DB2 Version 9.7 for Linux, UNIX, and Windows

pool_drty_pg_steal_clns - Buffer pool victim page cleaners triggered monitor element

The number of times a page cleaner was invoked because a synchronous write was needed during the victim buffer replacement for the database.

Table 1. Table Function Monitoring Information
Table Function	Monitor Element Collection Command and Level
MON_GET_BUFFERPOOL table function - Get buffer pool metrics	DATA OBJECT METRICS BASE

Table 2. Snapshot Monitoring Information
Snapshot Level	Logical Data Grouping	Monitor Switch
Database	dbase	Buffer Pool

For snapshot monitoring, this counter can be reset.

Table 3. Event Monitoring Information
Event Type	Logical Data Grouping	Monitor Switch
Database	event_db	-

Usage

Using the following formula, you may calculate what percentage of all cleaner invocations are represented by this element:

        pool_drty_pg_steal_clns
     / (pool_drty_pg_steal_clns
      + pool_drty_pg_thrsh_clns
      + pool_lsn_gap_clns)

If this ratio is low, it may indicate that you have defined too many page cleaners. If your chngpgs_thresh configuration parameter is set too low, you may be writing out pages that you will dirty later. Aggressive cleaning defeats one purpose of the buffer pool, that is to defer writing to the last possible moment.

If this ratio is high, it may indicate that you have not defined enough page cleaners. Not having enough page cleaners increases recovery time after failures.

When the DB2_USE_ALTERNATE_PAGE_CLEANING registry variable is OFF:

The pool_drty_pg_steal_clns monitor element is inserted into the monitor stream.
The pool_drty_pg_steal_clns monitor element counts the number of times a page cleaner was invoked because a synchronous write was needed during the victim buffer replacement for the database.

When the DB2_USE_ALTERNATE_PAGE_CLEANING registry variable is ON:

The pool_drty_pg_steal_clns monitor element inserts 0 into the monitor stream.
There is no explicit triggering of the page cleaners when a synchronous write is needed during victim buffer replacement. To determine whether or not the right number of page cleaners is configured for the database or for specific buffer pools, please refer to the pool_no_victim_buffer monitor element.

Note: Although dirty pages are written out to disk, the pages are not removed from the buffer pool right away, unless the space is needed to read in new pages.