as swapping increases the latency of each request beyond a point
that users consider "fast enough". This causes users to hit
stop and reload, further increasing the load. You can, and
- should, control the <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> setting, so that your server
+ should, control the <code class="directive"><a href="../mod/mpm_common.html#maxrequestworkers">MaxRequestWorkers</a></code> setting so that your server
does not spawn so many children that it starts swapping. The procedure
for doing this is simple: determine the size of your average Apache
process, by looking at your process list via a tool such as
</Directory></pre>
- <p>and a request is made for the URI <code>/index.html</code>.
- Then Apache will perform <code>lstat(2)</code> on
+ <p>and a request is made for the URI <code>/index.html</code>,
+ then Apache will perform <code>lstat(2)</code> on
<code>/www</code>, <code>/www/htdocs</code>, and
<code>/www/htdocs/index.html</code>. The results of these
<code>lstats</code> are never cached, so they will occur on
<p>This at least avoids the extra checks for the
<code class="directive"><a href="../mod/core.html#documentroot">DocumentRoot</a></code> path.
- Note that you'll need to add similar sections, if you
+ Note that you'll need to add similar sections if you
have any <code class="directive"><a href="../mod/mod_alias.html#alias">Alias</a></code> or
<code class="directive"><a href="../mod/mod_rewrite.html#rewriterule">RewriteRule</a></code> paths
outside of your document root. For highest performance,
- <p>If at all possible, avoid content negotiation, if you're
+ <p>If at all possible, avoid content negotiation if you're
really interested in every last ounce of performance. In
practice the benefits of negotiation outweigh the performance
penalties. There's one case where you can speed up the server.
<p>In situations where Apache 2.x needs to look at the contents
of a file being delivered--for example, when doing server-side-include
- processing--it normally memory-maps the file, if the OS supports
+ processing--it normally memory-maps the file if the OS supports
some form of <code>mmap(2)</code>.</p>
<p>On some platforms, this memory-mapping improves performance.
<p>In situations where Apache 2.x can ignore the contents of the file
to be delivered -- for example, when serving static file content --
- it normally uses the kernel sendfile support for the file, if the OS
+ it normally uses the kernel sendfile support for the file if the OS
supports the <code>sendfile(2)</code> operation.</p>
<p>On most platforms, using sendfile improves performance by eliminating
setting. So a server being accessed by 100 simultaneous
clients, using the default <code class="directive"><a href="../mod/mpm_common.html#startservers">StartServers</a></code> 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,
+ 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>
performance, you should attempt to eliminate modules that you are
not actually using. If you have built the modules as <a href="../dso.html">DSOs</a>, eliminating modules is a simple
matter of commenting out the associated <code class="directive"><a href="../mod/mod_so.html#loadmodule">LoadModule</a></code> directive for that module.
- This allows you to experiment with removing modules, and seeing
+ This allows you to experiment with removing modules and seeing
if your site still functions in their absence.</p>
<p>If, on the other hand, you have modules statically linked
accomplishing nothing. Meanwhile none of those children are
servicing requests that occurred on other sockets until they
get back up to the <code>select</code> again. Overall this
- solution does not seem very fruitful, unless you have as many
+ solution does not seem very fruitful unless you have as many
idle CPUs (in a multiprocessor box) as you have idle children
(not a very likely situation).</p>
<p>The above is fine and dandy for multiple socket servers, but
what about single socket servers? In theory they shouldn't
- experience any of these same problems, because all children can
- just block in <code>accept(2)</code> until a connection
+ experience any of these same problems because all the children
+ can just block in <code>accept(2)</code> until a connection
arrives, and no starvation results. In practice this hides
almost the same "spinning" behavior discussed above in the
non-blocking solution. The way that most TCP stacks are
implemented, the kernel actually wakes up all processes blocked
in <code>accept</code> when a single connection arrives. One of
- those processes gets the connection and returns to user-space,
- the rest spin in the kernel and go back to sleep when they
+ those processes gets the connection and returns to user-space.
+ The rest spin in the kernel and go back to sleep when they
discover there's no connection for them. This spinning is
hidden from the user-land code, but it's there nonetheless.
This can result in the same load-spiking wasteful behavior
an HTTP server to <strong>reliably</strong> implement the
protocol, it needs to shut down each direction of the
communication independently. (Recall that a TCP connection is
- bi-directional, each half is independent of the other.)</p>
+ bi-directional. Each half is independent of the other.)</p>
<p>When this feature was added to Apache, it caused a flurry of
problems on various versions of Unix because of shortsightedness.
<div class="note">Note the lack of <code>accept(2)</code> serialization. On this
particular platform, the worker MPM uses an unserialized accept by
- default, unless it is listening on multiple ports.</div>
+ default unless it is listening on multiple ports.</div>
<div class="example"><pre>/65: lwp_park(0x00000000, 0) = 0
/67: lwp_unpark(65, 1) = 0</pre></div>
projects / apache / commitdiff