#At file:///Users/thek/Development/51-bug43758-2/ based on revid:patrick.crews@stripped
2937 Kristofer Pettersson 2009-06-15
Bug#43758 Query cache can lock up threads in 'freeing items' state
Early patch submitted for discussion.
It is possible for more than one thread to enter the condition
in query_cache_insert(), but the condition predicate is to
signal one thread each time the cache status changes between
the following states: {NO_FLUSH_IN_PROGRESS,FLUSH_IN_PROGRESS,
TABLE_FLUSH_IN_PROGRESS}
Consider three threads THD1, THD2, THD3
THD2: select ... => Got a writer in ::store_query
THD3: select ... => Got a writer in ::store_query
THD1: flush tables => qc status= FLUSH_IN_PROGRESS;
new writers are blocked.
THD2: select ... => Still got a writer and enters cond in
query_cache_insert
THD3: select ... => Still got a writer and enters cond in
query_cache_insert
THD1: flush tables => finished and signal status change.
THD2: select ... => Wakes up and completes the insert.
THD3: select ... => Happily waiting for better times. Why hurry?
This patch is a refactoring of this lock system. It introduces tree new methods:
try_lock_query_cache()
lock_quey_cache()
unlock_query_cache()
This change also makes wait_while_table_flush_is_in_progress(). All threads are
queued and put on a conditional wait. On each unlock the queue is signalled. This resolve
the issues with missing signals. To assure that no threads are spending unnecessary
time waiting a signal broad cast is issued every time a lock is taken before a full
cache flush.
@ mysql-test/r/query_cache_debug.result
* Added test case for bug43758
@ mysql-test/t/query_cache_debug.test
* Added test case for bug43758
@ sql/sql_cache.cc
* Replaced calls to wait_while_table_flush_is_in_progress() with
calls to try_lock(), lock_and_suspend() and unlock().
* Renamed enumeration Cache_status to Cache_lock_status.
* Renamed enumeration items to UNLOCKED, LOCKED_NO_WAIT and LOCKED.
If the LOCKED_NO_WAIT lock type is used to lock the query cache, other
threads using try_lock() will fail to acquire the lock.
This is useful if the query cache is temporary disabled due to
a full table flush.
@ sql/sql_cache.h
* Replaced calls to wait_while_table_flush_is_in_progress() with
calls to try_lock(), lock_and_suspend() and unlock().
* Renamed enumeration Cache_status to Cache_lock_status.
* Renamed enumeration items to UNLOCKED, LOCKED_NO_WAIT and LOCKED.
If the LOCKED_NO_WAIT lock type is used to lock the query cache, other
threads using try_lock() will fail to acquire the lock.
This is useful if the query cache is temporary disabled due to
a full table flush.
modified:
mysql-test/r/query_cache_debug.result
mysql-test/t/query_cache_debug.test
sql/sql_cache.cc
sql/sql_cache.h
=== modified file 'mysql-test/r/query_cache_debug.result'
--- a/mysql-test/r/query_cache_debug.result 2009-02-19 21:09:35 +0000
+++ b/mysql-test/r/query_cache_debug.result 2009-06-15 14:55:52 +0000
@@ -71,3 +71,111 @@ DROP TABLE t1,t2;
SET GLOBAL concurrent_insert= DEFAULT;
SET GLOBAL query_cache_size= DEFAULT;
SET GLOBAL query_cache_type= DEFAULT;
+#
+# Bug43758 Query cache can lock up threads in 'freeing items' state
+#
+FLUSH STATUS;
+SET GLOBAL query_cache_type=DEMAND;
+SET GLOBAL query_cache_size= 1024*768;
+DROP TABLE IF EXISTS t1,t2,t3,t4,t5;
+CREATE TABLE t1 (a VARCHAR(100));
+CREATE TABLE t2 (a VARCHAR(100));
+CREATE TABLE t3 (a VARCHAR(100));
+CREATE TABLE t4 (a VARCHAR(100));
+CREATE TABLE t5 (a VARCHAR(100));
+INSERT INTO t1 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+INSERT INTO t2 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+INSERT INTO t3 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+INSERT INTO t4 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+INSERT INTO t5 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+=================================== Connection thd1
+**
+** Load Query Cache with a result set and one table.
+**
+SELECT SQL_CACHE * FROM t1;
+a
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
+*************************************************************************
+** We want to accomplish the following state:
+** - Query cache status: TABLE_FLUSH_IN_PROGRESS
+** - THD1: invalidate_table_internal (iterating query blocks)
+** - THD2: query_cache_insert (cond_wait)
+** - THD3: query_cache_insert (cond_wait)
+** - No thread should be holding the structure_guard_mutex.
+**
+** First step is to place a DELETE-statement on the debug hook just
+** before the mutex lock in invalidate_table_internal.
