Identifier:db2.tbsp_pool_hit_ratio
Database Object Monitored:Table Space
Category:Buffer Pool and I/O
Description:Overall buffer pool hit ratio, includes index plus data activity (percent effective)
Equation:100 * (1 - (DELTA(tablespace.pool_data_p_reads + tablespace.pool_index_p_reads) / DELTA(tablespace.pool_data_l_reads + tablespace.pool_index_l_reads)))
Usage Notes:This value is a measure of the effectiveness of the buffer pool. The more data found in the buffer pool, the better it is for performance since it avoids unneccessary input and output.
The configuration of the buffer pool is the single most important tuning area, since most data manipulation for connected applications, excluding large objects and long field data, takes place here.
If the Buffer Pool Hit Ratio is low (less than 90% for decision support, less than 50% for query-only and online transaction procession), increase the size of the buffer pool by increasing buffpage.
As a rule, the buffer pool should be as large as possible. Increase buffpage until you see an increase in swapping (indicated by an operating system monitor).
Note that the buffer pool is allocated from the same shared memory segment as the lock list, database heap, and utility heap (determined by configuration parameters locklist, dbheap, and util_heap_sz respectively).
Also consider the impact of prefetch on the buffer pool. Refer to db2.tbsp_avg_sync_read_time and db2.db_avg_sync_read_time.
| Note: | For multiple buffer pools, the data is combined and only the aggregate number is returned. |