Component-wide TransactionWriters (#1290)

* Offset updates take place using TransactionWriter

* Refactor TransactionWriter in current state server

* Refactor TransactionWriter in federation sender

* Refactor TransactionWriter in key server

* Refactor TransactionWriter in media API

* Refactor TransactionWriter in server key API

* Refactor TransactionWriter in sync API

* Refactor TransactionWriter in user API

* Fix deadlocking Sync API tests

* Un-deadlock device database

* Fix appservice API

* Rename TransactionWriters to Writers

* Move writers up a layer in sync API

* Document sqlutil.Writer interface

* Add note to Writer documentation

appservice/storage/postgres/storage.go

@@ -32,6 +32,7 @@ type Database struct {
 	events eventsStatements
 	txnID  txnStatements
 	db     *sql.DB
+	writer sqlutil.Writer
 }
 
 // NewDatabase opens a new database
@@ -41,10 +42,11 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	if result.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
+	result.writer = sqlutil.NewDummyWriter()
 	if err = result.prepare(); err != nil {
 		return nil, err
 	}
-	if err = result.PartitionOffsetStatements.Prepare(result.db, "appservice"); err != nil {
+	if err = result.PartitionOffsetStatements.Prepare(result.db, result.writer, "appservice"); err != nil {
 		return nil, err
 	}
 	return &result, nil

appservice/storage/sqlite3/appservice_events_table.go

@@ -67,7 +67,7 @@ const (
 
 type eventsStatements struct {
 	db                                     *sql.DB
-	writer                                 sqlutil.TransactionWriter
+	writer                                 sqlutil.Writer
 	selectEventsByApplicationServiceIDStmt *sql.Stmt
 	countEventsByApplicationServiceIDStmt  *sql.Stmt
 	insertEventStmt                        *sql.Stmt
@@ -75,9 +75,9 @@ type eventsStatements struct {
 	deleteEventsBeforeAndIncludingIDStmt   *sql.Stmt
 }
 
-func (s *eventsStatements) prepare(db *sql.DB) (err error) {
+func (s *eventsStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 	_, err = db.Exec(appserviceEventsSchema)
 	if err != nil {
 		return

appservice/storage/sqlite3/storage.go

@@ -32,6 +32,7 @@ type Database struct {
 	events eventsStatements
 	txnID  txnStatements
 	db     *sql.DB
+	writer sqlutil.Writer
 }
 
 // NewDatabase opens a new database
@@ -41,21 +42,22 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	if result.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
+	result.writer = sqlutil.NewExclusiveWriter()
 	if err = result.prepare(); err != nil {
 		return nil, err
 	}
-	if err = result.PartitionOffsetStatements.Prepare(result.db, "appservice"); err != nil {
+	if err = result.PartitionOffsetStatements.Prepare(result.db, result.writer, "appservice"); err != nil {
 		return nil, err
 	}
 	return &result, nil
 }
 
 func (d *Database) prepare() error {
-	if err := d.events.prepare(d.db); err != nil {
+	if err := d.events.prepare(d.db, d.writer); err != nil {
 		return err
 	}
 
-	return d.txnID.prepare(d.db)
+	return d.txnID.prepare(d.db, d.writer)
 }
 
 // StoreEvent takes in a gomatrixserverlib.HeaderedEvent and stores it in the database

appservice/storage/sqlite3/txn_id_counter_table.go

@@ -38,13 +38,13 @@ const selectTxnIDSQL = `
 
 type txnStatements struct {
 	db              *sql.DB
-	writer          sqlutil.TransactionWriter
+	writer          sqlutil.Writer
 	selectTxnIDStmt *sql.Stmt
 }
 
-func (s *txnStatements) prepare(db *sql.DB) (err error) {
+func (s *txnStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 	_, err = db.Exec(txnIDSchema)
 	if err != nil {
 		return

currentstateserver/storage/postgres/storage.go

@@ -11,6 +11,7 @@ import (
 type Database struct {
 	shared.Database
 	db     *sql.DB
+	writer sqlutil.Writer
 	sqlutil.PartitionOffsetStatements
 }
 
@@ -21,7 +22,8 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
-	if err = d.PartitionOffsetStatements.Prepare(d.db, "currentstate"); err != nil {
+	d.writer = sqlutil.NewDummyWriter()
+	if err = d.PartitionOffsetStatements.Prepare(d.db, d.writer, "currentstate"); err != nil {
 		return nil, err
 	}
 	currRoomState, err := NewPostgresCurrentRoomStateTable(d.db)
@@ -30,6 +32,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	}
 	d.Database = shared.Database{
 		DB:               d.db,
+		Writer:           d.writer,
 		CurrentRoomState: currRoomState,
 	}
 	return &d, nil

currentstateserver/storage/shared/storage.go

@@ -27,6 +27,7 @@ import (
 
 type Database struct {
 	DB               *sql.DB
+	Writer           sqlutil.Writer
 	CurrentRoomState tables.CurrentRoomState
 }
 
@@ -59,7 +60,7 @@ func (d *Database) RedactEvent(ctx context.Context, redactedEventID string, reda
 
 func (d *Database) StoreStateEvents(ctx context.Context, addStateEvents []gomatrixserverlib.HeaderedEvent,
 	removeStateEventIDs []string) error {
-	return sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
 		// remove first, then add, as we do not ever delete state, but do replace state which is a remove followed by an add.
 		for _, eventID := range removeStateEventIDs {
 			if err := d.CurrentRoomState.DeleteRoomStateByEventID(ctx, txn, eventID); err != nil {

currentstateserver/storage/sqlite3/current_room_state_table.go

@@ -83,7 +83,7 @@ const selectKnownUsersSQL = "" +
 
 type currentRoomStateStatements struct {
 	db                               *sql.DB
-	writer                           sqlutil.TransactionWriter
+	writer                           sqlutil.Writer
 	upsertRoomStateStmt              *sql.Stmt
 	deleteRoomStateByEventIDStmt     *sql.Stmt
 	selectRoomIDsWithMembershipStmt  *sql.Stmt
@@ -96,7 +96,7 @@ type currentRoomStateStatements struct {
 func NewSqliteCurrentRoomStateTable(db *sql.DB) (tables.CurrentRoomState, error) {
 	s := &currentRoomStateStatements{
 		db:     db,
-		writer: sqlutil.NewTransactionWriter(),
+		writer: sqlutil.NewExclusiveWriter(),
 	}
 	_, err := db.Exec(currentRoomStateSchema)
 	if err != nil {

currentstateserver/storage/sqlite3/storage.go

@@ -11,6 +11,7 @@ import (
 type Database struct {
 	shared.Database
 	db     *sql.DB
+	writer sqlutil.Writer
 	sqlutil.PartitionOffsetStatements
 }
 
@@ -22,7 +23,8 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
-	if err = d.PartitionOffsetStatements.Prepare(d.db, "currentstate"); err != nil {
+	d.writer = sqlutil.NewExclusiveWriter()
+	if err = d.PartitionOffsetStatements.Prepare(d.db, d.writer, "currentstate"); err != nil {
 		return nil, err
 	}
 	currRoomState, err := NewSqliteCurrentRoomStateTable(d.db)
@@ -31,6 +33,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	}
 	d.Database = shared.Database{
 		DB:               d.db,
+		Writer:           d.writer,
 		CurrentRoomState: currRoomState,
 	}
 	return &d, nil

federationsender/storage/postgres/storage.go

@@ -28,6 +28,7 @@ type Database struct {
 	shared.Database
 	sqlutil.PartitionOffsetStatements
 	db     *sql.DB
+	writer sqlutil.Writer
 }
 
 // NewDatabase opens a new database
@@ -37,6 +38,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
+	d.writer = sqlutil.NewDummyWriter()
 	joinedHosts, err := NewPostgresJoinedHostsTable(d.db)
 	if err != nil {
 		return nil, err
@@ -63,6 +65,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	}
 	d.Database = shared.Database{
 		DB:                          d.db,
+		Writer:                      d.writer,
 		FederationSenderJoinedHosts: joinedHosts,
 		FederationSenderQueuePDUs:   queuePDUs,
 		FederationSenderQueueEDUs:   queueEDUs,
@@ -70,7 +73,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 		FederationSenderRooms:       rooms,
 		FederationSenderBlacklist:   blacklist,
 	}
-	if err = d.PartitionOffsetStatements.Prepare(d.db, "federationsender"); err != nil {
+	if err = d.PartitionOffsetStatements.Prepare(d.db, d.writer, "federationsender"); err != nil {
 		return nil, err
 	}
 	return &d, nil

federationsender/storage/shared/storage.go

@@ -28,6 +28,7 @@ import (
 
 type Database struct {
 	DB                          *sql.DB
+	Writer                      sqlutil.Writer
 	FederationSenderQueuePDUs   tables.FederationSenderQueuePDUs
 	FederationSenderQueueEDUs   tables.FederationSenderQueueEDUs
 	FederationSenderQueueJSON   tables.FederationSenderQueueJSON
@@ -64,7 +65,7 @@ func (d *Database) UpdateRoom(
 	addHosts []types.JoinedHost,
 	removeHosts []string,
 ) (joinedHosts []types.JoinedHost, err error) {
-	err = sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
 		err = d.FederationSenderRooms.InsertRoom(ctx, txn, roomID)
 		if err != nil {
 			return err
@@ -133,7 +134,12 @@ func (d *Database) GetJoinedHostsForRooms(ctx context.Context, roomIDs []string)
 func (d *Database) StoreJSON(
 	ctx context.Context, js string,
 ) (*Receipt, error) {
-	nid, err := d.FederationSenderQueueJSON.InsertQueueJSON(ctx, nil, js)
+	var nid int64
+	var err error
+	_ = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		nid, err = d.FederationSenderQueueJSON.InsertQueueJSON(ctx, txn, js)
+		return nil
+	})
 	if err != nil {
 		return nil, fmt.Errorf("d.insertQueueJSON: %w", err)
 	}
@@ -143,11 +149,15 @@ func (d *Database) StoreJSON(
 }
 
 func (d *Database) AddServerToBlacklist(serverName gomatrixserverlib.ServerName) error {
-	return d.FederationSenderBlacklist.InsertBlacklist(context.TODO(), nil, serverName)
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.FederationSenderBlacklist.InsertBlacklist(context.TODO(), txn, serverName)
+	})
 }
 
 func (d *Database) RemoveServerFromBlacklist(serverName gomatrixserverlib.ServerName) error {
-	return d.FederationSenderBlacklist.DeleteBlacklist(context.TODO(), nil, serverName)
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.FederationSenderBlacklist.DeleteBlacklist(context.TODO(), txn, serverName)
+	})
 }
 
 func (d *Database) IsServerBlacklisted(serverName gomatrixserverlib.ServerName) (bool, error) {

federationsender/storage/sqlite3/blacklist_table.go

@@ -42,7 +42,6 @@ const deleteBlacklistSQL = "" +
 
 type blacklistStatements struct {
 	db                  *sql.DB
-	writer              sqlutil.TransactionWriter
 	insertBlacklistStmt *sql.Stmt
 	selectBlacklistStmt *sql.Stmt
 	deleteBlacklistStmt *sql.Stmt
@@ -51,7 +50,6 @@ type blacklistStatements struct {
 func NewSQLiteBlacklistTable(db *sql.DB) (s *blacklistStatements, err error) {
 	s = &blacklistStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err = db.Exec(blacklistSchema)
 	if err != nil {
@@ -75,11 +73,9 @@ func NewSQLiteBlacklistTable(db *sql.DB) (s *blacklistStatements, err error) {
 func (s *blacklistStatements) InsertBlacklist(
 	ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.insertBlacklistStmt)
 	_, err := stmt.ExecContext(ctx, serverName)
 	return err
-	})
 }
 