+** This will allow new result sets to be written into the QC.
+**
+SET SESSION debug='+d,wait_in_query_cache_invalidate1';
+SET SESSION debug='+d,wait_in_query_cache_invalidate2';
+DELETE FROM t1 WHERE a like '%a%';;
+=================================== Connection default
+** Assert that the expect process status is obtained.
+**
+=================================== Connection thd2
+** On THD2: Insert a result into the cache. This attempt will be blocked
+** because of a debug hook placed just before the mutex lock after which
+** the first part of the result set is written.
+SET SESSION debug='+d,wait_in_query_cache_insert';
+SELECT SQL_CACHE * FROM t2 UNION SELECT * FROM t3;
+=================================== Connection thd3
+** On THD3: Insert another result into the cache and block on the same
+** debug hook.
+SET SESSION debug='+d,wait_in_query_cache_insert';
+SELECT SQL_CACHE * FROM t4 UNION SELECT * FROM t5;;
+=================================== Connection default
+** Assert that the two SELECT-stmt threads to reach the hook.
+**
+**
+** Signal the DELETE thread, THD1, to continue. It will enter the mutex
+** lock and set query cache status to TABLE_FLUSH_IN_PROGRESS and then
+** unlock the mutex before stopping on the next debug hook.
+SELECT SQL_NO_CACHE id FROM information_schema.processlist WHERE state='wait_in_query_cache_invalidate1' LIMIT 1 INTO @flush_thread_id;
+KILL QUERY @flush_thread_id;
+** Assert that we reach the next debug hook.
+**
+** Signal the remaining debug hooks blocking THD2 and THD3.
+** The threads will grab the guard mutex enter the wait condition and
+** and finally release the mutex. The threads will continue to wait
+** until a broadcast signal reaches them causing both threads to
+** come alive and check the condition.
+SELECT SQL_NO_CACHE id FROM information_schema.processlist WHERE state='wait_in_query_cache_insert' LIMIT 1 INTO @thread_id;
+KILL QUERY @thread_id;
+SELECT SQL_NO_CACHE id FROM information_schema.processlist WHERE state='wait_in_query_cache_insert' LIMIT 1 INTO @thread_id;
+KILL QUERY @thread_id;
+**
+** Finally signal the DELETE statement on THD1 one last time.
+** The stmt will complete the query cache invalidation and return
+** cache status to NO_FLUSH_IN_PROGRESS. On the status change
+** One signal will be sent to the thread group waiting for executing
+** invalidations and a broadcast signal will be sent to the thread
+** group holding result set writers.
+SELECT SQL_NO_CACHE id FROM information_schema.processlist WHERE state='wait_in_query_cache_invalidate2' LIMIT 1 INTO @flush_thread_id;
+KILL QUERY @flush_thread_id;
+**
+*************************************************************************
+** No tables should be locked
+=================================== Connection thd2
+a
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
+DELETE FROM t1;
+DELETE FROM t2;
+DELETE FROM t3;
+=================================== Connection thd3
+a
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
+DELETE FROM t4;
+DELETE FROM t5;
+=================================== Connection thd1
+** Done.
+SET GLOBAL query_cache_size= 0;
+# Restore defaults
+RESET QUERY CACHE;
+FLUSH STATUS;
+DROP TABLE t1,t2,t3,t4,t5;
+SET GLOBAL query_cache_size= DEFAULT;
+SET GLOBAL query_cache_type= DEFAULT;
=== modified file 'mysql-test/t/query_cache_debug.test'
--- a/mysql-test/t/query_cache_debug.test 2009-02-19 21:09:35 +0000
+++ b/mysql-test/t/query_cache_debug.test 2009-06-15 14:55:52 +0000
@@ -112,3 +112,147 @@ DROP TABLE t1,t2;
SET GLOBAL concurrent_insert= DEFAULT;
SET GLOBAL query_cache_size= DEFAULT;
SET GLOBAL query_cache_type= DEFAULT;
+
+
+--echo #
+--echo # Bug43758 Query cache can lock up threads in 'freeing items' state
+--echo #
+FLUSH STATUS;
+SET GLOBAL query_cache_type=DEMAND;
+SET GLOBAL query_cache_size= 1024*768;
+--disable_warnings
+DROP TABLE IF EXISTS t1,t2,t3,t4,t5;
+--enable_warnings
+CREATE TABLE t1 (a VARCHAR(100));
+CREATE TABLE t2 (a VARCHAR(100));
+CREATE TABLE t3 (a VARCHAR(100));
+CREATE TABLE t4 (a VARCHAR(100));
+CREATE TABLE t5 (a VARCHAR(100));
+
+INSERT INTO t1 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+INSERT INTO t2 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+INSERT INTO t3 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+INSERT INTO t4 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+INSERT INTO t5 VALUES ('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'),('bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb');
+
+connect (thd2, localhost, root, ,test);
+connect (thd3, localhost, root, ,test);
+connect (thd1, localhost, root, ,test);
+
+connection thd1;
+--echo =================================== Connection thd1
+--echo **
+--echo ** Load Query Cache with a result set and one table.
