Tuning database buffer pools

Buffer pools are areas of virtual storage that temporarily store pages of table spaces or indexes.

When an application program accesses a row of a table, Db2 places the page that contains that row in a buffer. Access to data in this temporary storage is faster than accessing data on a disk. If the required data is already in a buffer, the application program does not need to wait for it to be retrieved from disk, so the time and cost of retrieving the page is reduced.

If the row is changed, the data in the buffer must be written back to disk eventually. But that write operation might be delayed until Db2 takes a checkpoint, or until one of the related write thresholds is reached. (In a data sharing environment, however, the writing mechanism is somewhat different. .) The data remains in the buffer until Db2 decides to use the space for another page. Until that time, the data can be read or changed without a disk I/O operation.

Buffer pools reside in the database services address space (ssnmDBM1). The maximum size of a buffer pool is 16 TB.