 // selectRoomForUpdate locks the row for the room and returns the last_event_id.
@@ -105,9 +101,7 @@ func (s *blacklistStatements) SelectBlacklist(
 func (s *blacklistStatements) DeleteBlacklist(
 	ctx context.Context, txn *sql.Tx, serverName gomatrixserverlib.ServerName,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.deleteBlacklistStmt)
 	_, err := stmt.ExecContext(ctx, serverName)
 	return err
-	})
 }

federationsender/storage/sqlite3/joined_hosts_table.go

@@ -65,7 +65,6 @@ const selectJoinedHostsForRoomsSQL = "" +
 
 type joinedHostsStatements struct {
 	db                       *sql.DB
-	writer                   sqlutil.TransactionWriter
 	insertJoinedHostsStmt    *sql.Stmt
 	deleteJoinedHostsStmt    *sql.Stmt
 	selectJoinedHostsStmt    *sql.Stmt
@@ -76,7 +75,6 @@ type joinedHostsStatements struct {
 func NewSQLiteJoinedHostsTable(db *sql.DB) (s *joinedHostsStatements, err error) {
 	s = &joinedHostsStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err = db.Exec(joinedHostsSchema)
 	if err != nil {
@@ -103,17 +101,14 @@ func (s *joinedHostsStatements) InsertJoinedHosts(
 	roomID, eventID string,
 	serverName gomatrixserverlib.ServerName,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.insertJoinedHostsStmt)
 	_, err := stmt.ExecContext(ctx, roomID, eventID, serverName)
 	return err
-	})
 }
 
 func (s *joinedHostsStatements) DeleteJoinedHosts(
 	ctx context.Context, txn *sql.Tx, eventIDs []string,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	for _, eventID := range eventIDs {
 		stmt := sqlutil.TxStmt(txn, s.deleteJoinedHostsStmt)
 		if _, err := stmt.ExecContext(ctx, eventID); err != nil {
@@ -121,7 +116,6 @@ func (s *joinedHostsStatements) DeleteJoinedHosts(
 		}
 	}
 	return nil
-	})
 }
 
 func (s *joinedHostsStatements) SelectJoinedHostsWithTx(

federationsender/storage/sqlite3/queue_edus_table.go

@@ -64,7 +64,6 @@ const selectQueueServerNamesSQL = "" +
 
 type queueEDUsStatements struct {
 	db                                   *sql.DB
-	writer                               sqlutil.TransactionWriter
 	insertQueueEDUStmt                   *sql.Stmt
 	selectQueueEDUStmt                   *sql.Stmt
 	selectQueueEDUReferenceJSONCountStmt *sql.Stmt
@@ -75,7 +74,6 @@ type queueEDUsStatements struct {
 func NewSQLiteQueueEDUsTable(db *sql.DB) (s *queueEDUsStatements, err error) {
 	s = &queueEDUsStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err = db.Exec(queueEDUsSchema)
 	if err != nil {
@@ -106,7 +104,6 @@ func (s *queueEDUsStatements) InsertQueueEDU(
 	serverName gomatrixserverlib.ServerName,
 	nid int64,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.insertQueueEDUStmt)
 	_, err := stmt.ExecContext(
 		ctx,
@@ -115,7 +112,6 @@ func (s *queueEDUsStatements) InsertQueueEDU(
 		nid,        // JSON blob NID
 	)
 	return err
-	})
 }
 
 func (s *queueEDUsStatements) DeleteQueueEDUs(
@@ -135,11 +131,9 @@ func (s *queueEDUsStatements) DeleteQueueEDUs(
 		params[k+1] = v
 	}
 
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, deleteStmt)
-		_, err := stmt.ExecContext(ctx, params...)
+	_, err = stmt.ExecContext(ctx, params...)
 	return err
-	})
 }
 
 func (s *queueEDUsStatements) SelectQueueEDUs(

federationsender/storage/sqlite3/queue_json_table.go

@@ -50,7 +50,6 @@ const selectJSONSQL = "" +
 
 type queueJSONStatements struct {
 	db             *sql.DB
-	writer         sqlutil.TransactionWriter
 	insertJSONStmt *sql.Stmt
 	//deleteJSONStmt *sql.Stmt - prepared at runtime due to variadic
 	//selectJSONStmt *sql.Stmt - prepared at runtime due to variadic
@@ -59,7 +58,6 @@ type queueJSONStatements struct {
 func NewSQLiteQueueJSONTable(db *sql.DB) (s *queueJSONStatements, err error) {
 	s = &queueJSONStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err = db.Exec(queueJSONSchema)
 	if err != nil {
@@ -74,18 +72,15 @@ func NewSQLiteQueueJSONTable(db *sql.DB) (s *queueJSONStatements, err error) {
 func (s *queueJSONStatements) InsertQueueJSON(
 	ctx context.Context, txn *sql.Tx, json string,
 ) (lastid int64, err error) {
-	err = s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.insertJSONStmt)
 	res, err := stmt.ExecContext(ctx, json)
 	if err != nil {
-			return fmt.Errorf("stmt.QueryContext: %w", err)
+		return 0, fmt.Errorf("stmt.QueryContext: %w", err)
 	}
 	lastid, err = res.LastInsertId()
 	if err != nil {
-			return fmt.Errorf("res.LastInsertId: %w", err)
+		return 0, fmt.Errorf("res.LastInsertId: %w", err)
 	}
-		return nil
-	})
 	return
 }
 
@@ -103,11 +98,9 @@ func (s *queueJSONStatements) DeleteQueueJSON(
 		iNIDs[k] = v
 	}
 
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, deleteStmt)
 	_, err = stmt.ExecContext(ctx, iNIDs...)
 	return err
-	})
 }
 
 func (s *queueJSONStatements) SelectQueueJSON(

federationsender/storage/sqlite3/queue_pdus_table.go

@@ -71,7 +71,6 @@ const selectQueuePDUsServerNamesSQL = "" +
 
 type queuePDUsStatements struct {
 	db                                *sql.DB
-	writer                            sqlutil.TransactionWriter
 	insertQueuePDUStmt                *sql.Stmt
 	selectQueueNextTransactionIDStmt  *sql.Stmt
 	selectQueuePDUsByTransactionStmt  *sql.Stmt
@@ -84,7 +83,6 @@ type queuePDUsStatements struct {
 func NewSQLiteQueuePDUsTable(db *sql.DB) (s *queuePDUsStatements, err error) {
 	s = &queuePDUsStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err = db.Exec(queuePDUsSchema)
 	if err != nil {
@@ -121,7 +119,6 @@ func (s *queuePDUsStatements) InsertQueuePDU(
 	serverName gomatrixserverlib.ServerName,
 	nid int64,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.insertQueuePDUStmt)
 	_, err := stmt.ExecContext(
 		ctx,
@@ -130,7 +127,6 @@ func (s *queuePDUsStatements) InsertQueuePDU(
 		nid,           // JSON blob NID
 	)
 	return err
-	})
 }
 
 func (s *queuePDUsStatements) DeleteQueuePDUs(
@@ -150,11 +146,9 @@ func (s *queuePDUsStatements) DeleteQueuePDUs(
 		params[k+1] = v
 	}
 
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, deleteStmt)
-		_, err := stmt.ExecContext(ctx, params...)
+	_, err = stmt.ExecContext(ctx, params...)
 	return err
-	})
 }
 
 func (s *queuePDUsStatements) SelectQueuePDUNextTransactionID(

federationsender/storage/sqlite3/room_table.go

@@ -44,7 +44,6 @@ const updateRoomSQL = "" +
 
 type roomStatements struct {
 	db                      *sql.DB
-	writer                  sqlutil.TransactionWriter
 	insertRoomStmt          *sql.Stmt
 	selectRoomForUpdateStmt *sql.Stmt
 	updateRoomStmt          *sql.Stmt
@@ -53,7 +52,6 @@ type roomStatements struct {
 func NewSQLiteRoomsTable(db *sql.DB) (s *roomStatements, err error) {
 	s = &roomStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err = db.Exec(roomSchema)
 	if err != nil {
@@ -77,10 +75,8 @@ func NewSQLiteRoomsTable(db *sql.DB) (s *roomStatements, err error) {
 func (s *roomStatements) InsertRoom(
 	ctx context.Context, txn *sql.Tx, roomID string,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	_, err := sqlutil.TxStmt(txn, s.insertRoomStmt).ExecContext(ctx, roomID)
 	return err
-	})
 }
 
 // selectRoomForUpdate locks the row for the room and returns the last_event_id.
@@ -103,9 +99,7 @@ func (s *roomStatements) SelectRoomForUpdate(
 func (s *roomStatements) UpdateRoom(
 	ctx context.Context, txn *sql.Tx, roomID, lastEventID string,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.updateRoomStmt)
 	_, err := stmt.ExecContext(ctx, roomID, lastEventID)
 	return err
-	})
 }

federationsender/storage/sqlite3/storage.go

@@ -30,6 +30,7 @@ type Database struct {
 	shared.Database
 	sqlutil.PartitionOffsetStatements
 	db     *sql.DB
+	writer sqlutil.Writer
 }
 