+--echo **
+SELECT SQL_CACHE * FROM t1;
+--echo *************************************************************************
+--echo ** We want to accomplish the following state:
+--echo ** - Query cache status: TABLE_FLUSH_IN_PROGRESS
+--echo ** - THD1: invalidate_table_internal (iterating query blocks)
+--echo ** - THD2: query_cache_insert (cond_wait)
+--echo ** - THD3: query_cache_insert (cond_wait)
+--echo ** - No thread should be holding the structure_guard_mutex.
+--echo **
+--echo ** First step is to place a DELETE-statement on the debug hook just
+--echo ** before the mutex lock in invalidate_table_internal.
+--echo ** This will allow new result sets to be written into the QC.
+--echo **
+SET SESSION debug='+d,wait_in_query_cache_invalidate1';
+SET SESSION debug='+d,wait_in_query_cache_invalidate2';
+--send DELETE FROM t1 WHERE a like '%a%';
+
+connection default;
+--echo =================================== Connection default
+--echo ** Assert that the expect process status is obtained.
+LET $wait_condition= SELECT SQL_NO_CACHE COUNT(*)= 1 FROM information_schema.processlist WHERE state= 'wait_in_query_cache_invalidate1';
+--source include/wait_condition.inc
+-- echo **
+
+connection thd2;
+--echo =================================== Connection thd2
+--echo ** On THD2: Insert a result into the cache. This attempt will be blocked
+--echo ** because of a debug hook placed just before the mutex lock after which
+--echo ** the first part of the result set is written.
+SET SESSION debug='+d,wait_in_query_cache_insert';
+--send SELECT SQL_CACHE * FROM t2 UNION SELECT * FROM t3
+
+connection thd3;
+--echo =================================== Connection thd3
+--echo ** On THD3: Insert another result into the cache and block on the same
+--echo ** debug hook.
+SET SESSION debug='+d,wait_in_query_cache_insert';
+--send SELECT SQL_CACHE * FROM t4 UNION SELECT * FROM t5;
+
+connection default;
+--echo =================================== Connection default
+--echo ** Assert that the two SELECT-stmt threads to reach the hook.
+LET $wait_condition= SELECT SQL_NO_CACHE COUNT(*)= 2 FROM information_schema.processlist WHERE state='wait_in_query_cache_insert';
+--source include/wait_condition.inc
+--echo **
+--echo **
+
+--echo ** Signal the DELETE thread, THD1, to continue. It will enter the mutex
+--echo ** lock and set query cache status to TABLE_FLUSH_IN_PROGRESS and then
+--echo ** unlock the mutex before stopping on the next debug hook.
+SELECT SQL_NO_CACHE id FROM information_schema.processlist WHERE state='wait_in_query_cache_invalidate1' LIMIT 1 INTO @flush_thread_id;
+KILL QUERY @flush_thread_id;
+--echo ** Assert that we reach the next debug hook.
+LET $wait_condition= SELECT SQL_NO_CACHE COUNT(*)= 1 FROM information_schema.processlist WHERE state='wait_in_query_cache_invalidate2';
+--source include/wait_condition.inc
+
+--echo **
+--echo ** Signal the remaining debug hooks blocking THD2 and THD3.
+--echo ** The threads will grab the guard mutex enter the wait condition and
+--echo ** and finally release the mutex. The threads will continue to wait
+--echo ** until a broadcast signal reaches them causing both threads to
+--echo ** come alive and check the condition.
+SELECT SQL_NO_CACHE id FROM information_schema.processlist WHERE state='wait_in_query_cache_insert' LIMIT 1 INTO @thread_id;
+KILL QUERY @thread_id;
+SELECT SQL_NO_CACHE id FROM information_schema.processlist WHERE state='wait_in_query_cache_insert' LIMIT 1 INTO @thread_id;
+KILL QUERY @thread_id;
+--echo **
+--echo ** Finally signal the DELETE statement on THD1 one last time.
+--echo ** The stmt will complete the query cache invalidation and return
+--echo ** cache status to NO_FLUSH_IN_PROGRESS. On the status change
+--echo ** One signal will be sent to the thread group waiting for executing
+--echo ** invalidations and a broadcast signal will be sent to the thread
+--echo ** group holding result set writers.
