MDEV-5492 - Reduce usage of LOCK_open: TABLE::in_use

Move TABLE::in_use out of LOCK_open.

This is done with assumtion that foreign threads accessing TABLE::in_use
will only need consistent value _after_ marking table for flush and purging
unused table instances. In this case TABLE::in_use will always point to a
valid thread object.

Previously FLUSH TABLES thread may wait for tables flushed subsequently by
concurrent threads which breaks the above assumption, e.g.:
open tables: t1 (version= 1)
thr1 (FLUSH TABLES): refresh_version++
thr1 (FLUSH TABLES): purge table cache
open tables: none
thr2 (SELECT * FROM t1): open tables: t1
open tables: t1 (version= 2)
thr2 (FLUSH TABLES): refresh_version++
thr2 (FLUSH TABLES): purge table cache
thr1 (FLUSH TABLES): wait for old tables (including t1 with version 2)

It is fixed so that FLUSH TABLES waits only for tables that were open
heretofore.

1 files changed, 1 insertions, 1 deletions

diff --git a/sql/sql_handler.cc b/sql/sql_handler.cc
index 812a5dc1461..6b961ac2262 100644
--- a/sql/sql_handler.cc
+++ b/sql/sql_handler.cc
@@ -1135,7 +1135,7 @@ void mysql_ha_flush(THD *thd)
         ((hash_tables->table->mdl_ticket &&
          hash_tables->table->mdl_ticket->has_pending_conflicting_lock()) ||
          (!hash_tables->table->s->tmp_table &&
-          hash_tables->table->s->has_old_version())))
+          hash_tables->table->s->tdc.flushed)))
       mysql_ha_close_table(hash_tables);
   }