[release-20.0] Online DDL: fix defer function, potential connection pool exhaustion (#17207)

go/vt/vttablet/onlineddl/executor.go

@@ -964,9 +964,22 @@
 
 	lockConn, err := e.pool.Get(ctx, nil)
 	if err != nil {
+<<<<<<< HEAD
 		return err
 	}
 	defer lockConn.Recycle()
+=======
+		return vterrors.Wrapf(err, "failed getting locking connection")
+	}
+	defer lockConn.Recycle()
+	// Set large enough `@@lock_wait_timeout` so that it does not interfere with the cut-over operation.
+	// The code will ensure everything that needs to be terminated by `migrationCutOverThreshold` will be terminated.
+	lockConnRestoreLockWaitTimeout, err := e.initConnectionLockWaitTimeout(ctx, lockConn.Conn, 5*migrationCutOverThreshold)
+	if err != nil {
+		return vterrors.Wrapf(err, "failed setting lock_wait_timeout on locking connection")
+	}
+	defer lockConnRestoreLockWaitTimeout()
+>>>>>>> 8952b5af4e (Online DDL: fix defer function, potential connection pool exhaustion (#17207))
 	defer lockConn.Conn.Exec(ctx, sqlUnlockTables, 1, false)
 
 	renameCompleteChan := make(chan error)
@@ -976,14 +989,14 @@
 		return err
 	}
 	defer renameConn.Recycle()
 	defer func() {
 		if !renameWasSuccessful {
 			err := renameConn.Conn.Kill("premature exit while renaming tables", 0)
 			if err != nil {
 				log.Warningf("Failed to kill connection being used to rename tables in OnlineDDL migration %s: %v", onlineDDL.UUID, err)
 			}
 		}
 	}()
 	// See if backend MySQL server supports 'rename_table_preserve_foreign_key' variable
 	preserveFKSupported, err := e.isPreserveForeignKeySupported(ctx)
 	if err != nil {
@@ -1000,12 +1013,12 @@
 	}
 
 	renameQuery := sqlparser.BuildParsedQuery(sqlSwapTables, onlineDDL.Table, sentryTableName, vreplTable, onlineDDL.Table, sentryTableName, vreplTable)
 	waitForRenameProcess := func() error {
 		// This function waits until it finds the RENAME TABLE... query running in MySQL's PROCESSLIST, or until timeout
 		// The function assumes that one of the renamed tables is locked, thus causing the RENAME to block. If nothing
 		// is locked, then the RENAME will be near-instantaneous and it's unlikely that the function will find it.
 		renameWaitCtx, cancel := context.WithTimeout(ctx, migrationCutOverThreshold)
 		defer cancel()
 
 		for {
 			renameProcessFound, err := e.doesConnectionInfoMatch(renameWaitCtx, renameConn.Conn.ID(), "rename")