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WAIT Mode

In the WAIT mode (the default mode), if a conflict occurs between two parallel processes executing concurrent data updates in the same database, a WAIT transaction will wait till the other transaction has finished — by committing (COMMIT) or rolling back (ROLLBACK).The client application with the WAIT transaction will be put on hold until the conflict is resolved.

If a LOCK TIMEOUT is specified for the WAIT transaction, waiting will continue only for the number of seconds specified in this clause.If the lock is unresolved at the end of the specified interval, the error message “Lock time-out on wait transaction” is returned to the client.

Lock resolution behaviour can vary a little, depending on the transaction isolation level.

NO WAIT Mode

In the NO WAIT mode, a transaction will immediately throw a database exception if a conflict occurs.

Note

LOCK TIMEOUT is a separate transaction option, but can only be used for WAIT transactions.Specifying LOCK TIMEOUT with a NO WAIT transaction will raise an error “invalid parameter in transaction parameter block -Option isc_tpb_lock_timeout is not valid if isc_tpb_nowait was used previously in TPB”