Filter
Top Products
Product Environment 9-23
Two-Phase Commit and Automatic Recovery
Two-Phase Commit and Automatic Recovery
The two-phase commit protocol includes automatic recovery in the event of
an uncontrolled shutdown (such as an operating-system failure) experienced
by either the coordinator or a participant OnLine database server. Two types
of recovery mechanics are included in the two-phase commit protocol:
If your OnLine database server is configured for IBM Informix STAR and you
experience a failure, you must restart the sqlexecd daemon when you reini-
tialize. To do this, log in as root and enter the following commands at the
system prompt when you are ready to reinitialize OnLine:
tbmode -ky ## Ensure all processes are terminated
## and shared memory has been detached.
tbinit ## Reinitialize shared memory and start
## OnLine in online mode. Use tbinit -s
## to start OnLine in quiescent mode.
sqlexecd ## Restart the INFORMIX-STAR daemon.
The sqlexecd command can take a servicename argument, although a default
is assumed. For more information about the servicename value for your
OnLine database server, refer to theIBM Informix NET and IBM Informix STAR
I
nstallation and Configuration Guide. (The servicename value is stored in the
$INFORMIXDIR/etc/sqlhosts file.)
Coordinator Recovery
Coordinator recovery occurs automatically whenever a database server
process acting as coordinator completes the precommit phase and decides to
commit the transaction, but is terminated before the two-phase commit
protocol can be completed. During coordinator recovery, a new coordinator
database server process is spawned to complete the two-phase commit
protocol and ensure that the transaction is completed by every participating
OnLine database server. Figure 9-6 on page 9-25 illustrates coordinator
recovery.
Coordinator
recovery
The coordinating database server process is terminated
prematurely.
Participant
recovery
The database server process at a participating OnLine
database server is terminated prematurely.