Hi, Sergey!
On Jun 22, Sergey Vojtovich wrote:
> revision-id: 922f9700a7fb084e3f7d6cff56e27e24fc603ed7
> (mariadb-10.2.6-58-g922f970)
> parent(s): 62021f391a42c5577190aa43cb8ad91e56235b46
> committer: Sergey Vojtovich
> timestamp: 2017-06-22 17:35:36 +0400
> message:
>
> MDEV-12882 - Assertion failed in MDL_context::upgrade_shared_lock
>
> Relaxed assertion (in MySQL it was removed).
> For "LOCK TABLES t1 WRITE CONCURRENT, t1 READ" upgrade lock to weakest
> existing suitable lock, which is MDL_SHARED_NO_READ_WRITE.
>
> diff --git a/mysql-test/t/mdl.test b/mysql-test/t/mdl.test
> new file mode 100644
> index 0000000..5a74ae5
> --- /dev/null
> +++ b/mysql-test/t/mdl.test
> @@ -0,0 +1,15 @@
Hm. I'd totally expect main.mdl test to exist for years :)
> diff --git a/sql/sql_parse.cc b/sql/sql_parse.cc
> index 412cd1d..7c910e8 100644
> --- a/sql/sql_parse.cc
> +++ b/sql/sql_parse.cc
> @@ -2787,6 +2787,7 @@ static bool lock_tables_open_and_lock_tables(THD *thd,
> TABLE_LIST *tables)
> ! table->prelocking_placeholder &&
> table->table->file->lock_count() == 0)
> {
> + enum enum_mdl_type lock_type;
> /*
> In case when LOCK TABLE ... READ LOCAL was issued for table with
> storage engine which doesn't support READ LOCAL option and doesn't
> @@ -2799,9 +2800,12 @@ static bool lock_tables_open_and_lock_tables(THD *thd,
> TABLE_LIST *tables)
> deadlock_handler.init();
> thd->push_internal_handler(&deadlock_handler);
>
> + lock_type= table->table->mdl_ticket->get_type() == MDL_SHARED_WRITE ?
> + MDL_SHARED_NO_READ_WRITE : MDL_SHARED_READ_ONLY;
> +
> bool result= thd->mdl_context.upgrade_shared_lock(
> table->table->mdl_ticket,
> - MDL_SHARED_READ_ONLY,
> + lock_type,
> thd->variables.lock_wait_timeout);
This only works if you lock WRITE, then READ. If you do it the other way
around, you'll get an error. Isn't it inconsistent?
Regards,
Sergei
Chief Architect MariaDB
and [email protected]
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