Details
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Bug
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Status: Closed (View Workflow)
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Blocker
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Resolution: Fixed
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10.6, 10.10(EOL), 10.11, 11.0(EOL), 11.1(EOL), 11.2(EOL)
Description
While running performance tests with a small buffer pool, I encountered an anomaly where InnoDB would hang because of running out of buffer pool. There would be some actually clean blocks at buf_pool.flush_list.start, but these would be skipped by buf_flush_LRU_list_batch(). The buf_pool.flush_list.end is being trimmed by periodic calls to buf_pool.get_oldest_modification(). I suspect that the entire buf_pool.LRU would be skipped because of being buffer-fixed, latched, or registered in buf_pool.flush_list due to the MDEV-26010 optimization.
This seems to be a 10.6 regression due to MDEV-26827.
MDEV-32050 would make this problem worse by allowing the purge_coordinator_task to buffer-fix a large number of pages.
Attachments
Issue Links
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Activity
In my tests on a non-debug build, the race condition that is fixed by the second hunk of the patch caused a shutdown hang as well as a
InnoDB: Failing assertion: list.count > 0
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in buf_pool_t::insert_into_flush_list() during a mtr_t::commit().
I think that the following patch fixes this.
diff a/storage/innobase/buf/buf0flu.cc b/storage/innobase/buf/buf0flu.cc--- a/storage/innobase/buf/buf0flu.cc+++ b/storage/innobase/buf/buf0flu.cc@@ -1246,16 +1246,14 @@ static void buf_flush_LRU_list_batch(ulint max, bool evict,ut_ad(state >= buf_page_t::FREED);ut_ad(bpage->in_LRU_list);- switch (bpage->oldest_modification()) {- case 0:+ if (!bpage->oldest_modification())+ {evict:if (state != buf_page_t::FREED &&(state >= buf_page_t::READ_FIX || (~buf_page_t::LRU_MASK & state)))continue;buf_LRU_free_page(bpage, true);++n->evicted;- /* fall through */- case 1:if (UNIV_LIKELY(scanned & 31))continue;mysql_mutex_unlock(&buf_pool.mutex);@@ -1271,7 +1269,11 @@ static void buf_flush_LRU_list_batch(ulint max, bool evict,switch (bpage->oldest_modification()) {case 1:mysql_mutex_lock(&buf_pool.flush_list_mutex);- buf_pool.delete_from_flush_list(bpage);+ if (ut_d(lsn_t lsn=) bpage->oldest_modification())+ {+ ut_ad(lsn == 1); /* It must be clean while we hold bpage->lock */+ buf_pool.delete_from_flush_list(bpage);+ }mysql_mutex_unlock(&buf_pool.flush_list_mutex);/* fall through */Before
MDEV-26827, we were acting upon oldest_modification==1 while already holding buf_pool.flush_list_mutex. Both regressions were introduced by me inMDEV-26827.