DB2 Version 9.7 for Linux, UNIX, and Windows

pool_async_data_read_reqs - Buffer pool asynchronous read requests monitor element

The number of asynchronous read requests by the prefetcher to the operating system. These requests are typically large block I/Os of multiple pages.

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
MON_GET_TABLESPACE table function - Get table space metrics	DATA OBJECT METRICS BASE

Table 2. Snapshot Monitoring Information
Snapshot Level	Logical Data Grouping	Monitor Switch
Database	dbase	Buffer Pool
Table Space	tablespace	Buffer Pool
Buffer Pool	bufferpool	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	-
Tablespaces	event_tablespace	-

Usage

To calculate the average number of data pages in each read request, use the following formula:

 pool_async_data_reads / pool_async_data_read_reqs

This average can help you determine the average read I/O size used by the prefetcher. This data can also be helpful in understanding the large block I/O requirements of the measured workload.

The maximum size of a prefetcher read I/O is the value specified on the EXTENTSIZE option of the CREATE TABLESPACE statement for the table space involved, but it can be smaller under some circumstances:

when some pages of the extent are already in the buffer pool
when exceeding operating system capabilities
when the EXTENTSIZE option value is very large, such that doing a large I/O would be detrimental to overall performance