How are the following alarms calculated and what are they used for?
These alarms will be fired when the corresponding cache hit ratio of the database's or member's I/O activity falls below a predefined threshold.
This is overall hit ratio of logical reads to physical reads, namely: the percentage of database page I/O requests that were satisfied from the buffer cache and therefore did not have to perform disk reads. This ratio measures how efficiently DB2 is using the memory allocated to its buffer cache.
(1 - physical_reads/(logical_reads + 1))*100
The Database Overall Cache Hit Ratio value can be reflected in the Databases Overview screen under Memory | Buffer Pool
If this alarm fires, consider investigating the related pool activity and increasing the bufferpool size in the DB2 instance.
When either the "DB2 - Member Index Cache Hit Ratio" or "DB2 - Database Index Cache Hit Ratio" alarms fire, the index related pool activity should be investigated to identify the root cause of the low index hit ratio.
The index cache hit ratio can be calculated using the following formula:
(1 - POOL_INDEX_P_READS/(POOL_INDEX_L_READS + 1))*100
One consideration in resolving this issue is to enlarge the bufferpool size.
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