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SAVEPOINT

Creates a savepoint

Syntax
SAVEPOINT sp_name
Table 1. SAVEPOINT Statement Parameter
Parameter Description

sp_name

Savepoint name.Available only in DSQL

The SAVEPOINT statement creates an SQL-compliant savepoint that acts as a marker in the “stack” of data activities within a transaction.Subsequently, the tasks performed in the “stack” can be undone back to this savepoint, leaving the earlier work and older savepoints untouched.Savepoints are sometimes called “nested transactions”.

If a savepoint already exists with the same name as the name supplied for the new one, the existing savepoint is released, and a new one is created using the supplied name.

To roll changes back to the savepoint, the statement ROLLBACK TO SAVEPOINT is used.

Note
Memory Considerations

The internal mechanism beneath savepoints can consume large amounts of memory, especially if the same rows receive multiple updates in one transaction.When a savepoint is no longer needed, but the transaction still has work to do, a [fblangref50-transacs-releasesp] statement will erase it and thus free the resources.
Sample DSQL session with savepoints
CREATE TABLE TEST (ID INTEGER);
COMMIT;
INSERT INTO TEST VALUES (1);
COMMIT;
INSERT INTO TEST VALUES (2);
SAVEPOINT Y;
DELETE FROM TEST;
SELECT * FROM TEST; -- returns no rows
ROLLBACK TO Y;
SELECT * FROM TEST; -- returns two rows
ROLLBACK;
SELECT * FROM TEST; -- returns one row
See also

[fblangref50-transacs-rollback-tosavepoint], [fblangref50-transacs-releasesp]

RELEASE SAVEPOINT

Releases a savepoint

Syntax
RELEASE SAVEPOINT sp_name [ONLY]
Table 1. RELEASE SAVEPOINT Statement Parameter
Parameter Description

sp_name

Savepoint name.Available only in DSQL

The statement RELEASE SAVEPOINT erases a named savepoint, freeing up all the resources it encompasses.By default, all the savepoints created after the named savepoint are released as well.The qualifier ONLY directs the engine to release only the named savepoint.

See also

[fblangref50-transacs-savepoint]

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Internal Savepoints

By default, the engine uses an automatic transaction-level system savepoint to perform transaction rollback.When a ROLLBACK statement is issued, all changes performed in this transaction are backed out via a transaction-level savepoint, and the transaction is then committed.This logic reduces the amount of garbage collection caused by rolled back transactions.

When the volume of changes performed under a transaction-level savepoint is getting large (~50000 records affected), the engine releases the transaction-level savepoint and uses the Transaction Inventory Page (TIP) as a mechanism to roll back the transaction if needed.

Tip

If you expect the volume of changes in your transaction to be large, you can specify the NO AUTO UNDO option in your SET TRANSACTION statement to block the creation of the transaction-level savepoint.Using the API, you can set this with the TPB flag isc_tpb_no_auto_undo.

Savepoints and PSQL

Transaction control statements are not allowed in PSQL, as that would break the atomicity of the statement that calls the procedure.However, Firebird does support the raising and handling of exceptions in PSQL, so that actions performed in stored procedures and triggers can be selectively undone without the entire procedure failing.

Internally, automatic savepoints are used to:

  • undo all actions in the BEGIN…​END block where an exception occurs

  • undo all actions performed by the procedure or trigger or, in a selectable procedure, all actions performed since the last SUSPEND, when execution terminates prematurely because of an uncaught error or exception

Each PSQL exception handling block is also bounded by automatic system savepoints.

Note

A BEGIN…​END block does not itself create an automatic savepoint.A savepoint is created only in blocks that contain the WHEN statement for handling exceptions.