 // NewDatabase opens a new database
@@ -39,6 +40,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
+	d.writer = sqlutil.NewExclusiveWriter()
 	joinedHosts, err := NewSQLiteJoinedHostsTable(d.db)
 	if err != nil {
 		return nil, err
@@ -65,6 +67,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 	}
 	d.Database = shared.Database{
 		DB:                          d.db,
+		Writer:                      d.writer,
 		FederationSenderJoinedHosts: joinedHosts,
 		FederationSenderQueuePDUs:   queuePDUs,
 		FederationSenderQueueEDUs:   queueEDUs,
@@ -72,7 +75,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*Database, error) {
 		FederationSenderRooms:       rooms,
 		FederationSenderBlacklist:   blacklist,
 	}
-	if err = d.PartitionOffsetStatements.Prepare(d.db, "federationsender"); err != nil {
+	if err = d.PartitionOffsetStatements.Prepare(d.db, d.writer, "federationsender"); err != nil {
 		return nil, err
 	}
 	return &d, nil

internal/sqlutil/partition_offset_table.go

@@ -53,6 +53,8 @@ const upsertPartitionOffsetsSQL = "" +
 
 // PartitionOffsetStatements represents a set of statements that can be run on a partition_offsets table.
 type PartitionOffsetStatements struct {
+	db                         *sql.DB
+	writer                     Writer
 	selectPartitionOffsetsStmt *sql.Stmt
 	upsertPartitionOffsetStmt  *sql.Stmt
 }
@@ -60,7 +62,9 @@ type PartitionOffsetStatements struct {
 // Prepare converts the raw SQL statements into prepared statements.
 // Takes a prefix to prepend to the table name used to store the partition offsets.
 // This allows multiple components to share the same database schema.
-func (s *PartitionOffsetStatements) Prepare(db *sql.DB, prefix string) (err error) {
+func (s *PartitionOffsetStatements) Prepare(db *sql.DB, writer Writer, prefix string) (err error) {
+	s.db = db
+	s.writer = writer
 	_, err = db.Exec(strings.Replace(partitionOffsetsSchema, "${prefix}", prefix, -1))
 	if err != nil {
 		return
@@ -121,6 +125,9 @@ func (s *PartitionOffsetStatements) selectPartitionOffsets(
 func (s *PartitionOffsetStatements) upsertPartitionOffset(
 	ctx context.Context, topic string, partition int32, offset int64,
 ) error {
-	_, err := s.upsertPartitionOffsetStmt.ExecContext(ctx, topic, partition, offset)
+	return s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
+		stmt := TxStmt(txn, s.upsertPartitionOffsetStmt)
+		_, err := stmt.ExecContext(ctx, topic, partition, offset)
 		return err
+	})
 }

internal/sqlutil/sql.go

@@ -103,7 +103,3 @@ func SQLiteDriverName() string {
 	}
 	return "sqlite3"
 }
-
-type TransactionWriter interface {
-	Do(db *sql.DB, txn *sql.Tx, f func(txn *sql.Tx) error) error
-}

internal/sqlutil/writer.go

@@ -0,0 +1,46 @@
+package sqlutil
+
+import "database/sql"
+
+// The Writer interface is designed to solve the problem of how
+// to handle database writes for database engines that don't allow
+// concurrent writes, e.g. SQLite.
+//
+// The interface has a single Do function which takes an optional
+// database parameter, an optional transaction parameter and a
+// required function parameter. The Writer will call the function
+// provided when it is safe to do so, optionally providing a
+// transaction to use.
+//
+// Depending on the combination of parameters provided, the Writer
+// will behave in one of three ways:
+//
+// 1. `db` provided, `txn` provided:
+//
+// The Writer will call f() when it is safe to do so. The supplied
+// "txn" will ALWAYS be passed through to f(). Use this when you
+// already have a transaction open.
+//
+// 2. `db` provided, `txn` not provided (nil):
+//
+// The Writer will open a new transaction on the provided database
+// and then will call f() when it is safe to do so. The new
+// transaction will ALWAYS be passed through to f(). Use this if
+// you plan to perform more than one SQL query within f().
+//
+// 3. `db` not provided (nil), `txn` not provided (nil):
+//
+// The Writer will call f() when it is safe to do so, but will
+// not make any attempt to open a new database transaction or to
+// pass through an existing one. The "txn" parameter within f()
+// will ALWAYS be nil in this mode. This is useful if you just
+// want to perform a single query on an already-prepared statement
+// without the overhead of opening a new transaction to do it in.
+//
+// You MUST take particular care not to call Do() from within f()
+// on the same Writer, or it will likely result in a deadlock.
+type Writer interface {
+	// Queue up one or more database write operations within the
+	// provided function to be executed when it is safe to do so.
+	Do(db *sql.DB, txn *sql.Tx, f func(txn *sql.Tx) error) error
+}

internal/sqlutil/writer_dummy.go

@@ -4,15 +4,21 @@ import (
 	"database/sql"
 )
 
-type DummyTransactionWriter struct {
+// DummyWriter implements sqlutil.Writer.
+// The DummyWriter is designed to allow reuse of the sqlutil.Writer
+// interface but, unlike ExclusiveWriter, it will not guarantee
+// writer exclusivity. This is fine in PostgreSQL where overlapping
+// transactions and writes are acceptable.
+type DummyWriter struct {
 }
 
-func NewDummyTransactionWriter() TransactionWriter {
+// NewDummyWriter returns a new dummy writer.
-	return &DummyTransactionWriter{}
+func NewDummyWriter() Writer {
+	return &DummyWriter{}
 }
 
-func (w *DummyTransactionWriter) Do(db *sql.DB, txn *sql.Tx, f func(txn *sql.Tx) error) error {
+func (w *DummyWriter) Do(db *sql.DB, txn *sql.Tx, f func(txn *sql.Tx) error) error {
-	if txn == nil {
+	if db != nil && txn == nil {
 		return WithTransaction(db, func(txn *sql.Tx) error {
 			return f(txn)
 		})

internal/sqlutil/writer_exclusive.go

@@ -7,16 +7,17 @@ import (
 	"go.uber.org/atomic"
 )
 
-// ExclusiveTransactionWriter allows queuing database writes so that you don't
+// ExclusiveWriter implements sqlutil.Writer.
+// ExclusiveWriter allows queuing database writes so that you don't
 // contend on database locks in, e.g. SQLite. Only one task will run
-// at a time on a given ExclusiveTransactionWriter.
+// at a time on a given ExclusiveWriter.
-type ExclusiveTransactionWriter struct {
+type ExclusiveWriter struct {
 	running atomic.Bool
 	todo    chan transactionWriterTask
 }
 
-func NewTransactionWriter() TransactionWriter {
+func NewExclusiveWriter() Writer {
-	return &ExclusiveTransactionWriter{
+	return &ExclusiveWriter{
 		todo: make(chan transactionWriterTask),
 	}
 }
@@ -34,7 +35,7 @@ type transactionWriterTask struct {
 // txn parameter if one is supplied, and if not, will take out a
 // new transaction from the database supplied in the database
 // parameter. Either way, this will block until the task is done.
-func (w *ExclusiveTransactionWriter) Do(db *sql.DB, txn *sql.Tx, f func(txn *sql.Tx) error) error {
+func (w *ExclusiveWriter) Do(db *sql.DB, txn *sql.Tx, f func(txn *sql.Tx) error) error {
 	if w.todo == nil {
 		return errors.New("not initialised")
 	}
@@ -55,20 +56,20 @@ func (w *ExclusiveTransactionWriter) Do(db *sql.DB, txn *sql.Tx, f func(txn *sql
 // of these goroutines will run at a time. A transaction will be
 // opened using the database object from the task and then this will
 // be passed as a parameter to the task function.
-func (w *ExclusiveTransactionWriter) run() {
+func (w *ExclusiveWriter) run() {
 	if !w.running.CAS(false, true) {
 		return
 	}
 	defer w.running.Store(false)
 	for task := range w.todo {
-		if task.txn != nil {
+		if task.db != nil && task.txn != nil {
 			task.wait <- task.f(task.txn)
-		} else if task.db != nil {
+		} else if task.db != nil && task.txn == nil {
 			task.wait <- WithTransaction(task.db, func(txn *sql.Tx) error {
 				return task.f(txn)
 			})
 		} else {
-			panic("expected database or transaction but got neither")
+			task.wait <- task.f(nil)
 		}
 		close(task.wait)
 	}

keyserver/storage/sqlite3/device_keys_table.go

@@ -63,7 +63,7 @@ const deleteAllDeviceKeysSQL = "" +
 
 type deviceKeysStatements struct {
 	db                         *sql.DB
-	writer                     sqlutil.TransactionWriter
+	writer                     sqlutil.Writer
 	upsertDeviceKeysStmt       *sql.Stmt
 	selectDeviceKeysStmt       *sql.Stmt
 	selectBatchDeviceKeysStmt  *sql.Stmt
@@ -71,10 +71,10 @@ type deviceKeysStatements struct {
 	deleteAllDeviceKeysStmt    *sql.Stmt
 }
 
-func NewSqliteDeviceKeysTable(db *sql.DB) (tables.DeviceKeys, error) {
+func NewSqliteDeviceKeysTable(db *sql.DB, writer sqlutil.Writer) (tables.DeviceKeys, error) {
 	s := &deviceKeysStatements{
 		db:     db,
-		writer: sqlutil.NewTransactionWriter(),
+		writer: writer,
 	}
 	_, err := db.Exec(deviceKeysSchema)
 	if err != nil {

keyserver/storage/sqlite3/key_changes_table.go

@@ -52,15 +52,15 @@ const selectKeyChangesSQL = "" +
 
 type keyChangesStatements struct {
 	db                   *sql.DB
-	writer               sqlutil.TransactionWriter
+	writer               sqlutil.Writer
 	upsertKeyChangeStmt  *sql.Stmt
 	selectKeyChangesStmt *sql.Stmt
 }
 
