USELASTCOMMITTED configuration parameter

Use the USELASTCOMMITTED configuration parameter to specify the isolation level for which the LAST COMMITTED feature of the COMMITTED READ isolation level is implicitly in effect.

onconfig.std value: USELASTCOMMITTED "NONE"
default value: "NONE"
values: "NONE" = No isolation level identified. If your session encounters an exclusive lock when attempting to read a row in the Committed Read, Dirty Read, Read Committed, or Read Uncommitted isolation level, your transaction cannot read that row until the concurrent transaction that holds the exclusive lock is committed or rolled back.; "COMMITTED READ" = All transactions from a Committed Read isolation level are treated as last committed transactions. The database server reads the most recently committed version of the data when it encounters an exclusive lock while attempting to read a row in the Committed Read or Read Committed isolation level.; "DIRTY READ" = All transactions from a Dirty Read isolation level are treated as last committed transactions. The database server reads the most recently committed version of the data if it encounters an exclusive lock while attempting to read a row in the Dirty Read or Read Uncommitted isolation level.; "ALL" = All transactions from both Committed Read and Dirty Read isolation levels are treated as last committed transactions. database server reads the most recently committed version of the data if it encounters an exclusive lock while attempting to read a row in the Committed Read, Dirty Read, Read Committed, or Read Uncommitted isolation level.
takes effect: After you edit your onconfig file and restart the database server.; When you reset the value dynamically in your onconfig file by running the onmode -wf command.; When you reset the value in memory by running the onmode -wm command.

Usage

The LAST COMMITTED feature can reduce the risk of locking conflicts between concurrent transactions on tables that have exclusive row locks. The USELASTCOMMITTED configuration parameter can also enable LAST COMMITTED semantics for READ COMMITTED and READ UNCOMMITTED isolation levels of the SET TRANSACTION statement.

The USELASTCOMMITTED configuration parameter only works with tables that have been created or altered to have ROW as their locking granularity. Tables created without any explicit lock mode setting will use the default setting in DEF_TABLE_LOCKMODE. If DEF_TABLE_LOCKMODE is set to PAGE, the USELASTCOMMITTED configuration parameter cannot enable access to the most recently committed data in tables on which uncommitted transactions hold exclusive locks, unless the tables were explicitly altered to have ROW level of locking granularity.

Use with Shared Disk secondary database servers

The USELASTCOMMITTED configuration parameter is also valid on Shared Disk (SD) secondary database servers. The following table shows valid values for the USELASTCOMMITTED configuration parameter on SD secondary servers and their descriptions.

Table 1. Valid secondary server USELASTCOMMITTED values
USELASTCOMMITTED value	Description
NONE	COMMITTED READ LAST COMMITTED is not the default isolation level for sessions
COMMITTED READ	COMMITTED READ LAST COMMITTED is the default isolation level for all sessions with Committed Read isolation
DIRTY READ	COMMITTED READ LAST COMMITTED is the default isolation level for all sessions with Dirty Read isolation
ALL	COMMITTED READ LAST COMMITTED is the default isolation level for all sessions with Committed Read or Dirty Read isolation