Number of cleaners to allocate

You must configure one cleaner for each disk that your applications update frequently. However, you must also consider the length of your LRU queues and frequency of checkpoints.

Another factor that influences whether page cleaners keep up with the number of pages that require cleaning is whether you have enough page-cleaner threads allocated. The percent of dirty pages might exceed the BUFFERPOOL value specified for lru_max_dirty in some queues because no page cleaners are available to clean the queues. After a while, the page cleaners might be too far behind to catch up, and the buffer pool becomes dirtier than the percent that you specified in lru_max_dirty.

For example, suppose that the CLEANERS parameter is set to 8, and you increase the number of LRU queues from 8 to 12. You can expect little in the way of a performance gain because the 8 cleaners must now share the work of cleaning an additional 4 queues. If you increase the number of CLEANERS to 12, each of the now-shortened queues can be more efficiently cleaned by a single cleaner.

Setting CLEANERS too low can cause performance to suffer whenever a checkpoint occurs because page cleaners must flush all modified pages to disk during checkpoints. If you do not configure a sufficient number of page cleaners, checkpoints take longer, causing overall performance to suffer.

For more information, see Flush buffer-pool buffers.


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