MySQL driver: on connect try setting wsrep_sync_wait=4, swallow error…

… 1193

In Galera clusters wsrep_sync_wait=4 ensures inserted rows to be synced over
all nodes before reporting success to their inserter. That allows inserting
child rows immediately after that on another node without running into
foreign key errors. MySQL single nodes will reject this with error 1193
"Unknown system variable" which is OK.

pkg/driver/driver.go

@@ -32,7 +32,13 @@ func (c RetryConnector) Connect(ctx context.Context) (driver.Conn, error) {
 	err := errors.Wrap(retry.WithBackoff(
 		ctx,
 		func(ctx context.Context) (err error) {
-			conn, err = c.Connector.Connect(ctx)
+			if conn, err = c.Connector.Connect(ctx); err == nil && c.driver.initConn != nil {
+				if err = c.driver.initConn(conn); err != nil {
+					_ = conn.Close()
+					conn = nil
+				}
+			}
+
 			return
 		},
 		shouldRetry,
@@ -67,7 +73,9 @@ func (c RetryConnector) Driver() driver.Driver {
 // Driver wraps a driver.Driver that also must implement driver.DriverContext with logging capabilities and provides our RetryConnector.
 type Driver struct {
 	ctxDriver
-	Logger *logging.Logger
+
+	Logger   *logging.Logger
+	initConn func(driver.Conn) error
 }
 
 // OpenConnector implements the DriverContext interface.
@@ -85,7 +93,7 @@ func (d Driver) OpenConnector(name string) (driver.Connector, error) {
 
 // Register makes our database Driver available under the name "icingadb-*sql".
 func Register(logger *logging.Logger) {
-	sql.Register(MySQL, &Driver{ctxDriver: &mysql.MySQLDriver{}, Logger: logger})
+	sql.Register(MySQL, &Driver{ctxDriver: &mysql.MySQLDriver{}, Logger: logger, initConn: setGaleraOpts})
 	sql.Register(PostgreSQL, &Driver{ctxDriver: PgSQLDriver{}, Logger: logger})
 	_ = mysql.SetLogger(mysqlLogger(func(v ...interface{}) { logger.Debug(v...) }))
 	sqlx.BindDriver(PostgreSQL, sqlx.DOLLAR)

pkg/driver/mysql.go

@@ -0,0 +1,33 @@
+package driver
+
+import (
+	"database/sql/driver"
+	"github.com/go-sql-driver/mysql"
+	"github.com/pkg/errors"
+)
+
+// setGaleraOpts tries SET SESSION wsrep_sync_wait=4.
+// Error 1193 "Unknown system variable" is ignored to support MySQL single nodes.
+func setGaleraOpts(conn driver.Conn) error {
+	const galeraOpts = "SET SESSION wsrep_sync_wait=4"
+
+	stmt, err := conn.Prepare(galeraOpts)
+	if err != nil {
+		err = errors.Wrap(err, "can't prepare "+galeraOpts)
+		//lint:ignore SA1019 StmtExecContext isn't mandatory, would fall back anyway
+	} else if _, err = stmt.Exec(nil); err != nil {
+		err = errors.Wrap(err, "can't execute "+galeraOpts)
+		_ = stmt.Close()
+	} else if err = stmt.Close(); err != nil {
+		err = errors.Wrap(err, "can't close statement "+galeraOpts)
+	}
+
+	if err != nil {
+		var me *mysql.MySQLError
+		if errors.As(err, &me) && me.Number == 1193 {
+			err = nil
+		}
+	}
+
+	return err
+}