-func NewSqliteKeyChangesTable(db *sql.DB) (tables.KeyChanges, error) {
+func NewSqliteKeyChangesTable(db *sql.DB, writer sqlutil.Writer) (tables.KeyChanges, error) {
 	s := &keyChangesStatements{
 		db:     db,
-		writer: sqlutil.NewTransactionWriter(),
+		writer: writer,
 	}
 	_, err := db.Exec(keyChangesSchema)
 	if err != nil {

keyserver/storage/sqlite3/one_time_keys_table.go

@@ -60,7 +60,7 @@ const selectKeyByAlgorithmSQL = "" +
 
 type oneTimeKeysStatements struct {
 	db                       *sql.DB
-	writer                   sqlutil.TransactionWriter
+	writer                   sqlutil.Writer
 	upsertKeysStmt           *sql.Stmt
 	selectKeysStmt           *sql.Stmt
 	selectKeysCountStmt      *sql.Stmt
@@ -68,10 +68,10 @@ type oneTimeKeysStatements struct {
 	deleteOneTimeKeyStmt     *sql.Stmt
 }
 
-func NewSqliteOneTimeKeysTable(db *sql.DB) (tables.OneTimeKeys, error) {
+func NewSqliteOneTimeKeysTable(db *sql.DB, writer sqlutil.Writer) (tables.OneTimeKeys, error) {
 	s := &oneTimeKeysStatements{
 		db:     db,
-		writer: sqlutil.NewTransactionWriter(),
+		writer: writer,
 	}
 	_, err := db.Exec(oneTimeKeysSchema)
 	if err != nil {

keyserver/storage/sqlite3/stale_device_lists.go

@@ -20,6 +20,7 @@ import (
 	"time"
 
 	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/keyserver/storage/tables"
 	"github.com/matrix-org/gomatrixserverlib"
 )
@@ -49,13 +50,18 @@ const selectStaleDeviceListsSQL = "" +
 	"SELECT user_id FROM keyserver_stale_device_lists WHERE is_stale = $1"
 
 type staleDeviceListsStatements struct {
+	db                                    *sql.DB
+	writer                                sqlutil.Writer
 	upsertStaleDeviceListStmt             *sql.Stmt
 	selectStaleDeviceListsWithDomainsStmt *sql.Stmt
 	selectStaleDeviceListsStmt            *sql.Stmt
 }
 
-func NewSqliteStaleDeviceListsTable(db *sql.DB) (tables.StaleDeviceLists, error) {
+func NewSqliteStaleDeviceListsTable(db *sql.DB, writer sqlutil.Writer) (tables.StaleDeviceLists, error) {
-	s := &staleDeviceListsStatements{}
+	s := &staleDeviceListsStatements{
+		db:     db,
+		writer: writer,
+	}
 	_, err := db.Exec(staleDeviceListsSchema)
 	if err != nil {
 		return nil, err
@@ -77,8 +83,11 @@ func (s *staleDeviceListsStatements) InsertStaleDeviceList(ctx context.Context,
 	if err != nil {
 		return err
 	}
-	_, err = s.upsertStaleDeviceListStmt.ExecContext(ctx, userID, string(domain), isStale, time.Now().Unix())
+	return s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
+		stmt := sqlutil.TxStmt(txn, s.upsertStaleDeviceListStmt)
+		_, err = stmt.ExecContext(ctx, userID, string(domain), isStale, time.Now().Unix())
 		return err
+	})
 }
 
 func (s *staleDeviceListsStatements) SelectUserIDsWithStaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error) {

keyserver/storage/sqlite3/storage.go

@@ -25,19 +25,20 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*shared.Database, error)
 	if err != nil {
 		return nil, err
 	}
-	otk, err := NewSqliteOneTimeKeysTable(db)
+	writer := sqlutil.NewExclusiveWriter()
+	otk, err := NewSqliteOneTimeKeysTable(db, writer)
 	if err != nil {
 		return nil, err
 	}
-	dk, err := NewSqliteDeviceKeysTable(db)
+	dk, err := NewSqliteDeviceKeysTable(db, writer)
 	if err != nil {
 		return nil, err
 	}
-	kc, err := NewSqliteKeyChangesTable(db)
+	kc, err := NewSqliteKeyChangesTable(db, writer)
 	if err != nil {
 		return nil, err
 	}
-	sdl, err := NewSqliteStaleDeviceListsTable(db)
+	sdl, err := NewSqliteStaleDeviceListsTable(db, writer)
 	if err != nil {
 		return nil, err
 	}

mediaapi/storage/sqlite3/media_repository_table.go

@@ -62,14 +62,14 @@ SELECT content_type, file_size_bytes, creation_ts, upload_name, base64hash, user
 
 type mediaStatements struct {
 	db              *sql.DB
-	writer          sqlutil.TransactionWriter
+	writer          sqlutil.Writer
 	insertMediaStmt *sql.Stmt
 	selectMediaStmt *sql.Stmt
 }
 
-func (s *mediaStatements) prepare(db *sql.DB) (err error) {
+func (s *mediaStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 
 	_, err = db.Exec(mediaSchema)
 	if err != nil {

mediaapi/storage/sqlite3/sql.go

@@ -17,6 +17,8 @@ package sqlite3
 
 import (
 	"database/sql"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 )
 
 type statements struct {
@@ -24,11 +26,11 @@ type statements struct {
 	thumbnail thumbnailStatements
 }
 
-func (s *statements) prepare(db *sql.DB) (err error) {
+func (s *statements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
-	if err = s.media.prepare(db); err != nil {
+	if err = s.media.prepare(db, writer); err != nil {
 		return
 	}
-	if err = s.thumbnail.prepare(db); err != nil {
+	if err = s.thumbnail.prepare(db, writer); err != nil {
 		return
 	}
 

mediaapi/storage/sqlite3/storage.go

@@ -31,16 +31,19 @@ import (
 type Database struct {
 	statements statements
 	db         *sql.DB
+	writer     sqlutil.Writer
 }
 
 // Open opens a postgres database.
 func Open(dbProperties *config.DatabaseOptions) (*Database, error) {
-	var d Database
+	d := Database{
+		writer: sqlutil.NewExclusiveWriter(),
+	}
 	var err error
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
-	if err = d.statements.prepare(d.db); err != nil {
+	if err = d.statements.prepare(d.db, d.writer); err != nil {
 		return nil, err
 	}
 	return &d, nil

mediaapi/storage/sqlite3/thumbnail_table.go

@@ -21,6 +21,7 @@ import (
 	"time"
 
 	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/mediaapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
 )
@@ -57,16 +58,20 @@ SELECT content_type, file_size_bytes, creation_ts, width, height, resize_method
 `
 
 type thumbnailStatements struct {
+	db                   *sql.DB
+	writer               sqlutil.Writer
 	insertThumbnailStmt  *sql.Stmt
 	selectThumbnailStmt  *sql.Stmt
 	selectThumbnailsStmt *sql.Stmt
 }
 
-func (s *thumbnailStatements) prepare(db *sql.DB) (err error) {
+func (s *thumbnailStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	_, err = db.Exec(thumbnailSchema)
 	if err != nil {
 		return
 	}
+	s.db = db
+	s.writer = writer
 
 	return statementList{
 		{&s.insertThumbnailStmt, insertThumbnailSQL},
@@ -79,7 +84,9 @@ func (s *thumbnailStatements) insertThumbnail(
 	ctx context.Context, thumbnailMetadata *types.ThumbnailMetadata,
 ) error {
 	thumbnailMetadata.MediaMetadata.CreationTimestamp = types.UnixMs(time.Now().UnixNano() / 1000000)
-	_, err := s.insertThumbnailStmt.ExecContext(
+	return s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
+		stmt := sqlutil.TxStmt(txn, s.insertThumbnailStmt)
+		_, err := stmt.ExecContext(
 			ctx,
 			thumbnailMetadata.MediaMetadata.MediaID,
 			thumbnailMetadata.MediaMetadata.Origin,
@@ -91,6 +98,7 @@ func (s *thumbnailStatements) insertThumbnail(
 			thumbnailMetadata.ThumbnailSize.ResizeMethod,
 		)
 		return err
+	})
 }
 
 func (s *thumbnailStatements) selectThumbnail(

roomserver/storage/postgres/storage.go

@@ -98,7 +98,7 @@ func Open(dbProperties *config.DatabaseOptions) (*Database, error) {
 	}
 	d.Database = shared.Database{
 		DB:                  db,
-		Writer:              sqlutil.NewDummyTransactionWriter(),
+		Writer:              sqlutil.NewDummyWriter(),
 		EventTypesTable:     eventTypes,
 		EventStateKeysTable: eventStateKeys,
 		EventJSONTable:      eventJSON,

roomserver/storage/shared/storage.go

@@ -27,7 +27,7 @@ const redactionsArePermanent = false
 
 type Database struct {
 	DB                  *sql.DB
-	Writer              sqlutil.TransactionWriter
+	Writer              sqlutil.Writer
 	EventsTable         tables.Events
 	EventJSONTable      tables.EventJSON
 	EventTypesTable     tables.EventTypes

roomserver/storage/sqlite3/storage.go

@@ -41,7 +41,7 @@ type Database struct {
 	invites        tables.Invites
 	membership     tables.Membership
 	db             *sql.DB
-	writer         sqlutil.TransactionWriter
+	writer         sqlutil.Writer
 }
 
 // Open a sqlite database.
@@ -52,7 +52,7 @@ func Open(dbProperties *config.DatabaseOptions) (*Database, error) {
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
-	d.writer = sqlutil.NewTransactionWriter()
+	d.writer = sqlutil.NewExclusiveWriter()
 	//d.db.Exec("PRAGMA journal_mode=WAL;")
 	//d.db.Exec("PRAGMA read_uncommitted = true;")
 
@@ -120,7 +120,7 @@ func Open(dbProperties *config.DatabaseOptions) (*Database, error) {
 	}
 	d.Database = shared.Database{
 		DB:                  d.db,
-		Writer:              sqlutil.NewTransactionWriter(),
+		Writer:              sqlutil.NewExclusiveWriter(),
 		EventsTable:         d.events,
 		EventTypesTable:     d.eventTypes,
 		EventStateKeysTable: d.eventStateKeys,

serverkeyapi/storage/sqlite3/keydb.go

@@ -30,6 +30,7 @@ import (
 // A Database implements gomatrixserverlib.KeyDatabase and is used to store
 // the public keys for other matrix servers.
 type Database struct {
+	writer     sqlutil.Writer
 	statements serverKeyStatements
 }
 
