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_data_writes counter |
Description: Indicates the number of times a buffer pool data page was physically written to disk.
Usage: If a buffer pool data page is written to disk for a high percentage of the "Buffer Pool Data Physical Reads", you may be able to improve performance by increasing the number of buffer pool pages available for the database.
A buffer pool data 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 data page can be written by an asynchronous page-cleaner agent before the buffer pool space is required. These asynchronous page writes are included in the value of this element in addition to synchronous page writes (see "Buffer Pool Asynchronous Data Writes").
When calculating this percentage, disregard the number of physical reads required to initially fill the buffer pool. To determine the number of pages written:
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 buffer pool pages contain updated data, which must be written to disk. However, if the updated pages can be used by other units of work before being written out, the buffer pool can save a write and a read, which will improve your performance.
See the Administration Guide for more information about buffer pool size.