Buffer Pool Index Writes



Snapshot Level
Database
Table Space
 
Application
Logical Data Grouping
dbase
tablespace
bp_info
appl
Monitor Switch
Buffer Pool
Buffer Pool
Buffer Pool
Buffer Pool


Resettable
Yes
 


Event Type
Database
Table Space
Connection
Logical Data Grouping
db_event
tablespace_event
conn_event
 


Element Name
Element Type
pool_index_writes
counter

 

Description:  Indicates the number of times a buffer pool index page was physically written to disk.

Usage:  Like a data page, a buffer pool index page is written to disk for the following reasons:

The system does not always write a page to make room for a new one. If the page has not been updated, it can simply be replaced. This replacement is not counted for this element.

The index page can be written by an asynchronous page-cleaner agent before the buffer pool space is required. These asynchronous index page writes are included in the value of this element in addition to synchronous index page writes (see "Buffer Pool Asynchronous Index Writes").

If a buffer pool index page is written to disk for a high percentage of the "Buffer Pool Index Physical Reads", you may be able to improve performance by increasing the number of buffer pool pages available for the database.

When calculating this percentage, disregard the number of physical reads required to initially fill the buffer pool. To determine the number of pages written:

  1. Run your application (to load the buffer)
  2. Note the value of this element
  3. Run your application again
  4. Subtract the value recorded in step 2 from the new value of this element.

In order to prevent the buffer pool from being deallocated between the runnings of your application, you should either:

If all applications are updating the database, increasing the size of the buffer pool may not have much impact on performance, since most of the pages contain updated data which must be written to disk.

See the Administration Guide for more information about buffer pool size.