@@ -47,8 +48,10 @@ func NewDatabase(
 	if err != nil {
 		return nil, err
 	}
-	d := &Database{}
+	d := &Database{
-	err = d.statements.prepare(db)
+		writer: sqlutil.NewExclusiveWriter(),
+	}
+	err = d.statements.prepare(db, d.writer)
 	if err != nil {
 		return nil, err
 	}

serverkeyapi/storage/sqlite3/server_key_table.go

@@ -63,14 +63,14 @@ const upsertServerKeysSQL = "" +
 
 type serverKeyStatements struct {
 	db                       *sql.DB
-	writer                   sqlutil.TransactionWriter
+	writer                   sqlutil.Writer
 	bulkSelectServerKeysStmt *sql.Stmt
 	upsertServerKeysStmt     *sql.Stmt
 }
 
-func (s *serverKeyStatements) prepare(db *sql.DB) (err error) {
+func (s *serverKeyStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 	_, err = db.Exec(serverKeysSchema)
 	if err != nil {
 		return

syncapi/storage/postgres/syncserver.go

@@ -31,6 +31,7 @@ import (
 type SyncServerDatasource struct {
 	shared.Database
 	db     *sql.DB
+	writer sqlutil.Writer
 	sqlutil.PartitionOffsetStatements
 }
 
@@ -41,7 +42,8 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*SyncServerDatasource, e
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
-	if err = d.PartitionOffsetStatements.Prepare(d.db, "syncapi"); err != nil {
+	d.writer = sqlutil.NewDummyWriter()
+	if err = d.PartitionOffsetStatements.Prepare(d.db, d.writer, "syncapi"); err != nil {
 		return nil, err
 	}
 	accountData, err := NewPostgresAccountDataTable(d.db)
@@ -78,6 +80,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*SyncServerDatasource, e
 	}
 	d.Database = shared.Database{
 		DB:                  d.db,
+		Writer:              sqlutil.NewDummyWriter(),
 		Invites:             invites,
 		AccountData:         accountData,
 		OutputEvents:        events,
@@ -86,7 +89,6 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*SyncServerDatasource, e
 		BackwardExtremities: backwardExtremities,
 		Filter:              filter,
 		SendToDevice:        sendToDevice,
-		SendToDeviceWriter:  sqlutil.NewTransactionWriter(),
 		EDUCache:            cache.New(),
 	}
 	return &d, nil

syncapi/storage/shared/syncserver.go

@@ -37,6 +37,7 @@ import (
 // For now this contains the shared functions
 type Database struct {
 	DB                  *sql.DB
+	Writer              sqlutil.Writer
 	Invites             tables.Invites
 	AccountData         tables.AccountData
 	OutputEvents        tables.Events
@@ -45,7 +46,6 @@ type Database struct {
 	BackwardExtremities tables.BackwardsExtremities
 	SendToDevice        tables.SendToDevice
 	Filter              tables.Filter
-	SendToDeviceWriter  sqlutil.TransactionWriter
 	EDUCache            *cache.EDUCache
 }
 
@@ -129,10 +129,7 @@ func (d *Database) GetStateEvent(
 func (d *Database) GetStateEventsForRoom(
 	ctx context.Context, roomID string, stateFilter *gomatrixserverlib.StateFilter,
 ) (stateEvents []gomatrixserverlib.HeaderedEvent, err error) {
-	err = sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
+	stateEvents, err = d.CurrentRoomState.SelectCurrentState(ctx, nil, roomID, stateFilter)
-		stateEvents, err = d.CurrentRoomState.SelectCurrentState(ctx, txn, roomID, stateFilter)
-		return err
-	})
 	return
 }
 
@@ -171,9 +168,9 @@ func (d *Database) SyncStreamPosition(ctx context.Context) (types.StreamPosition
 func (d *Database) AddInviteEvent(
 	ctx context.Context, inviteEvent gomatrixserverlib.HeaderedEvent,
 ) (sp types.StreamPosition, err error) {
-	err = sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
+	_ = d.Writer.Do(nil, nil, func(_ *sql.Tx) error {
-		sp, err = d.Invites.InsertInviteEvent(ctx, txn, inviteEvent)
+		sp, err = d.Invites.InsertInviteEvent(ctx, nil, inviteEvent)
-		return err
+		return nil
 	})
 	return
 }
@@ -182,8 +179,12 @@ func (d *Database) AddInviteEvent(
 // Returns an error if there was a problem communicating with the database.
 func (d *Database) RetireInviteEvent(
 	ctx context.Context, inviteEventID string,
-) (types.StreamPosition, error) {
+) (sp types.StreamPosition, err error) {
-	return d.Invites.DeleteInviteEvent(ctx, inviteEventID)
+	_ = d.Writer.Do(nil, nil, func(_ *sql.Tx) error {
+		sp, err = d.Invites.DeleteInviteEvent(ctx, inviteEventID)
+		return nil
+	})
+	return
 }
 
 // GetAccountDataInRange returns all account data for a given user inserted or
@@ -207,7 +208,7 @@ func (d *Database) GetAccountDataInRange(
 func (d *Database) UpsertAccountData(
 	ctx context.Context, userID, roomID, dataType string,
 ) (sp types.StreamPosition, err error) {
-	err = sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
 		sp, err = d.AccountData.InsertAccountData(ctx, txn, userID, roomID, dataType)
 		return err
 	})
@@ -237,6 +238,7 @@ func (d *Database) StreamEventsToEvents(device *userapi.Device, in []types.Strea
 // handleBackwardExtremities adds this event as a backwards extremity if and only if we do not have all of
 // the events listed in the event's 'prev_events'. This function also updates the backwards extremities table
 // to account for the fact that the given event is no longer a backwards extremity, but may be marked as such.
+// This function should always be called within a sqlutil.Writer for safety in SQLite.
 func (d *Database) handleBackwardExtremities(ctx context.Context, txn *sql.Tx, ev *gomatrixserverlib.HeaderedEvent) error {
 	if err := d.BackwardExtremities.DeleteBackwardExtremity(ctx, txn, ev.RoomID(), ev.EventID()); err != nil {
 		return err
@@ -275,7 +277,7 @@ func (d *Database) WriteEvent(
 	addStateEventIDs, removeStateEventIDs []string,
 	transactionID *api.TransactionID, excludeFromSync bool,
 ) (pduPosition types.StreamPosition, returnErr error) {
-	returnErr = sqlutil.WithTransaction(d.DB, func(txn *sql.Tx) error {
+	returnErr = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
 		var err error
 		pos, err := d.OutputEvents.InsertEvent(
 			ctx, txn, ev, addStateEventIDs, removeStateEventIDs, transactionID, excludeFromSync,
@@ -304,6 +306,7 @@ func (d *Database) WriteEvent(
 	return pduPosition, returnErr
 }
 
+// This function should always be called within a sqlutil.Writer for safety in SQLite.
 func (d *Database) updateRoomState(
 	ctx context.Context, txn *sql.Tx,
 	removedEventIDs []string,
@@ -1114,7 +1117,7 @@ func (d *Database) StoreNewSendForDeviceMessage(
 	}
 	// Delegate the database write task to the SendToDeviceWriter. It'll guarantee
 	// that we don't lock the table for writes in more than one place.
-	err = d.SendToDeviceWriter.Do(d.DB, nil, func(txn *sql.Tx) error {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
 		return d.AddSendToDeviceEvent(
 			ctx, txn, userID, deviceID, string(j),
 		)
@@ -1179,7 +1182,7 @@ func (d *Database) CleanSendToDeviceUpdates(
 	// If we need to write to the database then we'll ask the SendToDeviceWriter to
 	// do that for us. It'll guarantee that we don't lock the table for writes in
 	// more than one place.
-	err = d.SendToDeviceWriter.Do(d.DB, nil, func(txn *sql.Tx) error {
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
 		// Delete any send-to-device messages marked for deletion.
 		if e := d.SendToDevice.DeleteSendToDeviceMessages(ctx, txn, toDelete); e != nil {
 			return fmt.Errorf("d.SendToDevice.DeleteSendToDeviceMessages: %w", e)

syncapi/storage/sqlite3/account_data_table.go

@@ -20,7 +20,6 @@ import (
 	"database/sql"
 
 	"github.com/matrix-org/dendrite/internal"
-	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/syncapi/storage/tables"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -51,7 +50,6 @@ const selectMaxAccountDataIDSQL = "" +
 
 type accountDataStatements struct {
 	db                           *sql.DB
-	writer                       sqlutil.TransactionWriter
 	streamIDStatements           *streamIDStatements
 	insertAccountDataStmt        *sql.Stmt
 	selectMaxAccountDataIDStmt   *sql.Stmt
@@ -61,7 +59,6 @@ type accountDataStatements struct {
 func NewSqliteAccountDataTable(db *sql.DB, streamID *streamIDStatements) (tables.AccountData, error) {
 	s := &accountDataStatements{
 		db:                 db,
-		writer:             sqlutil.NewTransactionWriter(),
 		streamIDStatements: streamID,
 	}
 	_, err := db.Exec(accountDataSchema)
@@ -84,15 +81,12 @@ func (s *accountDataStatements) InsertAccountData(
 	ctx context.Context, txn *sql.Tx,
 	userID, roomID, dataType string,
 ) (pos types.StreamPosition, err error) {
-	return pos, s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
-		var err error
 	pos, err = s.streamIDStatements.nextStreamID(ctx, txn)
 	if err != nil {
-			return err
+		return
 	}
 	_, err = txn.Stmt(s.insertAccountDataStmt).ExecContext(ctx, pos, userID, roomID, dataType)
-		return err
+	return
-	})
 }
 
 func (s *accountDataStatements) SelectAccountDataInRange(

syncapi/storage/sqlite3/backwards_extremities_table.go

@@ -19,7 +19,6 @@ import (
 	"database/sql"
 
 	"github.com/matrix-org/dendrite/internal"
-	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/syncapi/storage/tables"
 )
 
