1berry/MariaDB-server
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Bug#39253 Large query cache still freezes server after fix for bug #21074

Browse Source 
This patch introduce a limit on the time the query cache can
block with a lock on SELECTs.

Other operations which causes a change in the table
data will still be blocked.


sql/sql_cache.cc:
  * Introduced a timeout value for the qc lock when entering send_result_to_client()
  and store_query() methods.
sql/sql_cache.h:
  * New signature for Query_cache::try_lock()
This commit is contained in:
Kristofer Pettersson 2009-11-20 13:49:06 +01:00
parent 8369f619d4
commit 41085809c3
2 changed files with 36 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
sql/sql_cache.cc
View File

@ -421,12 +421,16 @@ TYPELIB query_cache_type_typelib=
effect by another thread. This enables a quick path in execution to skip waits
when the outcome is known.
@param use_timeout TRUE if the lock can abort because of a timeout.
@note use_timeout is optional and default value is FALSE.
@return
@retval FALSE An exclusive lock was taken
@retval TRUE The locking attempt failed
*/
bool Query_cache::try_lock(void)
bool Query_cache::try_lock(bool use_timeout)
{
bool interrupt= FALSE;
DBUG_ENTER("Query_cache::try_lock");
@ -456,7 +460,26 @@ bool Query_cache::try_lock(void)
else
{
DBUG_ASSERT(m_cache_lock_status == Query_cache::LOCKED);
pthread_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
/*
To prevent send_result_to_client() and query_cache_insert() from
blocking execution for too long a timeout is put on the lock.
*/
if (use_timeout)
{
struct timespec waittime;
set_timespec_nsec(waittime,(ulong)(50000000L)); /* Wait for 50 msec */
int res= pthread_cond_timedwait(&COND_cache_status_changed,
&structure_guard_mutex,&waittime);
if (res == ETIMEDOUT)
{
interrupt= TRUE;
break;
}
}
else
{
pthread_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
}
}
}
pthread_mutex_unlock(&structure_guard_mutex);
@ -1190,8 +1213,14 @@ def_week_frmt: %lu, in_trans: %d, autocommit: %d",
A table- or a full flush operation can potentially take a long time to
finish. We choose not to wait for them and skip caching statements
instead.
In case the wait time can't be determined there is an upper limit which
causes try_lock() to abort with a time out.
The 'TRUE' parameter indicate that the lock is allowed to timeout
*/
if (try_lock())
if (try_lock(TRUE))
DBUG_VOID_RETURN;
if (query_cache_size == 0)
{
@ -1385,8 +1414,10 @@ Query_cache::send_result_to_client(THD *thd, char *sql, uint query_length)
Try to obtain an exclusive lock on the query cache. If the cache is
disabled or if a full cache flush is in progress, the attempt to
get the lock is aborted.
The 'TRUE' parameter indicate that the lock is allowed to timeout
*/
if (try_lock())
if (try_lock(TRUE))
goto err;
if (query_cache_size == 0)

2
sql/sql_cache.h
View File

@ -485,7 +485,7 @@ protected:
const char *name);
my_bool in_blocks(Query_cache_block * point);
bool try_lock(void);
bool try_lock(bool use_timeout= FALSE);
void lock(void);
void lock_and_suspend(void);
void unlock(void);