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1-38 IBM Informix OnLine Database Server Administrator’s Guide
Shared-Memory Parameter Guidelines
DB-Monitor does not prompt for this value during initialization. You can tune
this parameter to affect performance. Refer to page 5-19.
LTXHWM
LTXHWM specifies the “long transaction high-water mark.” In the logical log,
LTXHWM is the percentage of available logical log space that, when filled,
triggers the tbinit daemon to check for long transactions. If a long transaction
is found, the transaction is aborted and the executing OnLine database server
process rolls back all modifications associated with this transaction.
The default value for
LTXHWM is 50 percent. This means that up to 50 percent
of the available log space can be spanned by one user's transaction. When this
level is exceeded, the OnLine database server process is signalled to immedi-
ately roll back that transaction. The rollback procedure continues to generate
logical log records, however, so the logical log continues to fill. This is the
reason for the LTXEHWM parameter.
DB-Monitor does not prompt for this value during initialization. Refer to
page 2-159 for more information about LTXHWM.
LTXEHWM
LTXEHWM specifies the “long transaction, exclusive access, high-water
mark.” The LTXEHWM must be a higher percentage than the LTXHWM
percentage. If the logical logs fill to LTXEHWM, the long transaction currently
being rolled back (refer to LTXHWM) is given “exclusive” access to the logical
log. The term “exclusive” is not entirely accurate. Most OnLine activity is
suspended until the transaction has completed its rollback, but transactions
that are in the process of rolling back or committing retain access to the
logical log.
The default value for LTXEHWM is 60 percent.
DB-Monitor does not prompt for this value during initialization. Refer to
page 2-159 for more information about LTXEHWM.