3-40 IBM Informix OnLine Database Server Administrator’s Guide
Free a Logical Log File
Referto page 3-15for a discussion about the importance of freeing the logical
log files in a timely manner. Refer topage 3-26 for information about the
logical log file status flags. Refer to page3-27 for more information about
how the logical log files rotate through ID numbers.
OnLine user processes attempt to free logical log files under the following
conditions:
■The first OnLine user process that writes to a new logical log file
attempts to free the previous log.
■Eachtime tbtape completes its backup of a logical log file, it attempts
to free the log file.
■Each time an OnLine database server process commits or rolls back
atransaction, it attempts to free the logical log file in which the trans-
action began.
■Eachtime an OnLine user process attempts to use the next logical log
file, it attempts to free the log file, if it is not already free.
Long Transactions
Alongtransaction is an open transaction that starts in the first logical log file
(theone with the lowest ID number at any time). Since a logical log file cannot
be freed until all records within the file are associated with closed transac-
tions, the long transaction prevents the first logical log file from becoming
free and available for reuse. The logged data must be kept intact (not
overwritten) in case the open transaction must be rolled back.
Ifa long transaction were permitted to continue, it could pose a threat to your
OnLine processing. If OnLine attempted to fill the next logical log file in
sequence but found that it was unreleased (statusU) and not freed, OnLine
processing would be suspended to protect the data in the logical log file.
Long transactions are handled automatically by OnLine. For further infor-
mation about how OnLine handles long transactions internally, refer to the
discussion of the LTXHWM and LTXEHWM configuration file parameters on
page 2-159.