Asynchronous prefetch activity report

This section reports asynchronous prefetch activity for all caches.

For information on asynchronous prefetch for each database device, see “Disk I/O management”.

“Total APFs Requested” reports the total number of pages eligible to be pre fetched, that is, the sum of the look-ahead set sizes of all queries issued during the sample interval. Other rows in “Asynchronous Prefetch Activity” provide detail in the three following categories:

APFs issued

“APFs Issued” reports the number of asynchronous prefetch requests issued by the system during the sample interval.

APFs denied due to

This section reports the reasons that APFs were not issued:

APF buffers found in cache

This section reports how many buffers from APF look-ahead sets were found in the data cache during the sample interval. Asynchronous prefetch tries to find a page it needs to read in the data cache using a quick scan without holding the cache spinlock. If that does not succeed, it then performs a thorough scan holding the spinlock.