@@ -49,7 +48,6 @@ const deleteBackwardExtremitySQL = "" +
 
 type backwardExtremitiesStatements struct {
 	db                                   *sql.DB
-	writer                               sqlutil.TransactionWriter
 	insertBackwardExtremityStmt          *sql.Stmt
 	selectBackwardExtremitiesForRoomStmt *sql.Stmt
 	deleteBackwardExtremityStmt          *sql.Stmt
@@ -58,7 +56,6 @@ type backwardExtremitiesStatements struct {
 func NewSqliteBackwardsExtremitiesTable(db *sql.DB) (tables.BackwardsExtremities, error) {
 	s := &backwardExtremitiesStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err := db.Exec(backwardExtremitiesSchema)
 	if err != nil {
@@ -79,10 +76,8 @@ func NewSqliteBackwardsExtremitiesTable(db *sql.DB) (tables.BackwardsExtremities
 func (s *backwardExtremitiesStatements) InsertsBackwardExtremity(
 	ctx context.Context, txn *sql.Tx, roomID, eventID string, prevEventID string,
 ) (err error) {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+	_, err = txn.Stmt(s.insertBackwardExtremityStmt).ExecContext(ctx, roomID, eventID, prevEventID)
-		_, err := txn.Stmt(s.insertBackwardExtremityStmt).ExecContext(ctx, roomID, eventID, prevEventID)
 	return err
-	})
 }
 
 func (s *backwardExtremitiesStatements) SelectBackwardExtremitiesForRoom(
@@ -110,8 +105,6 @@ func (s *backwardExtremitiesStatements) SelectBackwardExtremitiesForRoom(
 func (s *backwardExtremitiesStatements) DeleteBackwardExtremity(
 	ctx context.Context, txn *sql.Tx, roomID, knownEventID string,
 ) (err error) {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+	_, err = txn.Stmt(s.deleteBackwardExtremityStmt).ExecContext(ctx, roomID, knownEventID)
-		_, err := txn.Stmt(s.deleteBackwardExtremityStmt).ExecContext(ctx, roomID, knownEventID)
 	return err
-	})
 }

syncapi/storage/sqlite3/current_room_state_table.go

@@ -85,7 +85,6 @@ const selectEventsWithEventIDsSQL = "" +
 
 type currentRoomStateStatements struct {
 	db                              *sql.DB
-	writer                          sqlutil.TransactionWriter
 	streamIDStatements              *streamIDStatements
 	upsertRoomStateStmt             *sql.Stmt
 	deleteRoomStateByEventIDStmt    *sql.Stmt
@@ -98,7 +97,6 @@ type currentRoomStateStatements struct {
 func NewSqliteCurrentRoomStateTable(db *sql.DB, streamID *streamIDStatements) (tables.CurrentRoomState, error) {
 	s := &currentRoomStateStatements{
 		db:                 db,
-		writer:             sqlutil.NewTransactionWriter(),
 		streamIDStatements: streamID,
 	}
 	_, err := db.Exec(currentRoomStateSchema)
@@ -200,11 +198,9 @@ func (s *currentRoomStateStatements) SelectCurrentState(
 func (s *currentRoomStateStatements) DeleteRoomStateByEventID(
 	ctx context.Context, txn *sql.Tx, eventID string,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.deleteRoomStateByEventIDStmt)
 	_, err := stmt.ExecContext(ctx, eventID)
 	return err
-	})
 }
 
 func (s *currentRoomStateStatements) UpsertRoomState(
@@ -225,9 +221,8 @@ func (s *currentRoomStateStatements) UpsertRoomState(
 	}
 
 	// upsert state event
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.upsertRoomStateStmt)
-		_, err := stmt.ExecContext(
+	_, err = stmt.ExecContext(
 		ctx,
 		event.RoomID(),
 		event.EventID(),
@@ -240,7 +235,6 @@ func (s *currentRoomStateStatements) UpsertRoomState(
 		addedAt,
 	)
 	return err
-	})
 }
 
 func minOfInts(a, b int) int {

syncapi/storage/sqlite3/filter_table.go

@@ -20,7 +20,6 @@ import (
 	"encoding/json"
 	"fmt"
 
-	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/syncapi/storage/tables"
 	"github.com/matrix-org/gomatrixserverlib"
 )
@@ -52,7 +51,6 @@ const insertFilterSQL = "" +
 
 type filterStatements struct {
 	db                          *sql.DB
-	writer                      sqlutil.TransactionWriter
 	selectFilterStmt            *sql.Stmt
 	selectFilterIDByContentStmt *sql.Stmt
 	insertFilterStmt            *sql.Stmt
@@ -65,7 +63,6 @@ func NewSqliteFilterTable(db *sql.DB) (tables.Filter, error) {
 	}
 	s := &filterStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	if s.selectFilterStmt, err = db.Prepare(selectFilterSQL); err != nil {
 		return nil, err
@@ -114,7 +111,6 @@ func (s *filterStatements) InsertFilter(
 		return "", err
 	}
 
-	err = s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
 	// Check if filter already exists in the database using its localpart and content
 	//
 	// This can result in a race condition when two clients try to insert the
@@ -123,24 +119,22 @@ func (s *filterStatements) InsertFilter(
 	err = s.selectFilterIDByContentStmt.QueryRowContext(ctx,
 		localpart, filterJSON).Scan(&existingFilterID)
 	if err != nil && err != sql.ErrNoRows {
-			return err
+		return "", err
 	}
 	// If it does, return the existing ID
 	if existingFilterID != "" {
-			return nil
+		return existingFilterID, nil
 	}
 
 	// Otherwise insert the filter and return the new ID
 	res, err := s.insertFilterStmt.ExecContext(ctx, filterJSON, localpart)
 	if err != nil {
-			return err
+		return "", err
 	}
 	rowid, err := res.LastInsertId()
 	if err != nil {
-			return err
+		return "", err
 	}
 	filterID = fmt.Sprintf("%d", rowid)
-		return nil
-	})
 	return
 }

syncapi/storage/sqlite3/invites_table.go

@@ -59,7 +59,6 @@ const selectMaxInviteIDSQL = "" +
 
 type inviteEventsStatements struct {
 	db                            *sql.DB
-	writer                        sqlutil.TransactionWriter
 	streamIDStatements            *streamIDStatements
 	insertInviteEventStmt         *sql.Stmt
 	selectInviteEventsInRangeStmt *sql.Stmt
@@ -70,7 +69,6 @@ type inviteEventsStatements struct {
 func NewSqliteInvitesTable(db *sql.DB, streamID *streamIDStatements) (tables.Invites, error) {
 	s := &inviteEventsStatements{
 		db:                 db,
-		writer:             sqlutil.NewTransactionWriter(),
 		streamIDStatements: streamID,
 	}
 	_, err := db.Exec(inviteEventsSchema)
@@ -95,20 +93,19 @@ func NewSqliteInvitesTable(db *sql.DB, streamID *streamIDStatements) (tables.Inv
 func (s *inviteEventsStatements) InsertInviteEvent(
 	ctx context.Context, txn *sql.Tx, inviteEvent gomatrixserverlib.HeaderedEvent,
 ) (streamPos types.StreamPosition, err error) {
-	err = s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
-		var err error
 	streamPos, err = s.streamIDStatements.nextStreamID(ctx, txn)
 	if err != nil {
-			return err
+		return
 	}
 
 	var headeredJSON []byte
 	headeredJSON, err = json.Marshal(inviteEvent)
 	if err != nil {
-			return err
+		return
 	}
 
-		_, err = txn.Stmt(s.insertInviteEventStmt).ExecContext(
+	stmt := sqlutil.TxStmt(txn, s.insertInviteEventStmt)
+	_, err = stmt.ExecContext(
 		ctx,
 		streamPos,
 		inviteEvent.RoomID(),
@@ -116,24 +113,17 @@ func (s *inviteEventsStatements) InsertInviteEvent(
 		*inviteEvent.StateKey(),
 		headeredJSON,
 	)
-		return err
-	})
 	return
 }
 
 func (s *inviteEventsStatements) DeleteInviteEvent(
 	ctx context.Context, inviteEventID string,
 ) (types.StreamPosition, error) {
-	var streamPos types.StreamPosition
+	streamPos, err := s.streamIDStatements.nextStreamID(ctx, nil)
-	err := s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
-		var err error
-		streamPos, err = s.streamIDStatements.nextStreamID(ctx, nil)
 	if err != nil {
-			return err
+		return streamPos, err
 	}
 	_, err = s.deleteInviteEventStmt.ExecContext(ctx, streamPos, inviteEventID)
-		return err
-	})
 	return streamPos, err
 }
 

syncapi/storage/sqlite3/output_room_events_table.go

@@ -105,7 +105,6 @@ const selectStateInRangeSQL = "" +
 
 type outputRoomEventsStatements struct {
 	db                            *sql.DB
-	writer                        sqlutil.TransactionWriter
 	streamIDStatements            *streamIDStatements
 	insertEventStmt               *sql.Stmt
 	selectEventsStmt              *sql.Stmt
@@ -120,7 +119,6 @@ type outputRoomEventsStatements struct {
 func NewSqliteEventsTable(db *sql.DB, streamID *streamIDStatements) (tables.Events, error) {
 	s := &outputRoomEventsStatements{
 		db:                 db,
-		writer:             sqlutil.NewTransactionWriter(),
 		streamIDStatements: streamID,
 	}
 	_, err := db.Exec(outputRoomEventsSchema)
@@ -159,10 +157,8 @@ func (s *outputRoomEventsStatements) UpdateEventJSON(ctx context.Context, event
 	if err != nil {
 		return err
 	}
-	return s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
 	_, err = s.updateEventJSONStmt.ExecContext(ctx, headeredJSON, event.EventID())
 	return err
-	})
 }
 
 // selectStateInRange returns the state events between the two given PDU stream positions, exclusive of oldPos, inclusive of newPos.
@@ -304,15 +300,12 @@ func (s *outputRoomEventsStatements) InsertEvent(
 		return 0, err
 	}
 
