Optimize flush tables with read lock (FTWRL) to not wait for select's

Part of MDEV-5336 Implement LOCK FOR BACKUP

The idea is that instead of waiting in close_cached_tables() for all
tables to be closed, we instead call flush_tables() that does:
- Flush not used objects in table cache to free memory
- Collect all tables that are open
- Call HA_EXTRA_FLUSH on the objects, to get them into "closed state"
- Added HA_EXTRA_FLUSH support to archive and CSV
- Added multi-user protection to HA_EXTRA_FLUSH in MyISAM and Aria

The benefit compared to old code is:
- FTWRL doesn't have to wait for long running read operations or
  open HANDLER's

1 files changed, 0 insertions, 5 deletions

diff --git a/mysql-test/main/flush.result b/mysql-test/main/flush.result
index af8e327657b..c5176527a3a 100644
--- a/mysql-test/main/flush.result
+++ b/mysql-test/main/flush.result
@@ -472,10 +472,7 @@ create table t1 (i int);
 create table t2 (i int);
 handler t1 open;
 connection con1;
-# Sending:
 flush tables with read lock;
-connection con2;
-# Wait until FTWRL starts waiting for 't1' to be closed.
 connection default;
 # The below statement should not cause deadlock.
 # Sending:
@@ -483,8 +480,6 @@ insert into t2 values (1);
 connection con2;
 # Wait until INSERT starts to wait for FTWRL to go away.
 connection con1;
-# FTWRL should be able to continue now.
-# Reap FTWRL.
 unlock tables;
 connection default;
 # Reap INSERT.