diff options
Diffstat (limited to 'sql/sql_cache.cc')
| -rw-r--r-- | sql/sql_cache.cc | 31 |
1 files changed, 30 insertions, 1 deletions
diff --git a/sql/sql_cache.cc b/sql/sql_cache.cc index e1df1ce8d9a..9a29350880e 100644 --- a/sql/sql_cache.cc +++ b/sql/sql_cache.cc @@ -1032,6 +1032,13 @@ Query_cache::send_result_to_client(THD *thd, char *sql, uint query_length) Query_cache_block_table *block_table, *block_table_end; ulong tot_length; Query_cache_query_flags flags; + const uint spin_treshold= 50000; + const double lock_time_treshold= 0.1; /* Time in seconds */ + uint spin_count= 0; + int lock_status= 0; + ulong new_time= 0; + ulong stop_time= 0; + DBUG_ENTER("Query_cache::send_result_to_client"); /* @@ -1078,7 +1085,29 @@ Query_cache::send_result_to_client(THD *thd, char *sql, uint query_length) } } - STRUCT_LOCK(&structure_guard_mutex); + stop_time= my_clock()+(ulong)lock_time_treshold*CLOCKS_PER_SEC; + while ((lock_status= pthread_mutex_trylock(&structure_guard_mutex)) == EBUSY + && spin_count < spin_treshold + && new_time < stop_time) + { + spin_count++; + if (spin_count%5) + new_time= my_clock(); + my_sleep(0); + } + + if (lock_status != 0) + { + /* + Query cache is too busy doing something else. + Fall back on ordinary statement execution. We also mark this + query as unsafe to cache because otherwise this thread will + still be halted when the result set is stored to the cache. + */ + thd->lex->safe_to_cache_query= FALSE; + goto err; + } + if (query_cache_size == 0 || flush_in_progress) { DBUG_PRINT("qcache", ("query cache disabled")); |