Description:
The MDL_LOCK display of the 'flush table read local' on metadata_locks is different from the actual granted.
The 'flush table read local' execute on innodb engine table get MDL_LOCK process as follow:
At first get the MDL_SHARED_READ, but the innodb is HA_NO_READ_LOCAL_LOCK
so upgrade to MDL_SHARED_READ_ONLY.
But the MDL_context::upgrade_shared_lock only change the type of the ticket,
not change the m_psi of the ticket.
How to repeat:
The test case is as follows：
step 1 on mysql client:
session 1:
create table t1(c1 int, c2 int);
mysql> lock table t1 read local;
mysql> select connection_id();
+-----------------+
| connection_id() |
+-----------------+
| 13 |
+-----------------+
session 2:
mysql> select LOCK_TYPE, LOCK_STATUS from performance_schema.metadata_locks where OBJECT_NAME = 't1'\G
*************************** 1. row ***************************
LOCK_TYPE: SHARED_READ
LOCK_STATUS: GRANTED
+-------------+-------------+
| LOCK_TYPE | LOCK_STATUS |
+-------------+-------------+
| SHARED_READ | GRANTED |
+-------------+-------------+
mysql> select THREAD_OS_ID from performance_schema.threads where PROCESSLIST_ID = 13\G
*************************** 1. row ***************************
THREAD_OS_ID: 8225
step 2 one shell and gdb:
gdb attach 8114 //gdb attach ${mysql_process_pid}
(gdb) info threads
(gdb) thread 37
//switch to the thread execute 'lock table t1 read local'
(gdb) f 11
// switch to the stack do_command.
(gdb) p thd->mdl_context->m_ticket_store.m_durations[2].m_ticket_list->m_first->m_type
$11 = MDL_SHARED_READ_ONLY
(gdb) p (enum enum_mdl_type)((PFS_metadata_lock *) thd->mdl_context->m_ticket_store.m_durations[2].m_ticket_list->m_first->m_psi)->m_mdl_type
$17 = MDL_SHARED_READ
Description: The MDL_LOCK display of the 'flush table read local' on metadata_locks is different from the actual granted. The 'flush table read local' execute on innodb engine table get MDL_LOCK process as follow: At first get the MDL_SHARED_READ, but the innodb is HA_NO_READ_LOCAL_LOCK so upgrade to MDL_SHARED_READ_ONLY. But the MDL_context::upgrade_shared_lock only change the type of the ticket, not change the m_psi of the ticket. How to repeat: The test case is as follows： step 1 on mysql client: session 1: create table t1(c1 int, c2 int); mysql> lock table t1 read local; mysql> select connection_id(); +-----------------+ | connection_id() | +-----------------+ | 13 | +-----------------+ session 2: mysql> select LOCK_TYPE, LOCK_STATUS from performance_schema.metadata_locks where OBJECT_NAME = 't1'\G *************************** 1. row *************************** LOCK_TYPE: SHARED_READ LOCK_STATUS: GRANTED +-------------+-------------+ | LOCK_TYPE | LOCK_STATUS | +-------------+-------------+ | SHARED_READ | GRANTED | +-------------+-------------+ mysql> select THREAD_OS_ID from performance_schema.threads where PROCESSLIST_ID = 13\G *************************** 1. row *************************** THREAD_OS_ID: 8225 step 2 one shell and gdb: gdb attach 8114 //gdb attach ${mysql_process_pid} (gdb) info threads (gdb) thread 37 //switch to the thread execute 'lock table t1 read local' (gdb) f 11 // switch to the stack do_command. (gdb) p thd->mdl_context->m_ticket_store.m_durations[2].m_ticket_list->m_first->m_type $11 = MDL_SHARED_READ_ONLY (gdb) p (enum enum_mdl_type)((PFS_metadata_lock *) thd->mdl_context->m_ticket_store.m_durations[2].m_ticket_list->m_first->m_psi)->m_mdl_type $17 = MDL_SHARED_READ