapshotStatements) BulkSelectStateBlockNIDs(
 func (s *stateSnapshotStatements) BulkSelectStateForHistoryVisibility(
 	ctx context.Context, txn *sql.Tx, stateSnapshotNID types.StateSnapshotNID, domain string,
 ) ([]types.EventNID, error) {
-	stmt := sqlutil.TxStmt(txn, s.bulkSelectStateForHistoryVisibilityStmt)
-	rows, err := stmt.QueryContext(ctx, stateSnapshotNID, domain)
-	if err != nil {
-		return nil, err
-	}
-	defer rows.Close() // nolint: errcheck
-	results := make([]types.EventNID, 0, 16)
-	for i := 0; rows.Next(); i++ {
-		var eventNID types.EventNID
-		if err = rows.Scan(&eventNID); err != nil {
-			return nil, err
-		}
-		results = append(results, eventNID)
-	}
-	if err = rows.Err(); err != nil {
-		return nil, err
-	}
-	return results, nil
+	return nil, tables.OptimisationNotSupportedError
 }

roomserver/storage/tables/interface.go

@@ -3,12 +3,15 @@ package tables
 import (
 	"context"
 	"database/sql"
+	"errors"
 
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/tidwall/gjson"
 )
 
+var OptimisationNotSupportedError = errors.New("optimisation not supported")
+
 type EventJSONPair struct {
 	EventNID  types.EventNID
 	EventJSON []byte