BufferPool Performance Analysis Beyond the Basic Hit Ratio.....

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7285+QW0198FC DS C

7287+QW0198GP EQU C'G'

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7289+QW0198RP EQU C'R'

7291+QW0198PS DS C

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7307+QW0198DR EQU C'D'

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DATABASE ID PAGESET OBID BUFFERPOOL ID FUNCTION CODE GET PAGE REQUEST SET WRITE INTENT REQUEST RELEASE PAGE REQUEST PAGE STATUS IN BUFFER POOL APPLICABLE ONLY WHEN QW0198FC = 'G'. QW0198PS=X'00' WHEN QW0198FC='S' OR 'R' PAGE HIT IN BUFFERPOOL PAGE MISSED IN BUFFERPOOL NOREAD REQUEST ACCESS TYPE - QW1098AT IS NOT APPLICABLE WHEN QW0198FC = 'S' QW0198AT = X'00' WHEN QW0198FC = 'S' CONSTANTS...............................** SEQUENTIAL ACCESS (GET PAGE) RANDOM ACCESS (GET PAGE) RIDLIST ACCESS (GET PAGE) STANDARD REQUEST (RELEASE PAGE) DESTRUCTIVE REQUEST (RELEASE PAGE) MRU SCHEME APPLIED (RELEASE PAGE) PAGE NUMBER ACE ADDRESS

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Notes:

The 198 record provides most of the access information we need, with the exception of Dynamic Prefetch activity. It doesn’t tell us about read activity, or how many pages were actually brought in by a prefetch read.

It is quite important to understand that the first Getpage (GP) for a prefetched block could be ‘miss’, but the next 31 will absolutely be hits. This creates, at worst, an application hit ratio of 97%. It also doesn't tell us how long the application might have waited for the prefetch to complete. For our purposes in this presentation we are not concerned with I/O wait or elapsed times, although can easily be calculated from the 6 & 7 records.

Note the DBID and OBID in this record and the next two records. This must be translated to a NAME for it to make sense. Therefore, we also need a ‘105’ trace record, or must query the catalog to match the trace records to a useful object name.