BufferPool is very important component in db2 architecture. It is the place where the data is cached for optimal performance. BufferPool hit ratio is used to measure the performance. If a data page or index page is found in the BufferPool it is called as logical read and if it is not found there then retrieval from the disk is performed. Disk reads are generally very costly and should be reduced as much as possible. So you need to measure the BufferPool hit ratio at regular intervals and then adjust the size accordingly.

Two important components acting on BufferPool are prefetchers and page cleaners. Prefetchers fetch the data from the disk in advance to the pool in the form of extents. Page cleaners help in flushing the data from BufferPool to disk at regular intervals. Page cleaning depends on the SOFTMAX and log committing settings. Alternate page cleaning can be turned on to improve the page cleaning process and the resources it consumes.

You can assign one BufferPool each for a table space or multiple table spaces can be assigned to a BufferPool. Usually if there is a large table space and highly accessed tables inside the table space it is better to assign a separate BufferPool. Also indexes can be placed in a separate BufferPool if needed. There are hidden BufferPools of 4k,8k,16k,32k page size. Whenever a BufferPool is dropped for some reason, these hidden BufferPools come into picture to accommodate the data assigned to the table space. BufferPools can be monitored using the BufferPool snapshot and also using the DB2pd utility.

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