+SELECT SQL_NO_CACHE id FROM information_schema.processlist WHERE state='wait_in_query_cache_invalidate2' LIMIT 1 INTO @flush_thread_id;
+KILL QUERY @flush_thread_id;
+
+--echo **
+--echo *************************************************************************
+--echo ** No tables should be locked
+connection thd2;
+--echo =================================== Connection thd2
+reap;
+DELETE FROM t1;
+DELETE FROM t2;
+DELETE FROM t3;
+
+connection thd3;
+--echo =================================== Connection thd3
+reap;
+DELETE FROM t4;
+DELETE FROM t5;
+
+connection thd1;
+--echo =================================== Connection thd1
+reap;
+
+--echo ** Done.
+
+connection default;
+disconnect thd1;
+disconnect thd2;
+disconnect thd3;
+SET GLOBAL query_cache_size= 0;
+
+connection default;
+--echo # Restore defaults
+RESET QUERY CACHE;
+FLUSH STATUS;
+DROP TABLE t1,t2,t3,t4,t5;
+SET GLOBAL query_cache_size= DEFAULT;
+SET GLOBAL query_cache_type= DEFAULT;
+exit;
=== modified file 'sql/sql_cache.cc'
--- a/sql/sql_cache.cc 2009-05-15 12:57:51 +0000
+++ b/sql/sql_cache.cc 2009-06-15 14:55:52 +0000
@@ -420,6 +420,102 @@ TYPELIB query_cache_type_typelib=
/**
+ Serialize access to the query cache.
+
+ @return
+ @retval FALSE An exclusive lock was taken
+ @retval TRUE The locking attempt failed
+*/
+
+bool Query_cache::try_lock(void)
+{
+ bool interrupt= FALSE;
+ DBUG_ENTER("Query_cache::try_lock");
+
+ pthread_mutex_lock(&structure_guard_mutex);
+ while (1)
+ {
+ if (m_cache_lock_status == Query_cache::UNLOCKED)
+ {
+ m_cache_lock_status= Query_cache::LOCKED;
+#ifndef DBUG_OFF
+ THD *thd= current_thd;
+ if (thd)
+ m_cache_lock_thread_id= thd->thread_id;
+#endif
+ break;
+ }
+ else if (m_cache_lock_status == Query_cache::LOCKED_NO_WAIT)
+ {
+ /*
+ If query cache is protected by a LOCKED_NO_WAIT lock this thread
+ should avoid using the query cache as it is being evicted.
+ */
+ interrupt= TRUE;
+ break;
+ }
+ else
+ {
+ DBUG_ASSERT(m_cache_lock_status == Query_cache::LOCKED);
+ pthread_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
+ }
+ }
+ pthread_mutex_unlock(&structure_guard_mutex);
+
+ DBUG_RETURN(interrupt);
+}
+
+
+/**
+ Serialize access to the query cache.
+ @param lock_type LOCKED or SUSPENDING
+
+ The lock type affects other threads using try_lock(). If the
+ lock_type is SUSPENDING then try_lock() will fail. This lock_type
+ is used if the query cache is undergoing a full cache flush.
+ */
+
+void Query_cache::lock_and_suspend(void)
+{
+ DBUG_ENTER("Query_cache::lock_and_suspend");
+
+ pthread_mutex_lock(&structure_guard_mutex);
+ while (m_cache_lock_status != Query_cache::UNLOCKED)
+ pthread_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
+ m_cache_lock_status= Query_cache::LOCKED_NO_WAIT;
+#ifndef DBUG_OFF
+ THD *thd= current_thd;
+ if (thd)
+ m_cache_lock_thread_id= thd->thread_id;
+#endif
+ /* Wake up everybody, a whole cache flush is starting! */
+ pthread_cond_broadcast(&COND_cache_status_changed);
+ pthread_mutex_unlock(&structure_guard_mutex);
+
+ DBUG_VOID_RETURN;
+}
+
+
+void Query_cache::unlock(void)
+{
+ DBUG_ENTER("Query_cache::unlock");
+ pthread_mutex_lock(&structure_guard_mutex);
+#ifndef DBUG_OFF
+ THD *thd= current_thd;
+ if (thd)
+ DBUG_ASSERT(m_cache_lock_thread_id == thd->thread_id);
+#endif
+ DBUG_ASSERT(m_cache_lock_status == Query_cache::LOCKED ||
+ m_cache_lock_status == Query_cache::LOCKED_NO_WAIT);
+ m_cache_lock_status= Query_cache::UNLOCKED;
+ DBUG_PRINT("Query_cache",("Sending signal"));
+ pthread_cond_signal(&COND_cache_status_changed);
+ pthread_mutex_unlock(&structure_guard_mutex);
+ DBUG_VOID_RETURN;
+}
+
+
+/**
Helper function for determine if a SELECT statement has a SQL_NO_CACHE
directive.
