IBM 000-8697 Manual Do Utilizador

9-50

IBM Informix OnLine Database Server Administrator’s Guide

Two-Phase Commit and Logical Log Records

Heuristic End-Transaction Records

illustrates the writing sequence of the logical log records during

a heuristic end-transaction. The event is always the result of an administrator
executing tbmode -Z at a participant OnLine database server after the partic-
ipant has sent a message: “can commit.” (Refer to

page 9-40

for a description

of a heuristic end-transaction.) In

Figure 9-12

, the heuristic end-transaction is

assumed to have occurred at the P1 participant.

Important: The transaction is inconsistently implemented.

Figure 9-12

Writes of

logical log records

during a heuristic

end-

transaction

All Participants:
Writes log record: TABLOCKS.
Writes and flushes log record: PREPARE.
Sends message: “commit ok.”

Coordinator:
Writes log record: BEGPREP.
Sends message: “precommit.”

P1 Participant:
Sends message: “Transaction status unknown.”

Coordinator:
Writes and flushes log record: COMMIT.
Sends message: “commit.”

Within P1 Participant’s Environment:
tbmode -Z is executed.
Writes log record: ROLLBACK.
Writes log record: ENDTRANS.
Message is written in OnLine message log.

Start Protocol

Transaction is

inconsistently implemented

Coordinator:
Assumes “unknown” status means “committed.”
Writes log record: ENDTRANS.

P2 and P3 Participants:
Send message: “committed.”