Bug#26464 - insert delayed + update + merge = corruption

Using INSERT DELAYED on MERGE tables could lead to table
corruptions.

The manual lists a couple of storage engines, which can be
used with INSERT DELAYED. MERGE is not in this list.

The attempt to try it anyway has not been rejected yet.
This bug was not detected earlier as it can work under
special circumstances. Most notable is low concurrency.

To be safe, this patch rejects any attempt to use INSERT
DELAYED on MERGE tables.


mysql-test/r/merge.result:
  Bug#26464 - insert delayed + update + merge = corruption
  Added test result.
mysql-test/t/merge.test:
  Bug#26464 - insert delayed + update + merge = corruption
  Added test.
sql/ha_myisammrg.h:
  Bug#26464 - insert delayed + update + merge = corruption
  Removed HA_CAN_INSERT_DELAYED flag from table_flags().
  The insert delayed thread upgrades the lock from the first
  entry in MYSQL_LOCK::locks only. Hence it is incapable to
  handle MERGE tables, which have as many entries in this
  array as they have MyISAM sub-tables.

1 files changed, 5 insertions, 0 deletions

diff --git a/mysql-test/r/merge.result b/mysql-test/r/merge.result
index eb333cdadb7..33de735d714 100644
--- a/mysql-test/r/merge.result
+++ b/mysql-test/r/merge.result
@@ -801,3 +801,8 @@ CREATE TABLE tm1(a SMALLINT, b SMALLINT, KEY(a)) ENGINE=MERGE UNION=(t1);
 SELECT * FROM tm1;
 ERROR HY000: Unable to open underlying table which is differently defined or of non-MyISAM type or doesn't exist
 DROP TABLE t1, tm1;
+CREATE TABLE t1(c1 INT) ENGINE=MyISAM;
+CREATE TABLE t2(c1 INT) ENGINE=MERGE UNION=(t1);
+INSERT DELAYED INTO t2 VALUES(1);
+ERROR HY000: Table storage engine for 't2' doesn't have this option
+DROP TABLE t1, t2;