PS-11120 [9.7]: Reduce contention on BUF_BLOCK_MUTEX by reading ahead the access_time#6031
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PS-11120 [9.7]: Reduce contention on BUF_BLOCK_MUTEX by reading ahead the access_time#6031polchawa-percona wants to merge 1 commit into
polchawa-percona wants to merge 1 commit into
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…ccess_time This patch reduces contention inside buf_page_optimistic_get. We acquire there the BUF_BLOCK_MUTEX twice. But the second time we acquire only to update the access time. Given that we would update the access time only if it was zero, we could avoid acquiring the mutex when we knew that the access time was already non-zero. This we could learn the first time we acquired the mutex by reading the access time field of the page. Note: the second time we acquired the mutex, we re-check if it still was zero anyway, so the patch is safe and allows to save significant number of times we needed to acquire the mutex. This is a contribution from: Anna Glasgall (with a minor fix).
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https://perconadev.atlassian.net/browse/PS-11120
This patch reduces contention inside buf_page_optimistic_get. We acquire the BUF_BLOCK_MUTEX twice there. But the second time we acquire it only to update the access time. Given that we would update the access time only if it was zero, we could avoid acquiring the mutex when we knew that the access time was already non-zero. This we could learn the first time we acquired the mutex by reading the access time field of the page.
Note:
the second time we acquired the mutex, we would check again if it still was zero anyway
we never reset the access time to zero (unless we reinitialize new page)
the page would not be reinitialized meanwhile, because the first time we accessed it, we "fix it" (call buf_block_buf_fix_inc), which is to keep the page alive (purpose of fixing) until it is "unfixed" (much later)
The patch is safe and allows us to save a significant number of times we needed to acquire the mutex.
This is a contribution from: Anna Glasgall aglasgal@akamai.com / Akamai, with a minor fix added.