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How can I reduce that number? I have a quad core machine. Do I need to edit thread_pool_size and by reducing them do I get better performance?

Should a lot of queries or something happen could is choke the machine?

max_connections = 500
max_user_connections = 25
key_buffer = 64M
myisam_sort_buffer_size = 32M
join_buffer_size = 2M
read_buffer_size = 2M
sort_buffer_size = 2M
read_rnd_buffer_size = 2M
table_cache = 1024
thread_cache_size = 16K
wait_timeout = 20
connect_timeout = 10
tmp_table_size = 128M
max_heap_table_size = 128M
max_allowed_packet = 160M
max_connect_errors = 10
query_cache_limit = 1M
query_cache_size = 16M
query_cache_type = 1

open_files_limit = 8192

max_allowed_packet = 16M

key_buffer = 64M
sort_buffer = 64M
read_buffer = 16M
write_buffer = 16M
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Could you show relevant entries from your my.cnf please? Also, those threads seem to be bored. Have a look at SHOW PROCESSLIST FULL. – Alexander Janssen Nov 2 '12 at 20:07
added to the top – Julia Roberts Nov 2 '12 at 20:13
Do you actually observe any performance problems? It's usually no problem having a few dozen idling threads. Is there anything really happening? Check with SHOW PROCESSLIST FULL – Alexander Janssen Nov 2 '12 at 20:16
up vote 0 down vote accepted

Seems like you have broken indexes, or even likely - "slow" queries with no indexes.

Keep in mind that there is VERY dangerous to increase max_connections blindly. Each thread bite alot of memory for buffering, and, probably, you run out of RAM and get heavy paging and slowdown instead acceleration.

Turn on slow queries logging:

SET @@global.log_slow_queries = 1;
SET @@global.log_queries_not_using_indexes = 1;

and check for rows with high value in Rows_examined:

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