How to optimize Apache performance

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Squeezing the most performance out of your Apache server can make difference in how your Web site functions and the impression it makes. Even fractions of a second matter, especially on dynamic sites.

 

Configuring the MPM

Apache is modular in that you can add and remove features easily. Multi-Processing Modules (MPMs) provide this modular functionality at the core of Apache — managing the network connections and dispatching the requests. MPMs let you use threads or even move Apache to a different operating system.

Only one MPM can be active at one time, and it must be compiled in statically with --with-mpm=(worker|prefork|event).

The traditional model of one process per request is called prefork. A newer, threaded, model is called worker, which uses multiple processes, each with multiple threads to get better performance with lower overhead. The final, event MPM is an experimental module that keeps separate pools of threads for different tasks. To determine which MPM you’re currently using, execute httpd -l

Choosing the MPM to use depends on many factors. Setting aside the event MPM until it leaves experimental status, it’s a choice between threads or no threads. On the surface, threading sounds better than forking, if all the underlying modules are thread safe, including all the libraries used by PHP. Prefork is the safer choice; you should do careful testing if you choose worker. The performance gains also depend on the libraries that come with your distribution and your hardware.

  • The worker MPM uses multiple child processes with many threads each. Each thread handles one connection at a time. Worker generally is a good choice for high-traffic servers because it has a smaller memory footprint than the prefork MPM.
  • The event MPM is threaded like the Worker MPM, but is designed to allow more requests to be served simultaneously by passing off some processing work to supporting threads, freeing up the main threads to work on new requests.
  • The prefork MPM uses multiple child processes with one thread each. Each process handles one connection at a time. On many systems, prefork is comparable in speed to worker, but it uses more memory. Prefork’s threadless design has advantages over worker in some situations: it can be used with non-thread-safe third-party modules, and it is easier to debug on platforms with poor thread debugging support.

Regardless of which MPM you choose, you must configure it appropriately. In general, configuring an MPM involves telling Apache how to control how many workers are running, whether they’re threads or processes. The important configuration options for the prefork MPM are shown below.

 

Optimize apache.conf

To start, open the Apache configuration file and locate the directives section:

On a DirectAdmin based server it will be located in: /etc/httpd/conf/extra/httpd-mpm.conf
On a cPanel server, it will be located in /usr/local/apache/conf/
On a Plesk server, it will be in /etc/httpd/conf/

If you are using nano, vi or vim: once you open the file, you can find the directives by scrolling through the file. Using VI or VIM you can also search by typing forward-slash ‘/’ and typing the exact string that you are looking for (search is case specific).

Timeout


The Timeout setting is the number of seconds before data “sends” or “receives” (to or from the client) time out. Having this set to a high number forces site visitors to “wait in line” which adds extra load to the server. Lowering the ‘Timeout’ value too much will cause a long running script to terminate earlier than expected. A reasonable value is 100 for Virtual Private Servers, or heavily loaded dedicated servers. For Dedicated Servers under normal load the default value of 300 is sufficient.

 

KeepAlive


KeepAlive enables persistent connections on the web server. This setting should be On unless the server is getting requests from hundreds of IPs at once. High volume and/or load balanced servers should have this setting disabled Off to increase connection throughput.

When using DirectAdmin, this directive can be found in: /etc/httpd/conf/extra/httpd-default.conf

 

MaxKeepAliveRequests


This setting limits the number of requests allowed per persistent connection when KeepAlive is on. If it is set to 0, unlimited requests will be allowed. When using DirectAdmin, this directive can be found in: /etc/httpd/conf/extra/httpd-default.conf

It is recommended to keep this value at 100 for virtualized accounts like VPS accounts. On dedicated servers it is recommended that this value be modified to 150.

 

KeepAliveTimeout


The number of seconds Apache will wait for another request before closing the connection. Setting this to a high value may cause performance problems in heavily loaded servers. The higher the timeout, the more server processes will be kept occupied waiting on connections with idle clients. When using DirectAdmin, this directive can be found in: /etc/httpd/conf/extra/httpd-default.conf

The default value of 10 seconds is a good value for average server performance. This value should be kept low as the socket will be idle for extended periods otherwise.It is recommended that this value be lowered to 5 on servers under heavy load.

