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Product Environment 9-41
Heuristic End-Transaction
As a consequence, the transaction remains open. The open transaction
prevents you from backing up logical log files and freeing space in the logical
log. As the logical log continues to fill, it might reach the point specified by
the exclusive-access, long-transaction high-water mark, LTXEHWM. If this
occurs, normal processing is suspended. At some point after the LTXEHWM
high-water mark is reached, you must decide if the open transaction is
endangering your logical log. The danger is that if the logical log fills
completely, OnLine shuts down and you must perform a data restore.
You must decide if it is right for you to kill the transaction and protect your
system against the possibility of filling the logical log, despite all the
problems associated with executing tbmode -Z, or if it is right for you to wait
and see if communication with the coordinator can be reestablished in time
to end the transaction before the logical log fills.
The tbmode -Z address command is intended for use only if communication
between the coordinator and the participant is broken. To ensure that this is
the case, the tbmode -Z command does not execute unless the database
server process that was executing the piece of work has been dead for the
amount of time specified by TXTIMEOUT. (Refer to page 9-57 for a definition
of the TXTIMEOUT configuration parameter.)
The address parameter is obtained from tbstat -u output. Refer to page 9-58.
Refer to page 7-69 for additional tbmode -Z syntax information.
When you execute tbmode -Z, you direct the tbmode process to remove the
transaction entry that is located at the specified address from the transaction
table. Two records are written in the logical log to document the action. The
records are type ROLLBACK and ENDTRANS, or if the transaction was already
heuristically rolled back, ENDTRANS only. The following message is written
to the participant OnLine message log: (refer to page 8-29 for a complete
description of the message)
(time) Transaction Completed Abnormally (endtx): tx=address
flags:0xnn user username tty ttyid
Your action to remove all transaction information from either the coordinator
or the participant OnLine shared memory breaks the two-phase commit
protocol.