I'd like to ask your help on a longstanding issue with php/mysql connections.
Every time I execute a "SHOW PROCESSLIST" command it shows me about 400 idle (Status: Sleep) connections to the database Server emerging from our 5 Webservers.
That never was much of a problem (and I didn't find a quick solution) until recently traffic numbers increased and since then MySQL reports the "to many connections" Problems repeatedly, even so 350+ of those connections are in "sleep" state. Also a server can't get a MySQL connection even if there are sleeping connection to that same server.
All those connections vanish when an apache server is restated.
The PHP Code used to create the Database connections uses the normal "mysql" Module, the "mysqli" Module, PEAR::DB and Zend Framework Db Adapter. (Different projects). NONE of the projects uses persistent connections.
Raising the connection-limit is possible but doesn't seem like a good solution since it's 450 now and there are only 20-100 "real" connections at a time anyways.
My question:
Why are there so many connections in sleep state and how can I prevent that?
-- Update:
The Number of Apache requests running at a time never exceeds 50 concurrent requests, so i guess there is a problem with closing the connection or apache keeps the port open without a phpscript attached or something (?)
my.cnf in case it's helpful:
innodb_buffer_pool_size = 1024M
max_allowed_packet = 5M
net_buffer_length = 8K
read_buffer_size = 2M
read_rnd_buffer_size = 8M
query_cache_size = 512M
myisam_sort_buffer_size = 128M
max_connections = 450
thread_cache = 50
key_buffer_size = 1280M
join_buffer_size = 16M
table_cache = 2048
sort_buffer_size = 64M
tmp_table_size = 512M
max_heap_table_size = 512M
thread_concurrency = 8
log-slow-queries = /daten/mysql-log/slow-log
long_query_time = 1
log_queries_not_using_indexes
innodb_additional_mem_pool_size = 64M
innodb_log_file_size = 64M
innodb_log_buffer_size = 8M
innodb_flush_log_at_trx_commit = 2
innodb_file_per_table
Alright so after trying every solution out there to solve this exact issues on a wordpress blog, I might have done something either really stupid or genius... With no idea why there's an increase in Mysql connections, I used the php script below in my header to kill all sleeping processes..
So every visitor to my site helps in killing the sleeping processes..
<?php
$result = mysql_query("SHOW processlist");
while ($myrow = mysql_fetch_assoc($result)) {
if ($myrow['Command'] == "Sleep") {
mysql_query("KILL {$myrow['Id']}");}
}
?>
Before increasing the max_connections variable, you have to check how many non-interactive connection you have by running show processlist command.
If you have many sleep connection, you have to decrease the value of the "wait_timeout" variable to close non-interactive connection after waiting some times.
SHOW SESSION VARIABLES LIKE 'wait_timeout';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| wait_timeout | 28800 |
+---------------+-------+
the value is in second, it means that non-interactive connection still up to 8 hours.
SET session wait_timeout=600; Query OK, 0 rows affected (0.00 sec)
After 10 minutes if the sleep connection still sleeping the mysql or MariaDB drop that connection.
The above solutions like run a query
SET session wait_timeout=600;
Will only work until mysql is restarted. For a persistant solution, edit mysql.conf and add after [mysqld]:
wait_timeout=300
interactive_timeout = 300
Where 300 is the number of seconds you want.
Increasing number of max-connections will not solve the problem.
We were experiencing the same situation on our servers. This is what happens
User open a page/view, that connect to the database, query the database, still query(queries) were not finished and user leave the page or move to some other page. So the connection that was open, will remains open, and keep increasing number of connections, if there are more users connecting with the db and doing something similar.
You can set interactive_timeout MySQL, bydefault it is 28800 (8hours) to 1 hour
SET interactive_timeout=3600
So I was running 300 PHP processes simulatenously and was getting a rate of between 60 - 90 per second (my process involves 3x queries). I upped it to 400 and this fell to about 40-50 per second. I dropped it to 200 and am back to between 60 and 90!
So my advice to anyone with this problem is experiment with running less than more and see if it improves. There will be less memory and CPU being used so the processes that do run will have greater ability and the speed may improve.
Source: Stackoverflow.com