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9-26 IBM Informix OnLine Database Server Administrator’s Guide

Two-Phase Commit and Automatic Recovery

Participant Recovery

Participant recovery occurs whenever a database server process acting as

participant precommits a piece of work but is terminated before the two-

phase commit protocol canbe completed. Thegoal ofparticipant recovery is

to complete the two-phase commit protocol according to the decision

reached by the coordinating OnLine.

During participant recovery, the piece of work waits for direction that the

work should be committed. If the coordinator is able, it spawns (through

sqlexecd) a new participant database server process to replace the one that

was terminated. The intent is for the coordinator and the new participant

process to complete the two-phase commit protocol.

However, the piece of work only waits a limited amount of time for the

coordinator to reestablish the protocol. This waiting period is speciﬁed as

TXTIMEOUT. (Refer to page 9-57.)

If the waitingperiodelapses beforethecoordinatorhas been ableto spawn a

new participant, the tbinit process at the participant OnLine spawns a new

participant database server process. It is the task of this tbinit-spawned

serverprocesstodeterminethetransactionstatusandcompletetheprotocol.

Figure 9-7 illustrates participant recovery.

Participant failure can occur as a result of either a system failure or the

isolated failure of the participant database server process. If a system failure

occurred, the administrator reinitializes shared memory and restarts the

sqlexecd process. (Refer to page 9-23.) Otherwise, participant recovery

occurs as part of OnLine processing.

As part of normal processing, the tbinit process at the participant OnLine

detects ﬁrst that a two-phase commit protocol was underway, second that a

piece of work had been prepared to commit and third that the participant

database server process that owned the transaction was terminated

prematurely.

Nothing happens yet. The transaction waits to be contacted by the coordi-

nator. If the coordinator’s ﬁnal decision is to commit the piece of work, the

coordinator attempts to contact the participant.

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