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RESTART REQUESTS

According to the Firebird sources, this will

Restart all requests in the current attachment to utilize the passed transaction.

— src/jrd/tra.cpp

The exact semantics and effects of this clause are not clear, and we recommend you do not use this clause.

AUTO COMMIT

Specifying AUTO COMMIT enables auto-commit mode for the transaction.In auto-commit mode, Firebird will internally execute the equivalent of COMMIT RETAIN after each statement execution.

Caution

This is not a generally useful auto-commit mode;the same transaction context is retained until the transaction is ended through a commit or rollback.In other words, when you use SNAPSHOT or SNAPSHOT TABLE STABILITY, this auto-commit will not change record visibility (effects of transactions that were committed after this transaction was started will not be visible).

For READ COMMITTED, the same warnings apply as for commit retaining: prolonged use of a single transaction in auto-commit mode can inhibit garbage collection and degrade performance.
IGNORE LIMBO

This flag is used to signal that records created by limbo transactions are to be ignored.Transactions are left “in limbo” if the second stage of a two-phase commit fails.

Note
Historical Note

IGNORE LIMBO surfaces the TPB parameter isc_tpb_ignore_limbo, available in the API since InterBase times and is mainly used by gfix.
RESERVING

The RESERVING clause in the SET TRANSACTION statement reserves tables specified in the table list.Reserving a table prevents other transactions from making changes in them or even, with the inclusion of certain parameters, from reading data from them while this transaction is running.

A RESERVING clause can also be used to specify a list of tables that can be changed by other transactions, even if the transaction is started with the SNAPSHOT TABLE STABILITY isolation level.

One RESERVING clause is used to specify as many reserved tables as required.