@@ -713,14 +809,8 @@ void query_cache_insert(NET *net, const
DBUG_EXECUTE_IF("wait_in_query_cache_insert",
debug_wait_for_kill("wait_in_query_cache_insert"); );
- STRUCT_LOCK(&query_cache.structure_guard_mutex);
- bool interrupt;
- query_cache.wait_while_table_flush_is_in_progress(&interrupt);
- if (interrupt)
- {
- STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+ if (query_cache.try_lock())
DBUG_VOID_RETURN;
- }
Query_cache_block *query_block= (Query_cache_block*)net->query_cache_query;
if (!query_block)
@@ -729,7 +819,7 @@ void query_cache_insert(NET *net, const
We lost the writer and the currently processed query has been
invalidated; there is nothing left to do.
*/
- STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+ query_cache.unlock();
DBUG_VOID_RETURN;
}
@@ -755,7 +845,7 @@ void query_cache_insert(NET *net, const
query_cache.free_query(query_block);
query_cache.refused++;
// append_result_data no success => we need unlock
- STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+ query_cache.unlock();
DBUG_VOID_RETURN;
}
@@ -777,14 +867,8 @@ void query_cache_abort(NET *net)
if (net->query_cache_query == 0)
DBUG_VOID_RETURN;
- STRUCT_LOCK(&query_cache.structure_guard_mutex);
- bool interrupt;
- query_cache.wait_while_table_flush_is_in_progress(&interrupt);
- if (interrupt)
- {
- STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+ if (query_cache.try_lock())
DBUG_VOID_RETURN;
- }
/*
While we were waiting another thread might have changed the status
@@ -803,8 +887,7 @@ void query_cache_abort(NET *net)
DBUG_EXECUTE("check_querycache",query_cache.check_integrity(1););
}
- STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
-
+ query_cache.unlock();
DBUG_VOID_RETURN;
}
@@ -832,15 +915,8 @@ void query_cache_end_of_result(THD *thd)
emb_count_querycache_size(thd));
#endif
- STRUCT_LOCK(&query_cache.structure_guard_mutex);
-
- bool interrupt;
- query_cache.wait_while_table_flush_is_in_progress(&interrupt);
- if (interrupt)
- {
- STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+ if (query_cache.try_lock())
DBUG_VOID_RETURN;
- }
query_block= ((Query_cache_block*) thd->net.query_cache_query);
if (query_block)
@@ -869,10 +945,9 @@ void query_cache_end_of_result(THD *thd)
*/
DBUG_ASSERT(0);
query_cache.free_query(query_block);
- STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+ query_cache.unlock();
DBUG_VOID_RETURN;
}
-
last_result_block= header->result()->prev;
allign_size= ALIGN_SIZE(last_result_block->used);
len= max(query_cache.min_allocation_unit, allign_size);
@@ -885,13 +960,11 @@ void query_cache_end_of_result(THD *thd)
/* Drop the writer. */
header->writer(0);
thd->net.query_cache_query= 0;
-
BLOCK_UNLOCK_WR(query_block);
DBUG_EXECUTE("check_querycache",query_cache.check_integrity(1););
}
-
- STRUCT_UNLOCK(&query_cache.structure_guard_mutex);
+ query_cache.unlock();
DBUG_VOID_RETURN;
}
@@ -950,11 +1023,7 @@ ulong Query_cache::resize(ulong query_ca
query_cache_size_arg));
DBUG_ASSERT(initialized);
- STRUCT_LOCK(&structure_guard_mutex);
- while (is_flushing())
- pthread_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
- m_cache_status= Query_cache::FLUSH_IN_PROGRESS;
- STRUCT_UNLOCK(&structure_guard_mutex);
+ lock_and_suspend();
/*
Wait for all readers and writers to exit. When the list of all queries
@@ -986,13 +1055,10 @@ ulong Query_cache::resize(ulong query_ca
query_cache_size= query_cache_size_arg;
new_query_cache_size= init_cache();
- STRUCT_LOCK(&structure_guard_mutex);
- m_cache_status= Query_cache::NO_FLUSH_IN_PROGRESS;
- pthread_cond_signal(&COND_cache_status_changed);
if (new_query_cache_size)
DBUG_EXECUTE("check_querycache",check_integrity(1););
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_RETURN(new_query_cache_size);
}
@@ -1089,15 +1155,16 @@ def_week_frmt: %lu, in_trans: %d, autoco
*/
ha_release_temporary_latches(thd);
- STRUCT_LOCK(&structure_guard_mutex);
- if (query_cache_size == 0 || is_flushing())
+ /*
+ 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.
+ */
+ if (try_lock())
+ DBUG_VOID_RETURN;
+ if (query_cache_size == 0)
{
- /*
- 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.
