PM70270: A LOWER BUFFER HIT RATIO OR MORE SYNCHRONOUS I/O IF VPSEQT IS SET TO A SMALL VALUE
- If customers have a large virtual buffer pool (VPSIZE) setting and at the same time a very low sequential page threshold setting, an impact is likely.
- When a random Getpage buffer miss resulted in DB2 stealing a buffer from the sequential LRU chain, DB2 did not remove the buffer from the sequential LRU chain when it should - reclasification. This meant that random pages were more likely constricted by VPSEQT. Therefore in some cases, recently used buffers were stolen more quickly than less recently used buffers, resulting in a a lower buffer hit ratio or more synchronous I/O. The impact of this problem is relatively small if the default VPSEQT value of 80% is used, but the impact is likely to be large if VPSEQT is set low.
- This APAR can deliver a significant performance improvement in terms of
reducting scheduled synchronous I/O's triggered by hitting the VPSEQT
and re- enabling the page reclassification when buffers are