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author | kroki/tomash@moonlight.intranet <> | 2006-08-22 11:47:52 +0400 |
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committer | kroki/tomash@moonlight.intranet <> | 2006-08-22 11:47:52 +0400 |
commit | 0f0ddc398a5b68f3a67794c82e7a40cb44a6e402 (patch) | |
tree | 6da805e8e859d377d16c5f512dfe034ba5c7ecb2 /sql/sql_cache.h | |
parent | bf10578fde502a81f56eaf91d556930ae0327893 (diff) | |
download | mariadb-git-0f0ddc398a5b68f3a67794c82e7a40cb44a6e402.tar.gz |
BUG#21051: RESET QUERY CACHE very slow when query_cache_type=0
There were two problems: RESET QUERY CACHE took a long time to complete
and other threads were blocked during this time.
The patch does three things:
1 fixes a bug with improper use of test-lock-test_again technique.
AKA Double-Checked Locking is applicable here only in few places.
2 Somewhat improves performance of RESET QUERY CACHE.
Do my_hash_reset() instead of deleting elements one by one. Note
however that the slowdown also happens when inserting into sorted
list of free blocks, should be rewritten using balanced tree.
3 Makes RESET QUERY CACHE non-blocking.
The patch adjusts the locking protocol of the query cache in the
following way: it introduces a flag flush_in_progress, which is
set when Query_cache::flush_cache() is in progress. This call
sets the flag on enter, and then releases the lock. Every other
call is able to acquire the lock, but does nothing if
flush_in_progress is set (as if the query cache is disabled).
The only exception is the concurrent calls to
Query_cache::flush_cache(), that are blocked until the flush is
over. When leaving Query_cache::flush_cache(), the lock is
acquired and the flag is reset, and one thread waiting on
Query_cache::flush_cache() (if any) is notified that it may
proceed.
Diffstat (limited to 'sql/sql_cache.h')
-rw-r--r-- | sql/sql_cache.h | 17 |
1 files changed, 16 insertions, 1 deletions
diff --git a/sql/sql_cache.h b/sql/sql_cache.h index 29d314d3c44..a66067159e2 100644 --- a/sql/sql_cache.h +++ b/sql/sql_cache.h @@ -195,7 +195,6 @@ extern "C" byte *query_cache_table_get_key(const byte *record, uint *length, my_bool not_used); } -void query_cache_insert(NET *thd, const char *packet, ulong length); extern "C" void query_cache_invalidate_by_MyISAM_filename(const char* filename); @@ -241,6 +240,12 @@ public: ulong free_memory, queries_in_cache, hits, inserts, refused, free_memory_blocks, total_blocks, lowmem_prunes; +private: + pthread_cond_t COND_flush_finished; + bool flush_in_progress; + + void free_query_internal(Query_cache_block *point); + protected: /* The following mutex is locked when searching or changing global @@ -249,6 +254,12 @@ protected: LOCK SEQUENCE (to prevent deadlocks): 1. structure_guard_mutex 2. query block (for operation inside query (query block/results)) + + Thread doing cache flush releases the mutex once it sets + flush_in_progress flag, so other threads may bypass the cache as + if it is disabled, not waiting for reset to finish. The exception + is other threads that were going to do cache flush---they'll wait + till the end of a flush operation. */ pthread_mutex_t structure_guard_mutex; byte *cache; // cache memory @@ -358,6 +369,7 @@ protected: If query is cacheable return number tables in query (query without tables not cached) */ + static TABLE_COUNTER_TYPE is_cacheable(THD *thd, uint32 query_len, char *query, LEX *lex, TABLE_LIST *tables_used, uint8 *tables_type); @@ -410,6 +422,7 @@ protected: void destroy(); + friend void query_cache_init_query(NET *net); friend void query_cache_insert(NET *net, const char *packet, ulong length); friend void query_cache_end_of_result(THD *thd); friend void query_cache_abort(NET *net); @@ -435,6 +448,8 @@ protected: extern Query_cache query_cache; extern TYPELIB query_cache_type_typelib; +void query_cache_init_query(NET *net); +void query_cache_insert(NET *net, const char *packet, ulong length); void query_cache_end_of_result(THD *thd); void query_cache_abort(NET *net); |