- */
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_VOID_RETURN;
}
DUMP(this);
@@ -1105,7 +1172,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
if (ask_handler_allowance(thd, tables_used))
{
refused++;
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_VOID_RETURN;
}
@@ -1153,7 +1220,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
DBUG_PRINT("qcache", ("insertion in query hash"));
header->unlock_n_destroy();
free_memory_block(query_block);
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
goto end;
}
if (!register_all_tables(query_block, tables_used, local_tables))
@@ -1163,7 +1230,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
hash_delete(&queries, (uchar *) query_block);
header->unlock_n_destroy();
free_memory_block(query_block);
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
goto end;
}
double_linked_list_simple_include(query_block, &queries_blocks);
@@ -1173,7 +1240,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
header->writer(net);
header->tables_type(tables_type);
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
// init_n_lock make query block locked
BLOCK_UNLOCK_WR(query_block);
@@ -1182,7 +1249,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
{
// We have not enough memory to store query => do nothing
refused++;
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_PRINT("warning", ("Can't allocate query"));
}
}
@@ -1190,7 +1257,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
{
// Another thread is processing the same query => do nothing
refused++;
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_PRINT("qcache", ("Another thread process same query"));
}
}
@@ -1282,18 +1349,17 @@ Query_cache::send_result_to_client(THD *
}
}
- STRUCT_LOCK(&structure_guard_mutex);
+ /*
+ 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.
+ */
+ if (try_lock())
+ goto err;
if (query_cache_size == 0)
goto err_unlock;
- if (is_flushing())
- {
- /* Return; Query cache is temporarily disabled while we flush. */
- DBUG_PRINT("qcache",("query cache disabled"));
- goto err_unlock;
- }
-
/*
Check that we haven't forgot to reset the query cache variables;
make sure there are no attached query cache writer to this thread.
@@ -1427,7 +1493,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
DBUG_PRINT("qcache",
("Temporary table detected: '%s.%s'",
table_list.db, table_list.alias));
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
/*
We should not store result of this query because it contain
temporary tables => assign following variable to make check
@@ -1448,7 +1514,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
DBUG_PRINT("qcache",
("probably no SELECT access to %s.%s => return to normal processing",
table_list.db, table_list.alias));
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
thd->lex->safe_to_cache_query=0; // Don't try to cache this
BLOCK_UNLOCK_RD(query_block);
DBUG_RETURN(-1); // Privilege error
@@ -1491,7 +1557,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
}
move_to_query_list_end(query_block);
hits++;
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
/*
Send cached result to client
@@ -1530,7 +1596,7 @@ def_week_frmt: %lu, in_trans: %d, autoco
DBUG_RETURN(1); // Result sent to client
err_unlock:
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
err:
DBUG_RETURN(0); // Query was not cached
}
@@ -1651,47 +1717,6 @@ void Query_cache::invalidate(THD *thd, c
/**
- Synchronize the thread with any flushing operations.
-
- This helper function is called whenever a thread needs to operate on the
- query cache structure (example: during invalidation). If a table flush is in
- progress this function will wait for it to stop. If a full flush is in
- progress, the function will set the interrupt parameter to indicate that the
- current operation is redundant and should be interrupted.
-
- @param[out] interrupt This out-parameter will be set to TRUE if the calling
- function is redundant and should be interrupted.
-
- @return If the interrupt-parameter is TRUE then m_cache_status is set to
- NO_FLUSH_IN_PROGRESS. If the interrupt-parameter is FALSE then
- m_cache_status is set to FLUSH_IN_PROGRESS.
- The structure_guard_mutex will in any case be locked.
-*/
-
-void Query_cache::wait_while_table_flush_is_in_progress(bool *interrupt)
-{
- while (is_flushing())
- {
- /*
- If there already is a full flush in progress query cache isn't enabled
- and additional flushes are redundant; just return instead.
- */
- if (m_cache_status == Query_cache::FLUSH_IN_PROGRESS)
- {
- *interrupt= TRUE;
- return;
- }
- /*
- If a table flush is in progress; wait on cache status to change.
- */
- if (m_cache_status == Query_cache::TABLE_FLUSH_IN_PROGRESS)
- pthread_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
- }
- *interrupt= FALSE;
-}
-
-
-/**
Remove all cached queries that uses the given database.
*/
@@ -1700,14 +1725,13 @@ void Query_cache::invalidate(char *db)
bool restart= FALSE;
DBUG_ENTER("Query_cache::invalidate (db)");
- STRUCT_LOCK(&structure_guard_mutex);
- bool interrupt;
- wait_while_table_flush_is_in_progress(&interrupt);
- if (interrupt)
- {
- STRUCT_UNLOCK(&structure_guard_mutex);
- return;
- }
+ /*
+ try_lock is a blocking attempt to get a lock.
