[MDEV-21281] main.backup_interaction fails intermittently - Jira

The following intermittent result difference was observed immediately after ~~MDEV-16678~~ was pushed to 10.5.

CURRENT_TEST: main.backup_interaction

--- /usr/share/mysql/mysql-test/main/backup_interaction.result	2019-12-10 14:25:41.000000000 -0500

+++ /dev/shm/var/4/log/backup_interaction.reject	2019-12-10 16:16:44.997159774 -0500

@@ -105,6 +105,7 @@

 select lock_mode from information_schema.metadata_lock_info;

 lock_mode

 MDL_BACKUP_START

+MDL_SHARED

 backup stage block_commit;

 commit;

 backup stage end;

I am able to repeat it locally:

10.5 adb117cf6901a0e0da7577267be1209359892207
main.backup_interaction 'innodb' w6 [ 7 fail ]
Test ended at 2019-12-11 09:15:35

CURRENT_TEST: main.backup_interaction
--- /mariadb/10.5/mysql-test/main/backup_interaction.result 2019-10-28 17:09:53.002690675 +0200
+++ /mariadb/10.5/mysql-test/main/backup_interaction.reject 2019-12-11 09:15:35.661386904 +0200
@@ -105,6 +105,7 @@
select lock_mode from information_schema.metadata_lock_info;
lock_mode
MDL_BACKUP_START
+MDL_SHARED
backup stage block_commit;
commit;
backup stage end;

This was an optimized ASAN debug build with

ASAN_OPTIONS=abort_on_error=1 ./mtr --repeat=100 --parallel=auto main.backup_interaction{,,,,,,,,,,,}

relates to

MDEV-16678 Use MDL for innodb background threads instead of dict_operation_lock

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