45.8. Transaction Management
Prev | Up | Chapter 45. PL/pgSQL — SQL Procedural Language | Home | Next

## 45.8. Transaction Management

In procedures invoked by the `CALL` command as well as in anonymous code blocks (`DO` command), it is possible to end transactions using the commands `COMMIT` and `ROLLBACK`. A new transaction is started automatically after a transaction is ended using these commands, so there is no separate `START TRANSACTION` command. (Note that `BEGIN` and `END` have different meanings in PL/pgSQL.)

Here is a simple example:

    CREATE PROCEDURE transaction_test1()
    LANGUAGE plpgsql
    AS $$
    BEGIN
        FOR i IN 0..9 LOOP
            INSERT INTO test1 (a) VALUES (i);
            IF i % 2 = 0 THEN
                COMMIT;
            ELSE
                ROLLBACK;
            END IF;
        END LOOP;
    END;
    $$;

    CALL transaction_test1();

A new transaction starts out with default transaction characteristics such as transaction isolation level. In cases where transactions are committed in a loop, it might be desirable to start new transactions automatically with the same characteristics as the previous one. The commands `COMMIT AND CHAIN` and `ROLLBACK AND CHAIN` accomplish this.

Transaction control is only possible in `CALL` or `DO` invocations from the top level or nested `CALL` or `DO` invocations without any other intervening command. For example, if the call stack is `CALL proc1()` → `CALL proc2()` → `CALL proc3()`, then the second and third procedures can perform transaction control actions. But if the call stack is `CALL proc1()` → `SELECT func2()` → `CALL proc3()`, then the last procedure cannot do transaction control, because of the `SELECT` in between.

Special considerations apply to cursor loops. Consider this example:

    CREATE PROCEDURE transaction_test2()
    LANGUAGE plpgsql
    AS $$
    DECLARE
        r RECORD;
    BEGIN
        FOR r IN SELECT * FROM test2 ORDER BY x LOOP
            INSERT INTO test1 (a) VALUES (r.x);
            COMMIT;
        END LOOP;
    END;
    $$;

    CALL transaction_test2();

Normally, cursors are automatically closed at transaction commit. However, a cursor created as part of a loop like this is automatically converted to a holdable cursor by the first `COMMIT` or `ROLLBACK`. That means that the cursor is fully evaluated at the first `COMMIT` or `ROLLBACK` rather than row by row. The cursor is still removed automatically after the loop, so this is mostly invisible to the user.

Transaction commands are not allowed in cursor loops driven by commands that are not read-only (for example `UPDATE ... RETURNING`).

A transaction cannot be ended inside a block with exception handlers.

Prev | Up | Next
45.7. Cursors | Home | 45.9. Errors and Messages