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.