 

StartServers


sets the number of child server processes created on startup. As the number of processes is dynamically controlled depending on the load there is usually little reason to adjust this parameter. This value should mirror what is set in MinSpareServers.

 

MinSpareServers


Sets the desired minimum number of idle child server processes. An idle process is one which is not handling a request. If there are fewer spareservers idle then specified by this value, then the parent process creates new children at a maximum rate of 1 per second. Setting this parameter to a large number is almost always a bad idea.

cheapbesthost recommends adjusting the value for this setting to the following:

  • Virtual Private Server 5
  • Dedicated server with 1-2GB RAM 10
  • Dedicated server with 2-4GB RAM 20
  • Dedicated server with 4+ GB RAM 25

 

MaxSpareServers


sets the desired maximum number of idle child server processes. An idle process is one which is not handling a request. If there are more than MaxSpareServers idle, then the parent process will kill off the excess processes.

 

ServerLimit


is only used if you need to set MaxClients higher than 256 (default). Do not set the value of this directive any higher than what you might want to set MaxClients to.

 

MaxClients


sets the limit on the number of simultaneous requests that will be served. Any connection attempts over the MaxClients limit will normally be queued, up to a number based on the ListenBacklog directive. Once a child process is freed at the end of a different request, the connection will then be serviced.

For non-threaded servers (i.e., prefork), MaxClients translates into the maximum number of child processes that will be launched to serve requests. The default value is 256; to increase it, you must also raise ServerLimit. this and ServerLimit should be the same or very close with MaxClients never exceeding ServerLimit. For servers under high load this value should be increased. See below for more information on how to define the maxclients directive.

How to define the MaxClients directive

A simple calculation for MaxClients would be: (Total Memory – Critical Services Memory) / Size Per Apache process

I define Critical Services as services such as mySQL, Plesk, DirectAdmin; any service that is required for proper operation of your server.

I’ve used the following commands via shell to determine values for Total Memory, OS Memory, MySQL Memory, and Apache Process Size

TOTAL MEMORY
[root@vps httpd]# free -m
total       used       free     shared    buffers     cached
Mem:          1002        599        402          0         28        337
-/+ buffers/cache:        233        769
Swap:         2047        124       1922

MYSQL MEMORY
[root@vps httpd]# ps aux | grep ‘mysql’ | awk ‘{print $6}’
408
21440
704

APACHE PROCESS SIZE
[root@vps httpd]# ps aux | grep ‘httpd’ | awk ‘{print $6}’
22468
11552
41492
40868
41120
41696
39488
41704
15552
16076
16084
728

In this case the server has 1002Mb of memory allocated, xx used by the OS itself, 21Mb used by mySQL, and each Apache thread averages about 30Mb. MaxClients = (1002 – 21) / 30 therefore MaxClients = 32.7

 

MaxConnectionsPerChild


MaxConnectionsPerChild sets the limit on the number of connections that an individual child server process will handle. After MaxConnectionsPerChild connections, the child process will die. If MaxConnectionsPerChild is 0, then the process will never expire.

Setting MaxConnectionsPerChild to a non-zero value limits the amount of memory that process can consume by (accidental) memory leakage. See below for more information.

How to define the MaxConnectionsPerChild directive

A good calculation for MaxConnectionsPerChild would be: (total amount of daily requests / total number of daily processes)

Determining these values is a bit more complex as it requires some type of statistics package or thorough knowledge of interpreting Apache access logs.

As this does not adversely effect memory usage, only cpu time to cycle the process if you are unable to determine this information the standard 1000 should be used.

Thus a good configuration for this server would be:

StartServers       2
MinSpareServers    3
MaxSpareServers    3
ServerLimit       30
MaxClients        30
MaxRequestsPerChild  1000

Be sure once you’ve saved the file to perform a configuration test before restarting Apache.

[root@vps httpd]# service httpd configtest
Syntax OK
[root@vps httpd]# service httpd restart
Stopping httpd:                                            [  OK  ]
Starting httpd:                                            [  OK  ]
How to optimize Apache performance
Written by: AFRIDA YANTI
Reting: 4.9


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