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MDEV-22871: Reduce InnoDB buf_pool.page_hash contention

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The rw_lock_s_lock() calls for the buf_pool.page_hash became a
clear bottleneck after MDEV-15053 reduced the contention on
buf_pool.mutex. We will replace that use of rw_lock_t with a
special implementation that is optimized for memory bus traffic.

The hash_table_locks instrumentation will be removed.

buf_pool_t::page_hash: Use a special implementation whose API is
compatible with hash_table_t, and store the custom rw-locks
directly in buf_pool.page_hash.array, intentionally sharing
cache lines with the hash table pointers.

rw_lock: A low-level rw-lock implementation based on std::atomic<uint32_t>
where read_trylock() becomes a simple fetch_add(1).

buf_pool_t::page_hash_latch: The special of rw_lock for the page_hash.

buf_pool_t::page_hash_latch::read_lock(): Assert that buf_pool.mutex
is not being held by the caller.

buf_pool_t::page_hash_latch::write_lock() may be called while not holding
buf_pool.mutex. buf_pool_t::watch_set() is such a caller.

buf_pool_t::page_hash_latch::read_lock_wait(),
page_hash_latch::write_lock_wait(): The spin loops.
These will obey the global parameters innodb_sync_spin_loops and
innodb_sync_spin_wait_delay.

buf_pool_t::freed_page_hash: A singly linked list of copies of
buf_pool.page_hash that ever existed. The fact that we never
free any buf_pool.page_hash.array guarantees that all
page_hash_latch that ever existed will remain valid until shutdown.

buf_pool_t::resize_hash(): Replaces buf_pool_resize_hash().
Prepend a shallow copy of the old page_hash to freed_page_hash.

buf_pool_t::page_hash_table::n_cells: Declare as Atomic_relaxed.

buf_pool_t::page_hash_table::lock(): Explain what prevents a
race condition with buf_pool_t::resize_hash().
This commit is contained in:
Marko Mäkelä
2020-06-18 13:38:30 +03:00
parent cfd3d70ccb
commit 5155a300fa
23 changed files with 478 additions and 327 deletions
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mysql-test/suite/perfschema/r/sxlock_func.result
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@@ -17,7 +17,6 @@ wait/synch/sxlock/innodb/dict_table_stats
wait/synch/sxlock/innodb/fil_space_latch
wait/synch/sxlock/innodb/fts_cache_init_rw_lock
wait/synch/sxlock/innodb/fts_cache_rw_lock
wait/synch/sxlock/innodb/hash_table_locks
wait/synch/sxlock/innodb/index_online_log
wait/synch/sxlock/innodb/index_tree_rw_lock
wait/synch/sxlock/innodb/trx_i_s_cache_lock