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MDEV-3917 multiple use locks (GET_LOCK) in one connection.

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The patch contributed by Konstantin Osipov applied.
    Native comments:
      Implement multiple user-level locks per connection.

      GET_LOCK() function in MySQL allows a connection  to hold at most
      one user level lock. Taking a new lock automatically releases the
      old lock, if any.

      The limit of one lock per session existed since  early versions
      of MySQL didn't have a deadlock detector for SQL locks.
      MDL patches in MySQL 5.5 added a deadlock detector,
      so starting from 5.5 it became possible to take multiple locks
      in any order -- a deadlock, should it occur, would be detected
      and an error returned to the client which closed the wait chain.

      This is exactly what is done in this patch: ULLs are moved
      to use MDL subsystem.
This commit is contained in:
Alexey Botchkov
2013-04-12 18:06:51 +05:00
parent ff3407a111
commit 1a600125ff
14 changed files with 869 additions and 353 deletions
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1
sql/sql_reload.cc
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@ -205,6 +205,7 @@ bool reload_acl_and_cache(THD *thd, unsigned long options,
DBUG_ASSERT(!thd || thd->locked_tables_mode ||
!thd->mdl_context.has_locks() ||
thd->handler_tables_hash.records ||
thd->ull_hash.records ||
thd->global_read_lock.is_acquired());
/*