
9-44 IBM Informix OnLine Database Server Administrator’s Guide
Two-Phase Commit and Logical Log Records
Two-Phase Commit and Logical Log Records
Support of two-phase commit requires five additional logical log records.
These records can be used to detect heuristic decisions and, if required, to
help you performamanual recovery in theeventof an inconsistent database
system. The five recordsand theircontents are described inthis section.(For
more details about how to display and interpret the contents of the logical
log, refer to page 7-55.) The following illustrations of the two-phase commit
protocol are also included in this section:
BEGPREP
The BEGPREP logical log record is only written by the coordinator OnLine
database server to record the start of a global transaction.
Theoutputfromtblogcontainsthreefields:type,flags,and numberofpartic-
ipants. The value of the flags is always zero in the IBM Informix STAR
environment. The number of participants is expressed as an integer. The
output appears as follows:
BEGPREP 0 number_of_participants
PREPARE
The PREPARE logical log record is only written by a participant OnLine
database server to record the ability of the participant to commit the trans-
action, if so instructed.
Theoutputfromtblogcontainstwofields:typeandcoordinatorservername,
specified as the DBSERVERNAME. The output appears as follows:
PREPARE coordinator_DBSERVERNAME
Figure 9-10 on page 9-46 showsthelogicallogrecordsthatarewrittenwhen
a transaction is committed.
Figure 9-11 on page 9-49 showsthelogicallogrecordsthatarewrittenwhen
a piece of work is heuristically rolled back.
Figure 9-12 on page 9-50 showsthelogicallogrecordsthatarewrittenwhen
a piece of work is heuristically ended.
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