mysql always using maximum connection - mysql

Question

I have LAMP server having 4 core CPU and 32 GB RAM.We are running a large website on it. I have following issues now in my server.
When I use Mysqlreport tool to monitor the mysql server i am always seeing the connection usage as below. And the users reporting connection issues in the website.
_
Connections _______________________________
Max used 251 of 250 %Max: 100.40 Total 748.71k 3.5/s
But when I use "show process list" command it will output nothing. We are using MyISAM engine for all our DBs.
My Mysql Config File is pasted below:
######################
[mysqld]
max_connections = 250
set-variable=local-infile=0
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
skip-name-resolve
skip-bdb
wait_timeout = 60
thread_cache_size = 100
table_cache = 1024
key_buffer = 384M
log_slow_queries=/mysql-log/mysql-slow.log
query-cache-size=512M
query-cache-type=1
query_cache_limit=20M
[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
#
Who is using my Mysql connection pool? How can I find it?
And i have another issue.
Sometimes the Load average goes beyond 4-8 range. See below:
13:40:02 up 2 days, 10:39, 0 users, load average: 5.03, 1.68, 0.93
At that time i can see mysql is the top consumer of the CPU. Is there any optimization needed in mysql Server?
Please reply to my above two queries.
Thanks in advance,
Aruns

Answer 1

I noticed that you are already using MySQL Query Cache.
Have you tried using MySQL workbench to connect to your MySQL database? It offers a graphical way of checking out your MySQL database, including process list.
If you are behind a firewall, try using
show full processlist
However, I think this will not really help.
I would assume that you are using PHP - MySQL to serve out web pages. So this means that you will mostly find that the MySQL connections are made from PHP. To see how many apache threads are running at one time. You can try:
ps aux |grep httpd |wc -l
If you have many more threads on apache, connecting to MySQL, then you know you have a problem.
You mentioned that you have a busy site, therefore, therefore the real answer to your problem is to cache your content, probably using memcached. The idea is to reduce the hits to your MySQL server. Your server has plenty of RAM and perfect for memcached.
This idea is reuse the content for a certain amount of time depending if the content needs freshness:
<?php
$cachedContent = $memcache->get("cacheKey");
if (!$cachedContent) {
// retrieve from MySQL and formulate HTML here
// you can use obstart so that you can reuse your previous code
ob_start();
// your previous code here
// echo or
?>
<div>
previous generated content from mysql
</div>
<?php
// now cachedContent contains your previous generated HTML
$cachedContent = ob_get_contents();
// set content into memcache
$memcache->set("cacheKey", $cachedContent, false, 1800);
// clear the buffer
ob_end_flush();
}
echo $cachedContent;
?>
You need to find which contents to cache first. Good places to start are:
Inefficient bits on the index.php page (I assume this will be one of the most hit page)
Check your GA for most hit pages.
Check your MySQL slow queries and cache those contents.

Answer 2

Add the below variables in your my.cnf :
If you are going to use only MyISAM engine below variables will give the best result according to your Hardware configuration .
max_allowed_packet = 1M
table_open_cache = 250
sort_buffer_size = 2M
thread_stack = 128K
join_buffer_size = 1M
query_cache_limit = 400k
query_cache_size = 300M
key_buffer_size = 5G
read_buffer_size = 2M
read_rnd_buffer_size = 2M
bulk_insert_buffer_size = 8M
myisam_sort_buffer_size = 8M
myisam_max_sort_file_size = 6G
myisam_recover=FORCE,BACKUP
But depends on your DB size and how your application is accessing(fetching) the data, we can modify the above variables.
Reduce the wait_timeout=30.
Regarding this really i dont have any clue :( ..
Connections _________________
Max used 251 of 250 %Max: 100.40 Total 748.71k 3.5/s
SHOW PROCESSLIST\g
SHOULD PROVIDE THE LIST OF PROCESS ARE CONNECTED TO DB IN ANY STATE (SLEEP/READING..... ETC.,)
Add the above variables in your my.cnf and restart the server .