Marko Mäkelä d2c593c2a6 MDEV-22877 Avoid unnecessary buf_pool.page_hash S-latch acquisition ... MDEV-15053 did not remove all unnecessary buf_pool.page_hash S-latch acquisition. There are code paths where we are holding buf_pool.mutex (which will sufficiently protect buf_pool.page_hash against changes) and unnecessarily acquire the latch. Many invocations of buf_page_hash_get_locked() can be replaced with the much simpler buf_pool.page_hash_get_low(). In the worst case the thread that is holding buf_pool.mutex will become a victim of MDEV-22871, suffering from a spurious reader-reader conflict with another thread that genuinely needs to acquire a buf_pool.page_hash S-latch. In many places, we were also evaluating page_id_t::fold() while holding buf_pool.mutex. Low-level functions such as buf_pool.page_hash_get_low() must get the page_id_t::fold() as a parameter. buf_buddy_relocate(): Defer the hash_lock acquisition to the critical section that starts by calling buf_page_t::can_relocate().		2020-06-12 16:22:03 +03:00
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ibuf0ibuf.cc	MDEV-22877 Avoid unnecessary buf_pool.page_hash S-latch acquisition	2020-06-12 16:22:03 +03:00