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Re: Problems with system locking
Posted by: Ananth Reddy
Date: July 14, 2006 03:52PM

Here is an update on this problem:

we were able to recreate in our testing environment by creating load on server
We killed the process to dump trace (see below) and looked at the source code to see what thread doing while pegging CPU and freezing system

As it turnsout thet it is a "kind of garbage collection problem" for query_cache
Thread was spending all time managing free list in query cache

we had 500MB of query cache and it was not effective in our environment as our tables were very dynamic with lots of updates.

The workaround was to remove complete query cache by

set global query_cache_size = 0;

And problem went away

This looks like mysql BUG to me and I haven't opened BUG yet but I'll.

Thanks for all the help I got from these forums in debugging this prblem

Here is the stack trace:

0x808d903 handle_segfault + 423
0x82e8d98 pthread_sighandler + 184
0x81234db insert_into_free_memory_sorted_list__11Query_cacheP17Query_cache_blockPP17Query_cache_block + 95
0x81233b1 insert_into_free_memory_list__11Query_cacheP17Query_cache_block + 53
0x81231fd free_memory_block__11Query_cacheP17Query_cache_block + 93
0x812279f free_query__11Query_cacheP17Query_cache_block + 219
0x81226a4 free_old_query__11Query_cache + 84
0x8123025 allocate_block__11Query_cacheUlcUlc + 137
0x81227f1 write_block_data__11Query_cacheUlPcUlQ217Query_cache_block10block_typeUic + 69
0x8121632 store_query__11Query_cacheP3THDP13st_table_list + 454
0x809da46 mysql_execute_command__FP3THD + 1258
0x80a223f mysql_parse__FP3THDPcUi + 211
0x809c6ef dispatch_command__F19enum_server_commandP3THDPcUi + 1547
0x809c0d8 do_command__FP3THD + 188
0x809b7a7 handle_one_connection + 615
0x82e654c pthread_start_thread + 220
0x830fe0a thread_start + 4

ananth



Edited 1 time(s). Last edit at 07/14/2006 03:54PM by Ananth Reddy.

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