9-44 IBM Informix OnLine Database Server Administrator’s Guide
Two-Phase Commit and Logical Log Records
Two-Phase Commit and Logical Log RecordsSupport of two-phase commit requires five additional logical log records.
These records can be used to detect heuristic decisions and, if required, to
helpyou perform a manual recovery in the event of an inconsistent database
system.The five records and their contents are described in this 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
TheBEGPREP logical log record is only written by the coordinator OnLine
database server to record the start of a global transaction.
Theoutput from tblog contains three fields: type, flags, and number of partic-
ipants. The value of the flags is always zero in theIBM Informix STAR
environment. The number of participants is expressed as an integer. The
output appears as follows:
BEGPREP 0 number_of_participants
PREPARE
ThePREPARE 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.
Theoutput from tblog contains two fields: type and coordinator server name,
specified as the DBSERVERNAME. The output appears as follows:
PREPARE coordinator_DBSERVERNAME
Figure9-10 on page 9-46 showsthe logical log records that are written when
a transaction is committed.
Figure9-11 on page 9-49 showsthe logical log records that are written when
a piece of work is heuristically rolled back.
Figure9-12 on page 9-50 showsthe logical log records that are written when
a piece of work is heuristically ended.