-	var streamPos types.StreamPosition
+	streamPos, err := s.streamIDStatements.nextStreamID(ctx, txn)
-	err = s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
-		streamPos, err = s.streamIDStatements.nextStreamID(ctx, txn)
 	if err != nil {
-			return err
+		return 0, err
 	}
-
 	insertStmt := sqlutil.TxStmt(txn, s.insertEventStmt)
-		_, ierr := insertStmt.ExecContext(
+	_, err = insertStmt.ExecContext(
 		ctx,
 		streamPos,
 		event.RoomID(),
@@ -328,8 +321,6 @@ func (s *outputRoomEventsStatements) InsertEvent(
 		excludeFromSync,
 		excludeFromSync,
 	)
-		return ierr
-	})
 	return streamPos, err
 }
 

syncapi/storage/sqlite3/output_room_events_topology_table.go

@@ -67,7 +67,6 @@ const selectMaxPositionInTopologySQL = "" +
 
 type outputRoomEventsTopologyStatements struct {
 	db                              *sql.DB
-	writer                          sqlutil.TransactionWriter
 	insertEventInTopologyStmt       *sql.Stmt
 	selectEventIDsInRangeASCStmt    *sql.Stmt
 	selectEventIDsInRangeDESCStmt   *sql.Stmt
@@ -78,7 +77,6 @@ type outputRoomEventsTopologyStatements struct {
 func NewSqliteTopologyTable(db *sql.DB) (tables.Topology, error) {
 	s := &outputRoomEventsTopologyStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err := db.Exec(outputRoomEventsTopologySchema)
 	if err != nil {
@@ -107,13 +105,11 @@ func NewSqliteTopologyTable(db *sql.DB) (tables.Topology, error) {
 func (s *outputRoomEventsTopologyStatements) InsertEventInTopology(
 	ctx context.Context, txn *sql.Tx, event *gomatrixserverlib.HeaderedEvent, pos types.StreamPosition,
 ) (err error) {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.insertEventInTopologyStmt)
-		_, err := stmt.ExecContext(
+	_, err = stmt.ExecContext(
 		ctx, event.EventID(), event.Depth(), event.RoomID(), pos,
 	)
-		return err
+	return
-	})
 }
 
 func (s *outputRoomEventsTopologyStatements) SelectEventIDsInRange(

syncapi/storage/sqlite3/send_to_device_table.go

@@ -73,7 +73,6 @@ const deleteSendToDeviceMessagesSQL = `
 
 type sendToDeviceStatements struct {
 	db                             *sql.DB
-	writer                         sqlutil.TransactionWriter
 	insertSendToDeviceMessageStmt  *sql.Stmt
 	selectSendToDeviceMessagesStmt *sql.Stmt
 	countSendToDeviceMessagesStmt  *sql.Stmt
@@ -82,7 +81,6 @@ type sendToDeviceStatements struct {
 func NewSqliteSendToDeviceTable(db *sql.DB) (tables.SendToDevice, error) {
 	s := &sendToDeviceStatements{
 		db: db,
-		writer: sqlutil.NewTransactionWriter(),
 	}
 	_, err := db.Exec(sendToDeviceSchema)
 	if err != nil {
@@ -103,10 +101,8 @@ func NewSqliteSendToDeviceTable(db *sql.DB) (tables.SendToDevice, error) {
 func (s *sendToDeviceStatements) InsertSendToDeviceMessage(
 	ctx context.Context, txn *sql.Tx, userID, deviceID, content string,
 ) (err error) {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+	_, err = sqlutil.TxStmt(txn, s.insertSendToDeviceMessageStmt).ExecContext(ctx, userID, deviceID, content)
-		_, err := sqlutil.TxStmt(txn, s.insertSendToDeviceMessageStmt).ExecContext(ctx, userID, deviceID, content)
+	return
-		return err
-	})
 }
 
 func (s *sendToDeviceStatements) CountSendToDeviceMessages(
@@ -163,10 +159,8 @@ func (s *sendToDeviceStatements) UpdateSentSendToDeviceMessages(
 	for k, v := range nids {
 		params[k+1] = v
 	}
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+	_, err = txn.ExecContext(ctx, query, params...)
-		_, err := txn.ExecContext(ctx, query, params...)
+	return
-		return err
-	})
 }
 
 func (s *sendToDeviceStatements) DeleteSendToDeviceMessages(
@@ -177,8 +171,6 @@ func (s *sendToDeviceStatements) DeleteSendToDeviceMessages(
 	for k, v := range nids {
 		params[k] = v
 	}
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
+	_, err = txn.ExecContext(ctx, query, params...)
-		_, err := txn.ExecContext(ctx, query, params...)
+	return
-		return err
-	})
 }

syncapi/storage/sqlite3/stream_id_table.go

@@ -28,14 +28,12 @@ const selectStreamIDStmt = "" +
 
 type streamIDStatements struct {
 	db                   *sql.DB
-	writer               sqlutil.TransactionWriter
 	increaseStreamIDStmt *sql.Stmt
 	selectStreamIDStmt   *sql.Stmt
 }
 
 func (s *streamIDStatements) prepare(db *sql.DB) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
 	_, err = db.Exec(streamIDTableSchema)
 	if err != nil {
 		return
@@ -52,14 +50,9 @@ func (s *streamIDStatements) prepare(db *sql.DB) (err error) {
 func (s *streamIDStatements) nextStreamID(ctx context.Context, txn *sql.Tx) (pos types.StreamPosition, err error) {
 	increaseStmt := sqlutil.TxStmt(txn, s.increaseStreamIDStmt)
 	selectStmt := sqlutil.TxStmt(txn, s.selectStreamIDStmt)
-	err = s.writer.Do(s.db, nil, func(txn *sql.Tx) error {
+	if _, err = increaseStmt.ExecContext(ctx, "global"); err != nil {
-		if _, ierr := increaseStmt.ExecContext(ctx, "global"); err != nil {
+		return
-			return ierr
 	}
-		if serr := selectStmt.QueryRowContext(ctx, "global").Scan(&pos); err != nil {
+	err = selectStmt.QueryRowContext(ctx, "global").Scan(&pos)
-			return serr
-		}
-		return nil
-	})
 	return
 }

syncapi/storage/sqlite3/syncserver.go

@@ -32,6 +32,7 @@ import (
 type SyncServerDatasource struct {
 	shared.Database
 	db     *sql.DB
+	writer sqlutil.Writer
 	sqlutil.PartitionOffsetStatements
 	streamID streamIDStatements
 }
@@ -44,6 +45,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*SyncServerDatasource, e
 	if d.db, err = sqlutil.Open(dbProperties); err != nil {
 		return nil, err
 	}
+	d.writer = sqlutil.NewExclusiveWriter()
 	if err = d.prepare(); err != nil {
 		return nil, err
 	}
@@ -51,7 +53,7 @@ func NewDatabase(dbProperties *config.DatabaseOptions) (*SyncServerDatasource, e
 }
 
 func (d *SyncServerDatasource) prepare() (err error) {
-	if err = d.PartitionOffsetStatements.Prepare(d.db, "syncapi"); err != nil {
+	if err = d.PartitionOffsetStatements.Prepare(d.db, d.writer, "syncapi"); err != nil {
 		return err
 	}
 	if err = d.streamID.prepare(d.db); err != nil {
@@ -91,6 +93,7 @@ func (d *SyncServerDatasource) prepare() (err error) {
 	}
 	d.Database = shared.Database{
 		DB:                  d.db,
+		Writer:              sqlutil.NewExclusiveWriter(),
 		Invites:             invites,
 		AccountData:         accountData,
 		OutputEvents:        events,
@@ -99,7 +102,6 @@ func (d *SyncServerDatasource) prepare() (err error) {
 		Topology:            topology,
 		Filter:              filter,
 		SendToDevice:        sendToDevice,
-		SendToDeviceWriter:  sqlutil.NewTransactionWriter(),
 		EDUCache:            cache.New(),
 	}
 	return nil

userapi/storage/accounts/postgres/storage.go

@@ -35,6 +35,7 @@ import (
 // Database represents an account database
 type Database struct {
 	db     *sql.DB
+	writer sqlutil.Writer
 	sqlutil.PartitionOffsetStatements
 	accounts     accountsStatements
 	profiles     profilesStatements
@@ -49,27 +50,27 @@ func NewDatabase(dbProperties *config.DatabaseOptions, serverName gomatrixserver
 	if err != nil {
 		return nil, err
 	}
-	partitions := sqlutil.PartitionOffsetStatements{}
+	d := &Database{
-	if err = partitions.Prepare(db, "account"); err != nil {
+		serverName: serverName,
+		db:         db,
+		writer:     sqlutil.NewDummyWriter(),
+	}
+	if err = d.PartitionOffsetStatements.Prepare(db, d.writer, "account"); err != nil {
 		return nil, err
 	}
-	a := accountsStatements{}
+	if err = d.accounts.prepare(db, serverName); err != nil {
-	if err = a.prepare(db, serverName); err != nil {
 		return nil, err
 	}
-	p := profilesStatements{}
+	if err = d.profiles.prepare(db); err != nil {
-	if err = p.prepare(db); err != nil {
 		return nil, err
 	}
-	ac := accountDataStatements{}
+	if err = d.accountDatas.prepare(db); err != nil {
-	if err = ac.prepare(db); err != nil {
 		return nil, err
 	}
-	t := threepidStatements{}
+	if err = d.threepids.prepare(db); err != nil {
-	if err = t.prepare(db); err != nil {
 		return nil, err
 	}
-	return &Database{db, partitions, a, p, ac, t, serverName}, nil
+	return d, nil
 }
 
 // GetAccountByPassword returns the account associated with the given localpart and password.

userapi/storage/accounts/sqlite3/account_data_table.go

@@ -51,15 +51,15 @@ const selectAccountDataByTypeSQL = "" +
 
 type accountDataStatements struct {
 	db                          *sql.DB
-	writer                      sqlutil.TransactionWriter
+	writer                      sqlutil.Writer
 	insertAccountDataStmt       *sql.Stmt
 	selectAccountDataStmt       *sql.Stmt
 	selectAccountDataByTypeStmt *sql.Stmt
 }
 
-func (s *accountDataStatements) prepare(db *sql.DB) (err error) {
+func (s *accountDataStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 	_, err = db.Exec(accountDataSchema)
 	if err != nil {
 		return

userapi/storage/accounts/sqlite3/accounts_table.go

@@ -59,7 +59,7 @@ const selectNewNumericLocalpartSQL = "" +
 
 type accountsStatements struct {
 	db                            *sql.DB
-	writer                        sqlutil.TransactionWriter
+	writer                        sqlutil.Writer
 	insertAccountStmt             *sql.Stmt
 	selectAccountByLocalpartStmt  *sql.Stmt
 	selectPasswordHashStmt        *sql.Stmt
@@ -67,9 +67,9 @@ type accountsStatements struct {
 	serverName                    gomatrixserverlib.ServerName
 }
 
