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

@@ -85,7 +85,7 @@ 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: &mySQLDriver{}, Logger: logger})
 	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 +1,84 @@
+package driver
+
+import (
+	"context"
+	"database/sql/driver"
+	"github.com/go-sql-driver/mysql"
+	"github.com/pkg/errors"
+)
+
+// mySQLDriver extends mysql.MySQLDriver with auto-SETting Galera cluster options.
+type mySQLDriver struct {
+	mysql.MySQLDriver
+}
+
+// Open implements the driver.Driver interface.
+func (md mySQLDriver) Open(name string) (driver.Conn, error) {
+	return setGaleraOpts(md.MySQLDriver.Open(name))
+}
+
+// OpenConnector implements the driver.DriverContext interface.
+func (md mySQLDriver) OpenConnector(name string) (driver.Connector, error) {
+	connector, err := md.MySQLDriver.OpenConnector(name)
+	if err != nil {
+		return nil, err
+	}
+
+	return &galeraAwareConnector{connector, md}, nil
+}
+
+// galeraAwareConnector extends mysql.connector with auto-SETting Galera cluster options.
+type galeraAwareConnector struct {
+	driver.Connector
+
+	driver driver.Driver
+}
+
+// Connect implements the driver.Connector interface.
+func (gac *galeraAwareConnector) Connect(ctx context.Context) (driver.Conn, error) {
+	return setGaleraOpts(gac.Connector.Connect(ctx))
+}
+
+// Driver implements the driver.Connector interface.
+func (gac *galeraAwareConnector) Driver() driver.Driver {
+	return gac.driver
+}
+
+// setGaleraOpts tries SET SESSION wsrep_sync_wait=4 on conn if err != nil.
+// It closes conn on failure (as mysql.mysqlConn#handleParams() does).
+// Error 1193 "Unknown system variable" is ignored to support MySQL single nodes.
+func setGaleraOpts(conn driver.Conn, err error) (driver.Conn, error) {
+	const galeraOpts = "SET SESSION wsrep_sync_wait=4"
+
+	if err == nil {
+		var stmt driver.Stmt
+		if stmt, err = conn.Prepare(galeraOpts); 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 { // Unknown system variable
+				err = nil
+			} else {
+				_ = conn.Close()
+				conn = nil
+			}
+		}
+	}
+
+	return conn, err
+}
+
+// Assert interface compliance.
+var (
+	_ driver.Driver        = mySQLDriver{}
+	_ driver.DriverContext = mySQLDriver{}
+	_ driver.Connector     = (*galeraAwareConnector)(nil)
+)