Tuning the Apache MaxClients parameter

One thing that can have a really drastic effect on a large site using Apache, is the value assigned to the MaxClients parameter.

This parameter defines how many simultaneous request can be served. Any connection request from browsers that come in after that will be queued.

Apache prefork, StartServers, MaxSpareServers and MinSpareServers

In the most common case, you will be using Apache in the prefork mode, meaning one process per connection, with a pool of processes pre-forked to standby for connections. The number of spare processes is defined by the values MaxSpareServers, MinSpareServers, while the number to start is defined by StartServers.

Maxclients default

By default, the MaxClients parameter has a compiled in hard limit of 256. This can be changed by recompiling Apache however. Some distributions, or hosting companies raise this limit to a very high value, such as 512 or even 1024 in order to cope with large loads.

While this makes sense when the web server is serving static content (plain HTML, images, …etc.), it can be detrimental to a dynamic web application like Drupal. So often, we have clients calling because their web server has grind to a halt, and the reason would be a too high MaxClients value. Read more…

Calculate Mysql memory

MySQL memory = key_buffer + max_connections * (join_buffer + record_buffer + sort_buffer + thread_stack + tmp_table_size)

OPTIMISING MYSQL

To obtain the stat of your mysql server since it has been loaded, run mysqladmin processlist extended-status as mentionned above.
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System Tuning Info for Linux Servers

NOTE: Most of the info on this page is about 3 years, and one or two kernel versions out of date.

This page is about optimizing and tuning Linux based systems for server oriented tasks. Most of the info presented here I’ve used myself, and have found it to be beneficial. I’ve tried to avoid the well tread ground (hdparm, turning off hostname lookups in apache, etc) as that info is easy to find elsewhere.
Some cases where you might want to apply some of benchmarking, high traffic web sites, or in case of any load spike (say, a web transfered virus is pegging your servers with bogus requests)
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Displaying PHP APC Cache Information

APC is the Alternative PHP Cache, which is a free, open, and robust framework for caching and optimizing PHP intermediate code. I posted about how to install APC on Linux a couple of days ago, and will now look at the apc.php script which comes with APC and shows information about how much of the cache is being used, what files are being cached, the number of times they’ve been accessed etc.
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Installing the Alternative PHP Cache (APC)

APC is the Alternative PHP Cache, which is a free, open, and robust framework for caching and optimizing PHP intermediate code. What this means is that APC reads your PHP files, parses them into a more efficient binary format and then caches them in memory so that each request for your PHP files and PHP library files can be fed from the parsed cache. This will generally lead to a speed increase when serving a PHP site, especially one with a lot of library files. This post looks at how to install APC for PHP on Linux. The Linux distribution I used was CentOS 5, but it should be fairly similar for most distros.
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