-func (s *accountsStatements) prepare(db *sql.DB, server gomatrixserverlib.ServerName) (err error) {
+func (s *accountsStatements) prepare(db *sql.DB, writer sqlutil.Writer, server gomatrixserverlib.ServerName) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 	_, err = db.Exec(accountsSchema)
 	if err != nil {
 		return

userapi/storage/accounts/sqlite3/profile_table.go

@@ -53,7 +53,7 @@ const selectProfilesBySearchSQL = "" +
 
 type profilesStatements struct {
 	db                           *sql.DB
-	writer                       sqlutil.TransactionWriter
+	writer                       sqlutil.Writer
 	insertProfileStmt            *sql.Stmt
 	selectProfileByLocalpartStmt *sql.Stmt
 	setAvatarURLStmt             *sql.Stmt
@@ -61,9 +61,9 @@ type profilesStatements struct {
 	selectProfilesBySearchStmt   *sql.Stmt
 }
 
-func (s *profilesStatements) prepare(db *sql.DB) (err error) {
+func (s *profilesStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 	_, err = db.Exec(profilesSchema)
 	if err != nil {
 		return

userapi/storage/accounts/sqlite3/storage.go

@@ -34,6 +34,8 @@ import (
 // Database represents an account database
 type Database struct {
 	db     *sql.DB
+	writer sqlutil.Writer
+
 	sqlutil.PartitionOffsetStatements
 	accounts     accountsStatements
 	profiles     profilesStatements
@@ -53,35 +55,28 @@ func NewDatabase(dbProperties *config.DatabaseOptions, serverName gomatrixserver
 	if err != nil {
 		return nil, err
 	}
-	partitions := sqlutil.PartitionOffsetStatements{}
+	d := &Database{
-	if err = partitions.Prepare(db, "account"); err != nil {
-		return nil, err
-	}
-	a := accountsStatements{}
-	if err = a.prepare(db, serverName); err != nil {
-		return nil, err
-	}
-	p := profilesStatements{}
-	if err = p.prepare(db); err != nil {
-		return nil, err
-	}
-	ac := accountDataStatements{}
-	if err = ac.prepare(db); err != nil {
-		return nil, err
-	}
-	t := threepidStatements{}
-	if err = t.prepare(db); err != nil {
-		return nil, err
-	}
-	return &Database{
-		db:                        db,
-		PartitionOffsetStatements: partitions,
-		accounts:                  a,
-		profiles:                  p,
-		accountDatas:              ac,
-		threepids:                 t,
 		serverName: serverName,
-	}, nil
+		db:         db,
+		writer:     sqlutil.NewExclusiveWriter(),
+	}
+	partitions := sqlutil.PartitionOffsetStatements{}
+	if err = partitions.Prepare(db, d.writer, "account"); err != nil {
+		return nil, err
+	}
+	if err = d.accounts.prepare(db, d.writer, serverName); err != nil {
+		return nil, err
+	}
+	if err = d.profiles.prepare(db, d.writer); err != nil {
+		return nil, err
+	}
+	if err = d.accountDatas.prepare(db, d.writer); err != nil {
+		return nil, err
+	}
+	if err = d.threepids.prepare(db, d.writer); err != nil {
+		return nil, err
+	}
+	return d, nil
 }
 
 // GetAccountByPassword returns the account associated with the given localpart and password.

userapi/storage/accounts/sqlite3/threepid_table.go

@@ -54,16 +54,16 @@ const deleteThreePIDSQL = "" +
 
 type threepidStatements struct {
 	db                              *sql.DB
-	writer                          sqlutil.TransactionWriter
+	writer                          sqlutil.Writer
 	selectLocalpartForThreePIDStmt  *sql.Stmt
 	selectThreePIDsForLocalpartStmt *sql.Stmt
 	insertThreePIDStmt              *sql.Stmt
 	deleteThreePIDStmt              *sql.Stmt
 }
 
-func (s *threepidStatements) prepare(db *sql.DB) (err error) {
+func (s *threepidStatements) prepare(db *sql.DB, writer sqlutil.Writer) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 	_, err = db.Exec(threepidSchema)
 	if err != nil {
 		return

userapi/storage/devices/sqlite3/devices_table.go

@@ -78,7 +78,7 @@ const selectDevicesByIDSQL = "" +
 
 type devicesStatements struct {
 	db                           *sql.DB
-	writer                       sqlutil.TransactionWriter
+	writer                       sqlutil.Writer
 	insertDeviceStmt             *sql.Stmt
 	selectDevicesCountStmt       *sql.Stmt
 	selectDeviceByTokenStmt      *sql.Stmt
@@ -91,9 +91,9 @@ type devicesStatements struct {
 	serverName                   gomatrixserverlib.ServerName
 }
 
-func (s *devicesStatements) prepare(db *sql.DB, server gomatrixserverlib.ServerName) (err error) {
+func (s *devicesStatements) prepare(db *sql.DB, writer sqlutil.Writer, server gomatrixserverlib.ServerName) (err error) {
 	s.db = db
-	s.writer = sqlutil.NewTransactionWriter()
+	s.writer = writer
 	_, err = db.Exec(devicesSchema)
 	if err != nil {
 		return
@@ -138,19 +138,13 @@ func (s *devicesStatements) insertDevice(
 ) (*api.Device, error) {
 	createdTimeMS := time.Now().UnixNano() / 1000000
 	var sessionID int64
-	err := s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	countStmt := sqlutil.TxStmt(txn, s.selectDevicesCountStmt)
 	insertStmt := sqlutil.TxStmt(txn, s.insertDeviceStmt)
 	if err := countStmt.QueryRowContext(ctx).Scan(&sessionID); err != nil {
-			return err
+		return nil, err
 	}
 	sessionID++
 	if _, err := insertStmt.ExecContext(ctx, id, localpart, accessToken, createdTimeMS, displayName, sessionID); err != nil {
-			return err
-		}
-		return nil
-	})
-	if err != nil {
 		return nil, err
 	}
 	return &api.Device{
@@ -164,11 +158,9 @@ func (s *devicesStatements) insertDevice(
 func (s *devicesStatements) deleteDevice(
 	ctx context.Context, txn *sql.Tx, id, localpart string,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.deleteDeviceStmt)
 	_, err := stmt.ExecContext(ctx, id, localpart)
 	return err
-	})
 }
 
 func (s *devicesStatements) deleteDevices(
@@ -179,7 +171,6 @@ func (s *devicesStatements) deleteDevices(
 	if err != nil {
 		return err
 	}
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, prep)
 	params := make([]interface{}, len(devices)+1)
 	params[0] = localpart
@@ -188,27 +179,22 @@ func (s *devicesStatements) deleteDevices(
 	}
 	_, err = stmt.ExecContext(ctx, params...)
 	return err
-	})
 }
 
 func (s *devicesStatements) deleteDevicesByLocalpart(
 	ctx context.Context, txn *sql.Tx, localpart string,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.deleteDevicesByLocalpartStmt)
 	_, err := stmt.ExecContext(ctx, localpart)
 	return err
-	})
 }
 
 func (s *devicesStatements) updateDeviceName(
 	ctx context.Context, txn *sql.Tx, localpart, deviceID string, displayName *string,
 ) error {
-	return s.writer.Do(s.db, txn, func(txn *sql.Tx) error {
 	stmt := sqlutil.TxStmt(txn, s.updateDeviceNameStmt)
 	_, err := stmt.ExecContext(ctx, displayName, localpart, deviceID)
 	return err
-	})
 }
 
 func (s *devicesStatements) selectDeviceByToken(

userapi/storage/devices/sqlite3/storage.go

@@ -34,6 +34,7 @@ var deviceIDByteLength = 6
 // Database represents a device database.
 type Database struct {
 	db      *sql.DB
+	writer  sqlutil.Writer
 	devices devicesStatements
 }
 
@@ -43,11 +44,12 @@ func NewDatabase(dbProperties *config.DatabaseOptions, serverName gomatrixserver
 	if err != nil {
 		return nil, err
 	}
+	writer := sqlutil.NewExclusiveWriter()
 	d := devicesStatements{}
-	if err = d.prepare(db, serverName); err != nil {
+	if err = d.prepare(db, writer, serverName); err != nil {
 		return nil, err
 	}
-	return &Database{db, d}, nil
+	return &Database{db, writer, d}, nil
 }
 
 // GetDeviceByAccessToken returns the device matching the given access token.
@@ -88,7 +90,7 @@ func (d *Database) CreateDevice(
 	displayName *string,
 ) (dev *api.Device, returnErr error) {
 	if deviceID != nil {
-		returnErr = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
+		returnErr = d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
 			var err error
 			// Revoke existing tokens for this device
 			if err = d.devices.deleteDevice(ctx, txn, *deviceID, localpart); err != nil {
@@ -108,7 +110,7 @@ func (d *Database) CreateDevice(
 				return
 			}
 
-			returnErr = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
+			returnErr = d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
 				var err error
 				dev, err = d.devices.insertDevice(ctx, txn, newDeviceID, localpart, accessToken, displayName)
 				return err
@@ -138,7 +140,7 @@ func generateDeviceID() (string, error) {
 func (d *Database) UpdateDevice(
 	ctx context.Context, localpart, deviceID string, displayName *string,
 ) error {
-	return sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
+	return d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
 		return d.devices.updateDeviceName(ctx, txn, localpart, deviceID, displayName)
 	})
 }
@@ -150,7 +152,7 @@ func (d *Database) UpdateDevice(
 func (d *Database) RemoveDevice(
 	ctx context.Context, deviceID, localpart string,
 ) error {
-	return sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
+	return d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
 		if err := d.devices.deleteDevice(ctx, txn, deviceID, localpart); err != sql.ErrNoRows {
 			return err
 		}
@@ -165,7 +167,7 @@ func (d *Database) RemoveDevice(
 func (d *Database) RemoveDevices(
 	ctx context.Context, localpart string, devices []string,
 ) error {
-	return sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
+	return d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
 		if err := d.devices.deleteDevices(ctx, txn, localpart, devices); err != sql.ErrNoRows {
 			return err
 		}
@@ -179,7 +181,7 @@ func (d *Database) RemoveDevices(
 func (d *Database) RemoveAllDevices(
 	ctx context.Context, localpart string,
 ) error {
-	return sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
+	return d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
 		if err := d.devices.deleteDevicesByLocalpart(ctx, txn, localpart); err != sql.ErrNoRows {
 			return err
 		}