+ If a lock can't be obtained it is because the cache is either disabled or
+ it is being flushed.
+ */
+ if (try_lock())
+ DBUG_VOID_RETURN;
THD *thd= current_thd;
@@ -1763,7 +1787,7 @@ void Query_cache::invalidate(char *db)
} while (restart);
} // end if( tables_blocks )
}
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_VOID_RETURN;
}
@@ -1787,7 +1811,10 @@ void Query_cache::invalidate_by_MyISAM_f
void Query_cache::flush()
{
DBUG_ENTER("Query_cache::flush");
- STRUCT_LOCK(&structure_guard_mutex);
+ DBUG_EXECUTE_IF("wait_in_query_cache_flush1",
+ debug_wait_for_kill("wait_in_query_cache_flush1"););
+
+ lock_and_suspend();
if (query_cache_size > 0)
{
DUMP(this);
@@ -1796,7 +1823,7 @@ void Query_cache::flush()
}
DBUG_EXECUTE("check_querycache",query_cache.check_integrity(1););
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_VOID_RETURN;
}
@@ -1815,18 +1842,12 @@ void Query_cache::pack(ulong join_limit,
{
DBUG_ENTER("Query_cache::pack");
- bool interrupt;
- STRUCT_LOCK(&structure_guard_mutex);
- wait_while_table_flush_is_in_progress(&interrupt);
- if (interrupt)
- {
- STRUCT_UNLOCK(&structure_guard_mutex);
- DBUG_VOID_RETURN;
- }
+ lock_and_suspend();
+
if (query_cache_size == 0)
{
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_VOID_RETURN;
}
@@ -1836,7 +1857,7 @@ void Query_cache::pack(ulong join_limit,
pack_cache();
} while ((++i < iteration_limit) && join_results(join_limit));
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_VOID_RETURN;
}
@@ -1851,9 +1872,9 @@ void Query_cache::destroy()
else
{
/* Underlying code expects the lock. */
- STRUCT_LOCK(&structure_guard_mutex);
+ lock_and_suspend();
free_cache();
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
pthread_cond_destroy(&COND_cache_status_changed);
pthread_mutex_destroy(&structure_guard_mutex);
@@ -1872,7 +1893,7 @@ void Query_cache::init()
DBUG_ENTER("Query_cache::init");
pthread_mutex_init(&structure_guard_mutex,MY_MUTEX_INIT_FAST);
pthread_cond_init(&COND_cache_status_changed, NULL);
- m_cache_status= Query_cache::NO_FLUSH_IN_PROGRESS;
+ m_cache_lock_status= Query_cache::UNLOCKED;
initialized = 1;
DBUG_VOID_RETURN;
}
@@ -2112,23 +2133,9 @@ void Query_cache::free_cache()
void Query_cache::flush_cache()
{
- /*
- If there is flush in progress, wait for it to finish, and then do
- our flush. This is necessary because something could be added to
- the cache before we acquire the lock again, and some code (like
- Query_cache::free_cache()) depends on the fact that after the
- flush the cache is empty.
- */
- while (is_flushing())
- pthread_cond_wait(&COND_cache_status_changed, &structure_guard_mutex);
-
- /*
- Setting 'FLUSH_IN_PROGRESS' will prevent other threads from using
- the cache while we are in the middle of the flush, and we release
- the lock so that other threads won't block.
- */
- m_cache_status= Query_cache::FLUSH_IN_PROGRESS;
- STRUCT_UNLOCK(&structure_guard_mutex);
+
+ DBUG_EXECUTE_IF("wait_in_query_cache_flush2",
+ debug_wait_for_kill("wait_in_query_cache_flush2"););
my_hash_reset(&queries);
while (queries_blocks != 0)
@@ -2136,10 +2143,6 @@ void Query_cache::flush_cache()
BLOCK_LOCK_WR(queries_blocks);
free_query_internal(queries_blocks);
}
-
- STRUCT_LOCK(&structure_guard_mutex);
- m_cache_status= Query_cache::NO_FLUSH_IN_PROGRESS;
- pthread_cond_signal(&COND_cache_status_changed);
}
/*
@@ -2394,7 +2397,7 @@ Query_cache::append_result_data(Query_ca
else
{
// It is success (nobody can prevent us write data)
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
}
// Now finally write data to the last block
@@ -2432,7 +2435,7 @@ my_bool Query_cache::write_result_data(Q
if (success)
{
// It is success (nobody can prevent us write data)
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
uint headers_len = (ALIGN_SIZE(sizeof(Query_cache_block)) +
ALIGN_SIZE(sizeof(Query_cache_result)));
#ifndef EMBEDDED_LIBRARY
@@ -2590,36 +2593,20 @@ void Query_cache::invalidate_table(THD *
void Query_cache::invalidate_table(THD *thd, uchar * key, uint32 key_length)
{
- bool interrupt;
- STRUCT_LOCK(&structure_guard_mutex);
- wait_while_table_flush_is_in_progress(&interrupt);
- if (interrupt)
- {
- STRUCT_UNLOCK(&structure_guard_mutex);
+ DBUG_EXECUTE_IF("wait_in_query_cache_invalidate1",
+ debug_wait_for_kill("wait_in_query_cache_invalidate1"); );
+
+ if (try_lock())
return;
- }
- /*
- Setting 'TABLE_FLUSH_IN_PROGRESS' will temporarily disable the cache
- so that structural changes to cache won't block the entire server.
