TCL statements

This topic describes the TCL statements supported by PolarDB-X and the usage of these statements.

A database transaction is a single logical unit of work that consists of a collection of operations. You can perform transactions to maintain the data integrity of databases. This ensures that SQL operations in a batch are all executed or are not executed.

By default, PolarDB-X runs in autocommit mode. If the autocommit mode is enabled, each SQL statement forms a single transaction. The distributed transaction feature is disabled for DML statements that are executed across shards. The feature is enabled only for DML statements that update global secondary indexes, broadcast tables, and shard keys. This ensures high performance. You can manually start an interactive transaction that consists of multiple statements by executing the SET AUTOCOMMIT=0 statement or specifying the transaction name.

An explicit transaction is a user-defined or user-specified transaction. An explicit transaction is a transaction that starts with the START TRANSACTION or BEGIN statement and ends with the COMMIT or ROLLBACK statement. BEGIN can be used as an alias of the START TRANSACTION statement.

Syntax

START TRANSACTION
  [transaction_characteristic [, transaction_characteristic] ...]

transaction_characteristic: {
    WITH CONSISTENT SNAPSHOT
   ISOLATION LEVEL {REPEATABLE READ  READ COMMITTED}
   READ WRITE
   READ ONLY
}

BEGIN
COMMIT
ROLLBACK
SET autocommit = {0  1}

The following table describes the parameters in the preceding statement.

{#concept-2118278-entry-6yy-1hq-gw0}