<summary>
- <p>Apache 2.x is a general-purpose webserver, designed to
+ <note type="warning"><title>Warning</title>
+ <p>This document is partially out of date and might be inaccurate.</p>
+ </note>
+
+ <p>Apache 2.4 is a general-purpose webserver, designed to
provide a balance of flexibility, portability, and performance.
Although it has not been designed specifically to set benchmark
- records, Apache 2.x is capable of high performance in many
+ records, Apache 2.4 is capable of high performance in many
real-world situations.</p>
- <p>Compared to Apache 1.3, release 2.x contains many additional
- optimizations to increase throughput and scalability. Most of
- these improvements are enabled by default. However, there are
- compile-time and run-time configuration choices that can
- significantly affect performance. This document describes the
- options that a server administrator can configure to tune the
- performance of an Apache 2.x installation. Some of these
- configuration options enable the httpd to better take advantage
- of the capabilities of the hardware and OS, while others allow
+ <p>This document describes the options that a server administrator
+ can configure to tune the performance of an Apache 2.4 installation.
+ Some of these configuration options enable the httpd to better take
+ advantage of the capabilities of the hardware and OS, while others allow
the administrator to trade functionality for speed.</p>
</summary>
needed to enable it. (With Linux, for example, this means
using Linux 2.4 or later. For early releases of Solaris 8,
you may need to apply a patch.) On systems where it is
- available, <code>sendfile</code> enables Apache 2 to deliver
+ available, <code>sendfile</code> enables Apache to deliver
static content faster and with lower CPU utilization.</p>
</li>
</ul>
<p>Prior to Apache 1.3, <directive module="core"
>HostnameLookups</directive> defaulted to <code>On</code>.
- This adds latency to every request because it requires a
- DNS lookup to complete before the request is finished. In
- Apache 1.3 this setting defaults to <code>Off</code>. If you need
- to have addresses in your log files resolved to hostnames, use the
- <program>logresolve</program>
- program that comes with Apache, or one of the numerous log
- reporting packages which are available.</p>
-
- <p>It is recommended that you do this sort of postprocessing of
+ causing an extra latency penalty for every request due to a
+ DNS lookup to complete before the request was finished.
+ In Apache 2.4 this setting defaults to <code>Off</code>. If you need
+ to have addresses in your log files resolved to hostnames, please
+ consider post-processing rather than forcing Apache to do it in the first
+ place. It is recommended that you do this sort of post-processing of
your log files on some machine other than the production web
server machine, in order that this activity not adversely affect
server performance.</p>
an IP address) then you will pay for
two DNS lookups (a reverse, followed by a forward lookup
to make sure that the reverse is not being spoofed). For best
- performance, therefore, use IP addresses, rather than names, when
- using these directives, if possible.</p>
+ performance, whenever it is possible, use IP addresses rather
+ than domain names.</p>
+
+ <note type="warning"><title>Warning:</title>
+ <p>Please use the <directive
+ module="mod_authz_core">Require</directive> directive with Apache 2.4;
+ more info in the related <a href="../upgrading.html">upgrading guide</a>.</p>
+ </note>
<p>Note that it's possible to scope the directives, such as
within a <code><Location "/server-status"></code> section.
except for <code>.html</code> and <code>.cgi</code> files:</p>
<highlight language="config">
-HostnameLookups off
<Files ~ "\.(html|cgi)$">
HostnameLookups on
</Files>
<section id="process">
- <title>Process Creation</title>
-
- <p>Prior to Apache 1.3 the <directive module="prefork"
- >MinSpareServers</directive>, <directive module="prefork"
- >MaxSpareServers</directive>, and <directive module="mpm_common"
- >StartServers</directive> settings all had drastic effects on
- benchmark results. In particular, Apache required a "ramp-up"
- period in order to reach a number of children sufficient to serve
- the load being applied. After the initial spawning of
- <directive module="mpm_common">StartServers</directive> children,
- only one child per second would be created to satisfy the
- <directive module="prefork">MinSpareServers</directive>
- setting. So a server being accessed by 100 simultaneous
- clients, using the default <directive module="mpm_common"
- >StartServers</directive> of <code>5</code> would take on
- the order of 95 seconds to spawn enough children to handle
- the load. This works fine in practice on real-life servers
- because they aren't restarted frequently. But it does really
- poorly on benchmarks which might only run for ten minutes.</p>
-
- <p>The one-per-second rule was implemented in an effort to
- avoid swamping the machine with the startup of new children. If
- the machine is busy spawning children, it can't service
- requests. But it has such a drastic effect on the perceived
- performance of Apache that it had to be replaced. As of Apache
- 1.3, the code will relax the one-per-second rule. It will spawn
- one, wait a second, then spawn two, wait a second, then spawn
- four, and it will continue exponentially until it is spawning
- 32 children per second. It will stop whenever it satisfies the
- <directive module="prefork">MinSpareServers</directive>
- setting.</p>
-
- <p>This appears to be responsive enough that it's almost
- unnecessary to twiddle the <directive module="prefork"
- >MinSpareServers</directive>, <directive module="prefork"
- >MaxSpareServers</directive> and <directive module="mpm_common"
- >StartServers</directive> knobs. When more than 4 children are
- spawned per second, a message will be emitted to the
- <directive module="core">ErrorLog</directive>. If you
- see a lot of these errors, then consider tuning these settings.
- Use the <module>mod_status</module> output as a guide.</p>
-
- <p>Related to process creation is process death induced by the
- <directive module="mpm_common">MaxConnectionsPerChild</directive>
- setting. By default this is <code>0</code>,
- which means that there is no limit to the number of connections
- handled per child. If your configuration currently has this set
- to some very low number, such as <code>30</code>, you may want to bump this
- up significantly. If you are running SunOS or an old version of
- Solaris, limit this to <code>10000</code> or so because of memory leaks.</p>
-
- <p>When keep-alives are in use, children will be kept busy
- doing nothing waiting for more requests on the already open
+ <title>Recycle child processes</title>
+
+ <p><directive module="mpm_common">MaxConnectionsPerChild</directive>
+ limits the numbers of connections that a child process can handle during
+ its lifetime (by default set to <code>0</code> - unlimited). This affects all
+ the <a href="../mpm.html#defaults">MPMs</a>, even the ones using threads.
+ For example, each process created by the <module>worker</module> MPM spawns
+ multiple threads that will handle connections, but this does not influence
+ the overall count. It only means that the sum of requests handled by all the
+ threads spawned by a single process will be counted against the
+ <directive module="mpm_common">MaxConnectionsPerChild</directive> value.</p>
+
+ <p><directive module="mpm_common">MaxConnectionsPerChild</directive> should
+ not have any limit in the optimal use case, since there should not be any
+ reason to force a process kill other than software bugs causing memory leaks
+ or excessive CPU usage.</p>
+
+ <p>When keep-alives are in use, a process (or a thread spawned by a process)
+ will be kept busy doing nothing but waiting for more requests on the already open
connection. The default <directive module="core"
>KeepAliveTimeout</directive> of <code>5</code>
seconds attempts to minimize this effect. The tradeoff here is
- between network bandwidth and server resources. In no event
- should you raise this above about <code>60</code> seconds, as <a
- href="http://www.hpl.hp.com/techreports/Compaq-DEC/WRL-95-4.html">
- most of the benefits are lost</a>.</p>
-
+ between network bandwidth and server resources.</p>
</section>
</section>
projects / thirdparty / apache / httpd.git / commitdiff
