Performance Tuning for Content Manager

Chapter 8. Tuning DB2 for Content Manager 223

Tuning this parameter is particularly important when several sections are used

initially, and then only a few are run repeatedly. If the cache is too large, memory

is wasted holding copies of the initial sections.

The limit specified by the PCKCACHESZ parameter is a soft limit. This limit may

be exceeded, if required and if memory is still available in the database shared

set. You can use the PKG_CACHE_SIZE_TOP monitor element to determine the

largest that the package cache has grown.

8.6.18 Log buffer size (LOGBUFSZ)

Impact

DB - High

Description

This parameter enables you to specify the amount of the database heap (defined

by the DBHEAP parameter) to use as a buffer for log records before writing these

records to disk.

The log records are written to disk when one of the following actions occurs:

 A transaction commits or a group of transactions commit, as defined by the

MINCOMMIT configuration parameter.

 The log buffer is full.

 As a result of some other internal database manager event.

This parameter must be less than or equal to the DBHEAP parameter. Buffering

the log records will result in more efficient logging file I/O because the log records

will be written to disk less frequently, and more log records will be written at each

time.

Default values (range)

8 (4 - 4,096) 4-KB pages for 32-bit platforms

8 (4 - 65,535) 4-KB pages for 64-bit platforms

Note: The package cache is a working cache, so you cannot set this

parameter to zero. There must be sufficient memory allocated in this cache to

hold all sections of the SQL statements that are currently being run. If there is

more space allocated than currently needed, then sections are cached. These

sections can simply be run the next time they are needed without having to

load or compile them.