Performance Tuning for Content Manager

248 Performance Tuning for Content Manager

You can save disk storage for databases that are not accessed frequently by

setting the parameter to 2. For databases enabled for roll-forward recovery, set

the parameter larger to avoid the overhead of allocating new logs almost

immediately.

Use the database system monitor to help size the primary log files. Observing

the following monitor values over a period of time will aid in better tuning

decisions, because average values might be more representative of your

ongoing requirements:

 sec_log_used_top (maximum secondary log space used)

 tot_log_used_top (maximum total log space used)

 sec_logs_allocated (secondary logs allocated currently)

8.6.37 Number of secondary log files (LOGSECOND)

Impact

DB - Medium

Description

This parameter specifies the number of secondary log files that are created and

used for recovery log files (only as needed). When the primary log files become

full, the secondary log files (of size LOGFILSIZ) are allocated one at a time as

needed, up to a maximum number as controlled by this parameter. An error code

will be returned to the application, and the database will be shut down, if more

secondary log files are required than are allowed by this parameter.

If you set LOGSECOND to -1, the database is configured with infinite active log

space. There is no limit on the size or the number of in-flight transactions running

on the database. You still use the LOGPRIMARY and LOGFILSIZ configuration

parameters to specify how many log files DB2 should keep in the active log path.

If DB2 needs to read log data from a log file, but the file is not in the active log

path, DB2 will invoke the user exit program to retrieve the log file from the archive

to the active log path. (DB2 retrieves the files to the overflow log path, if you have

configured one.)

When the log file is retrieved, DB2 caches this file in the active log path so that

other reads of log data from the same file will be fast. DB2 manages the retrieval,

caching, and removal of these log files as required.

If your log path is a raw device, you must configure the OVERFLOWLOGPATH

configuration parameter and set the userexit configuration parameter to Yes in

order to set LOGSECOND to -1.