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Commit a14399ef authored by dgaudet's avatar dgaudet
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document MMAP_SEGMENT_SIZE

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@79451 13f79535-47bb-0310-9956-ffa450edef68
parent db849638
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......@@ -690,17 +690,24 @@ munmap(0x400ee000, 6144) = 0
On some architectures it's slower to <code>mmap</code> small
files than it is to simply <code>read</code> them. The define
<code>MMAP_THRESHOLD</code> can be set to the minimum size required before
using <code>mmap</code>. By default it's set to 0 (except on SunOS4
where experimentation has shown 8192 to be a better value). Using a
tool such as
<a href="http://reality.sgi.com/lm_engr/lmbench/lmbench.html">lmbench</a>
you can determine the optimal setting for your
environment. It may even be the case that <code>mmap</code> isn't used
on your architecture, if so then defining <code>USE_MMAP_FILES</code>
<code>MMAP_THRESHOLD</code> can be set to the minimum
size required before using <code>mmap</code>. By default
it's set to 0 (except on SunOS4 where experimentation has
shown 8192 to be a better value). Using a tool such as <a
href="http://reality.sgi.com/lm_engr/lmbench/lmbench.html">lmbench</a> you
can determine the optimal setting for your environment.
<p>You may also wish to experiment with <code>MMAP_SEGMENT_SIZE</code>
(default 32768) which determines the maximum number of bytes that
will be written at a time from mmap()d files. Apache only resets the
client's <code>Timeout</code> in between write()s. So setting this
large may lock out low bandwidth clients unless you also increase the
<code>Timeout</code>.
<p>It may even be the case that <code>mmap</code> isn't
used on your architecture, if so then defining <code>USE_MMAP_FILES</code>
might work (if it works then report back to us).
<p>Apache does its best to avoid copying bytes around in memory. The
first write of any request typically is turned into a <code>writev</code>
which combines both the headers and the first hunk of data:
......
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