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Jon Olav Hauglid authored
This was a deadlock between CREATE/ALTER/DROP EVENT and a query accessing both the mysql.event table and I_S.GLOBAL_VARIABLES. The root of the problem was that the LOCK_event_metadata mutex was used to both protect the "event_scheduler" global system variable and the internal event data structures used by CREATE/ALTER/DROP EVENT. The deadlock would occur if CREATE/ALTER/DROP EVENT held LOCK_event_metadata while trying to open the mysql.event table, at the same time as the query had mysql.event open, trying to lock LOCK_event_metadata to access "event_scheduler". This bug was fixed in the scope of Bug#51160 by using only LOCK_global_system_variables to protect "event_scheduler". This makes it so that the query above won't lock LOCK_event_metadata, thereby preventing this deadlock from occuring. This patch contains no code changes. Test case added to lock_sync.test.
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