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Code Editor : mod_statcache.html

<!DOCTYPE html>
<html>
<head>
<title>ProFTPD module mod_statcache</title>
</head>

<hr>
<center>
<h2>ProFTPD module <code>mod_statcache</code></h2>
</center>
<hr>

The <code>mod_statcache</code> module is designed to cache the results
of <code>stat(2)</code> and <code>lstat(2)</code> calls in shared memory,
so that the results can be shared among multiple session processes. On
a busy server, especially one handling many directory listings, these
<code>stat(2)</code>/<code>lstat(2)</code> calls can add quite a bit of
overhead.

This module is contained in the <code>mod_statcache.c</code> file for
ProFTPD 1.3.x, and is not compiled by default. Installation
instructions are discussed <a href="#Installation">here</a>. More examples
of <code>mod_statcache</code> usage can be found <a href="#Usage">here</a>.

The most current version of <code>mod_statcache</code> is distributed with the
ProFTPD source code.

<h2>Author</h2>

Please contact TJ Saunders &lt;tj at castaglia.org&gt; with any
questions, concerns, or suggestions regarding this module.

<h2>Directives</h2>
<ul>
 <li><a href="#StatCacheCapacity">StatCacheCapacity</a>
 <li><a href="#StatCacheControlsACLs">StatCacheControlsACLs</a>
 <li><a href="#StatCacheEngine">StatCacheEngine</a>
 <li><a href="#StatCacheMaxAge">StatCacheMaxAge</a>
 <li><a href="#StatCacheTable">StatCacheTable</a>
</ul>

<h2>Control Actions</h2>
<ul>
 <li><a href="#statcache"><code>statcache</code></a>
</ul>

<hr>
<h3><a name="StatCacheCapacity">StatCacheCapacity</a></h3>
Syntax: StatCacheCapacity count 
Default: StatCacheCapacity 5000 
Context: server config 
Module: mod_statcache 
Compatibility: 1.3.4rc2 and later

The <code>StatCacheCapacity</code> directive configures the capacity
of the cache, i.e. the maximum number of cache entries. By default,
<code>mod_statcache</code> allocates space for 5000 cache entries.

The count value be 10 or greater. The configured count
is handled as a hint; the actual allocated capacity may be rounded up
to the nearest multiple of the internal block sizes.

<hr>
<h3><a name="StatCacheControlsACLs">StatCacheControlsACLs</a></h3>
Syntax: StatCacheControlsACLs actions|&quot;all&quot; &quot;allow&quot;|&quot;deny&quot; &quot;user&quot;|&quot;group&quot; list 
Default: None 
Context: server config 
Module: mod_statcache 
Compatibility: 1.3.4rc2 and later

The <code>StatCacheControlsACLs</code> directive configures access lists of
users or groups who are allowed (or denied) the ability to
use the actions implemented by <code>mod_statcache</code>. The default
behavior is to deny everyone unless an ACL allowing access has been explicitly
configured.

If &quot;allow&quot; is used, then list, a comma-delimited list
of users or groups, can use the given actions; all
others are denied. If &quot;deny&quot; is used, then the list of
users or groups cannot use actions all others are
allowed. Multiple <code>StatCacheControlsACLs</code> directives may be used to
configure ACLs for different control actions, and for both users and groups.

The action provided by <code>mod_statcache</code> is
<a href="#statcache">&quot;statcache&quot;</a>.

Examples:
<pre>
 # Allow only user root to examine cache stats
 StatCacheControlsACLs all allow user root
</pre>

<hr>
<h3><a name="StatCacheEngine">StatCacheEngine</a></h3>
Syntax: StatCacheEngine on|off 
Default: StatCacheEngine off 
Context: server config, <code>&lt;VirtualHost&gt;</code>, <code>&lt;Global&gt;</code> 
Module: mod_statcache 
Compatibility: 1.3.4rc2 and later

The <code>StatCacheEngine</code> directive enables or disables the module's
caching of <code>stat(2)</code> and <code>lstat(2)</code> calls.

