Product Environment 9-41
Heuristic End-Transaction
As a consequence, the transaction remains open. The open transaction
preventsyou 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 theLTXEHWM
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
problemsassociated 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 -Zaddress command is intended for use only if communication
betweenthe coordinator and the participant is broken. To ensure that this is
the case, thetbmode -Z command does not execute unless the database
server process that was executing the piece of work has been dead for the
amountof 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 topage 9-58.
Refer topage 7-69 for additionaltbmode -Z syntax information.
Whenyou execute tbmode -Z, you direct the tbmode process to remove the
transactionentry that is located at the specified address from the transaction
table. Two records are written in the logical log to document the action. The
recordsare type ROLLBACK and ENDTRANS,or if the transaction was already
heuristicallyrolled back, ENDTRANS only. The following message is written
to the participant OnLine message log: (refer topage 8-29 for a complete
description of the message)
(time) Transaction Completed Abnormally (endtx): tx=address
flags:0xnn user username tty ttyid
Youraction to remove all transaction information from either the coordinator
or the participant OnLine shared memory breaks the two-phase commit
protocol.