Bug#40536: SELECT is blocked by INSERT DELAYED waiting on

           upgrading lock, even with low_priority_updates

The problem is that there is no mechanism to control whether a
delayed insert takes a high or low priority lock on a table.

The solution is to modify the delayed insert thread ("handler")
to take into account the global value of low_priority_updates
when taking table locks. The value of low_priority_updates is
retrieved when the insert delayed thread is created and will
remain the same for the duration of the thread.


include/thr_lock.h:
  Update prototype.
mysql-test/r/delayed.result:
  Add test case result for Bug#40536
mysql-test/t/delayed.test:
  Add test case for Bug#40536
mysys/thr_lock.c:
  Add function parameter which specifies the write lock type.
sql/sql_insert.cc:
  Take a low priority write lock if global value of low_priority_updates
  was ON when the thread was created.

1 files changed, 6 insertions, 3 deletions

diff --git a/mysys/thr_lock.c b/mysys/thr_lock.c
index b13e8411771..31638ecee9a 100644
--- a/mysys/thr_lock.c
+++ b/mysys/thr_lock.c
@@ -1359,7 +1359,8 @@ void thr_downgrade_write_lock(THR_LOCK_DATA *in_data,
 
 /* Upgrade a WRITE_DELAY lock to a WRITE_LOCK */
 
-my_bool thr_upgrade_write_delay_lock(THR_LOCK_DATA *data)
+my_bool thr_upgrade_write_delay_lock(THR_LOCK_DATA *data,
+                                     enum thr_lock_type new_lock_type)
 {
   THR_LOCK *lock=data->lock;
   DBUG_ENTER("thr_upgrade_write_delay_lock");
@@ -1372,7 +1373,7 @@ my_bool thr_upgrade_write_delay_lock(THR_LOCK_DATA *data)
   }
   check_locks(lock,"before upgrading lock",0);
   /* TODO:  Upgrade to TL_WRITE_CONCURRENT_INSERT in some cases */
-  data->type=TL_WRITE;				/* Upgrade lock */
+  data->type= new_lock_type;                    /* Upgrade lock */
 
   /* Check if someone has given us the lock */
   if (!data->cond)
@@ -1411,6 +1412,7 @@ my_bool thr_upgrade_write_delay_lock(THR_LOCK_DATA *data)
 my_bool thr_reschedule_write_lock(THR_LOCK_DATA *data)
 {
   THR_LOCK *lock=data->lock;
+  enum thr_lock_type write_lock_type;
   DBUG_ENTER("thr_reschedule_write_lock");
 
   pthread_mutex_lock(&lock->mutex);
@@ -1420,6 +1422,7 @@ my_bool thr_reschedule_write_lock(THR_LOCK_DATA *data)
     DBUG_RETURN(0);
   }
 
+  write_lock_type= data->type;
   data->type=TL_WRITE_DELAYED;
   if (lock->update_status)
     (*lock->update_status)(data->status_param);
@@ -1438,7 +1441,7 @@ my_bool thr_reschedule_write_lock(THR_LOCK_DATA *data)
   free_all_read_locks(lock,0);
 
   pthread_mutex_unlock(&lock->mutex);
-  DBUG_RETURN(thr_upgrade_write_delay_lock(data));
+  DBUG_RETURN(thr_upgrade_write_delay_lock(data, write_lock_type));
 }