<hr>
<h3><a name="StatCacheMaxAge">StatCacheMaxAge</a></h3>
Syntax: StatCacheMaxAge positive-cache-age [negative-cache-age] 
Default: StatCacheMaxAge 5 
Context: server config 
Module: mod_statcache 
Compatibility: 1.3.4rc2 and later

The <code>StatCacheMaxAge</code> directive configures how long the
<code>mod_statcache</code> module will keep the <code>stat(2)</code> or
<code>lstat(2)</code> results cached for a given path. By default,
<code>mod_statcache</code> will cache results for 5 seconds (and will
cache failed <code>stat(2)</code>/<code>lstat(2)</code> calls for
1 second).

If you configure a single age parameter, then that value will be used for
both positive and negative cache entries. Thus:
<pre>
 StatCacheMaxAge 300
</pre>
will cache successful and failed
<code>stat(2)</code>/<code>lstat(2)</code> calls for 5 minutes (300 seconds).

To disable caching of failed <code>stat(2)</code>/<code>lstat(2)</code> calls
entirely, use a negative-cache-age value of zero, e.g.:
<pre>
 # Cache lookups for 60 seconds, and do not cache failed lookups
 StatCacheMaxAge 60 0
</pre>

<hr>
<h3><a name="StatCacheTable">StatCacheTable</a></h3>
Syntax: StatCacheTable path 
Default: None 
Context: server config 
Module: mod_statcache 
Compatibility: 1.3.4rc2 and later

The <code>StatCacheTable</code> directive configures a path to a file
that <code>mod_statcache</code> uses for handling its cache data. The given
path must be an absolute path. Note: this directive is
required for <code>mod_statcache</code> to function. It is recommended
that this file not be on an NFS mounted partition.

Note that statcache data is not kept across daemon stop/starts. That is,
once <code>proftpd</code> is shutdown, all current statcache data is lost.

<hr>
<h2>Control Actions</h2>

<hr>
<h3><a name="statcache"><code>statcache</code></a></h3>
Syntax: ftpdctl statcache info|dump 
Purpose: Display statcache information

The <code>statcache</code> action is used to display cache statistics about
the statcache data maintained by <code>mod_statcache</code>. For example:
<pre>
 # ftpdctl statcache info
 ftpdctl: hits 773, misses 67: 92.0% hit rate
 ftpdctl: expires 22, rejects 0
 ftpdctl: current count: 1 (of 5000) (0.0% usage)
 ftpdctl: highest count: 45 (of 5000) (0.9% usage)
</pre>
To dump out the entire cache contents (not recommended on a busy server),
you can use:
<pre>
 # ftpdctl statcache dump
</pre>

<hr>
<h2><a name="Installation">Installation</a></h2>
The <code>mod_statcache</code> module is distributed with ProFTPD. For
including <code>mod_statcache</code> as a staticly linked module, use:
<pre>
 $ ./configure --with-modules=mod_statcache
</pre>
To build <code>mod_statcache</code> as a DSO module:
<pre>
 $ ./configure --enable-dso --with-shared=mod_statcache
</pre>
Then follow the usual steps:
<pre>
 $ make
 $ make install
</pre>

For those with an existing ProFTPD installation, you can use the
<code>prxs</code> tool to add <code>mod_statcache</code>, as a DSO module, to
your existing server:
<pre>
 $ prxs -c -i -d mod_statcache.c
</pre>

Note: Use of the <code>mod_statcache</code> module will
interfere with the <code>mod_vroot</code> and <code>mod_quotatab</code>
modules.

<hr>
<h2><a name="Usage">Usage</a></h2>

The <code>mod_statcache</code> module works by allocating a SysV shared
memory segment. The different <code>proftpd</code> session processes
then attach to that shared memory segment so that they can share statcache
results.

Example configuration:
<pre>
 &lt;IfModule mod_statcache.c&gt;
 StatCacheEngine on
 StatCacheTable /var/run/proftpd/statcache.tab
 &lt;/IfModule&gt;
</pre>

</body>
</html>

${this.title}

Code Editor : mod_statcache.html