- However, threads requesting to change the query cache will still have
- to wait for the flush to finish.
- */
- m_cache_status= Query_cache::TABLE_FLUSH_IN_PROGRESS;
- STRUCT_UNLOCK(&structure_guard_mutex);
+ DBUG_EXECUTE_IF("wait_in_query_cache_invalidate2",
+ debug_wait_for_kill("wait_in_query_cache_invalidate2"); );
+
if (query_cache_size > 0)
invalidate_table_internal(thd, key, key_length);
- STRUCT_LOCK(&structure_guard_mutex);
- m_cache_status= Query_cache::NO_FLUSH_IN_PROGRESS;
-
- /*
- net_real_write might be waiting on a change on the m_cache_status
- variable.
- */
- pthread_cond_signal(&COND_cache_status_changed);
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
}
@@ -2628,7 +2615,7 @@ void Query_cache::invalidate_table(THD *
The caller must ensure that no other thread is trying to work with
the query cache when this function is executed.
- @pre structure_guard_mutex is acquired or TABLE_FLUSH_IN_PROGRESS is set.
+ @pre structure_guard_mutex is acquired or LOCKED is set.
*/
void
@@ -2646,7 +2633,7 @@ Query_cache::invalidate_table_internal(T
/**
Invalidate a linked list of query cache blocks.
- Each block tries to aquire a block level lock before
+ Each block tries to acquire a block level lock before
free_query is a called. This function will in turn affect
related table- and result-blocks.
@@ -4170,10 +4157,7 @@ my_bool Query_cache::check_integrity(boo
DBUG_ENTER("check_integrity");
if (!locked)
- STRUCT_LOCK(&structure_guard_mutex);
-
- while (is_flushing())
- pthread_cond_wait(&COND_cache_status_changed,&structure_guard_mutex);
+ lock_and_suspend();
if (hash_check(&queries))
{
@@ -4422,7 +4406,7 @@ my_bool Query_cache::check_integrity(boo
}
DBUG_ASSERT(result == 0);
if (!locked)
- STRUCT_UNLOCK(&structure_guard_mutex);
+ unlock();
DBUG_RETURN(result);
}
=== modified file 'sql/sql_cache.h'
--- a/sql/sql_cache.h 2008-07-24 13:41:55 +0000
+++ b/sql/sql_cache.h 2009-06-15 14:55:52 +0000
@@ -272,12 +272,12 @@ public:
private:
+#ifndef DBUG_OFF
+ my_thread_id m_cache_lock_thread_id;
+#endif
pthread_cond_t COND_cache_status_changed;
-
- enum Cache_status { NO_FLUSH_IN_PROGRESS, FLUSH_IN_PROGRESS,
- TABLE_FLUSH_IN_PROGRESS };
-
- Cache_status m_cache_status;
+ enum Cache_lock_status { UNLOCKED, LOCKED_NO_WAIT, LOCKED };
+ Cache_lock_status m_cache_lock_status;
void free_query_internal(Query_cache_block *point);
void invalidate_table_internal(THD *thd, uchar *key, uint32 key_length);
@@ -380,8 +380,6 @@ protected:
Query_cache_block *pprev);
my_bool join_results(ulong join_limit);
- void wait_while_table_flush_is_in_progress(bool *interrupt);
-
/*
Following function control structure_guard_mutex
by themself or don't need structure_guard_mutex
@@ -469,11 +467,6 @@ protected:
friend void query_cache_end_of_result(THD *thd);
friend void query_cache_abort(NET *net);
- bool is_flushing(void)
- {
- return (m_cache_status != Query_cache::NO_FLUSH_IN_PROGRESS);
- }
-
/*
The following functions are only used when debugging
We don't protect these with ifndef DBUG_OFF to not have to recompile
@@ -491,6 +484,10 @@ protected:
Query_cache_block_table * point,
const char *name);
my_bool in_blocks(Query_cache_block * point);
+
+ bool try_lock(void);
+ void lock_and_suspend(void);
+ void unlock(void);
};
extern Query_cache query_cache;
Attachment: [text/bzr-bundle]
