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MDEV-25072: Livelock due to innodb_change_buffering_debug

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buf_page_get_low(): Do not try to re-evict the page if it is
multiply buffer-fixed.

In commit 7cffb5f6e8a231a041152447be8980ce35d2c9b8 (MDEV-23399)
a livelock was introduced. If multiple threads are concurrently
requesting the same secondary index leaf page in buf_page_get_low()
and innodb_change_buffering_debug is set, all threads would try
to evict the page in a busy loop, never succeeding because the
block is buffer-fixed by other threads.

Thanks to Roel Van de Paar for reporting the original failure and
Elena Stepanova for producing an "rr replay" trace.
This commit is contained in:
Marko Mäkelä 2021-03-31 14:11:56 +03:00
parent 5eae8c2742
commit 147a317e81
1 changed files with 2 additions and 1 deletions
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3
storage/innobase/buf/buf0buf.cc
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@ -3324,7 +3324,8 @@ re_evict:
buf_flush_lists(ULINT_UNDEFINED, LSN_MAX);
buf_flush_wait_batch_end_acquiring_mutex(false);
if (!fix_block->page.oldest_modification()) {
if (fix_block->page.buf_fix_count() == 1
&& !fix_block->page.oldest_modification()) {
goto re_evict;
}