Bug#33756 - query cache with concurrent_insert=0 appears broken

When concurrent inserts were disabled, statements after an INSERT
were not put into the query cache. This happened because we do not
save the current data file length at statement start when
concurrent inserts are disabled. But we checked the always zero
local length against the real file length anyway.
  
Fixed by doing the check only if concurrent inserts are not diabled.


mysql-test/r/query_cache.result:
  Bug#33756 - query cache with concurrent_insert=0 appears broken
  Added test result.
mysql-test/t/query_cache.test:
  Bug#33756 - query cache with concurrent_insert=0 appears broken
  Added test.
sql/ha_myisam.cc:
  Bug#33756 - query cache with concurrent_insert=0 appears broken
  Changed code so that file length check is done only when
  concurrent inserts are possible.

1 files changed, 27 insertions, 0 deletions

diff --git a/mysql-test/r/query_cache.result b/mysql-test/r/query_cache.result
index 68f18d1b0b2..fa80a44c177 100644
--- a/mysql-test/r/query_cache.result
+++ b/mysql-test/r/query_cache.result
@@ -1654,3 +1654,30 @@ set GLOBAL query_cache_type=default;
 set GLOBAL query_cache_limit=default;
 set GLOBAL query_cache_min_res_unit=default;
 set GLOBAL query_cache_size=default;
+use test;
+FLUSH STATUS;
+SET GLOBAL query_cache_size=10*1024*1024;
+SET @save_concurrent_insert= @@concurrent_insert;
+SET GLOBAL concurrent_insert= 0;
+CREATE TABLE t1 (c1 INT NOT NULL) ENGINE=MyISAM;
+INSERT INTO t1 (c1) VALUES (1), (2);
+SHOW GLOBAL VARIABLES LIKE 'concurrent_insert';
+Variable_name	Value
+concurrent_insert	0
+SHOW STATUS LIKE 'Qcache_hits';
+Variable_name	Value
+Qcache_hits	0
+SELECT * FROM t1;
+c1
+1
+2
+SELECT * FROM t1;
+c1
+1
+2
+SHOW STATUS LIKE 'Qcache_hits';
+Variable_name	Value
+Qcache_hits	1
+DROP TABLE t1;
+SET GLOBAL concurrent_insert= @save_concurrent_insert;
+SET GLOBAL query_cache_size= default;