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Previous: <a rel="previous" accesskey="p" href="Memory-cache.html#Memory-cache">Memory cache</a>,
Up: <a rel="up" accesskey="u" href="Caching.html#Caching">Caching</a>
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<h3 class="section">4.3 The on-disk cache</h3>
<p><a name="index-filesystem-203"></a><a name="index-NFS-204"></a><a name="index-diskCacheRoot-205"></a><a name="index-maxDiskEntries-206"></a><a name="index-diskCacheWriteoutOnClose-207"></a><a name="index-diskCacheFilePermissions-208"></a><a name="index-diskCacheDirectoryPermissions-209"></a><a name="index-maxDiskCacheEntrySize-210"></a>
The on-disk cache consists in a filesystem subtree rooted at
a location defined by the variable <code>diskCacheRoot</code>, by default
<code>"/var/cache/polipo/"</code>. This directory should normally be
writeable, readable and seekable by the user running Polipo. While it
is best to use a local filesystem for the on-disk cache, a NFSv3- or
AFS-mounted filesystem should be safe in most implementations. Do not
use NFSv2, as it will cause cache corruption <a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a>.
<p>If <code>diskCacheRoot</code> is an empty string, no disk cache is used.
<p>The value <code>maxDiskEntries</code> (32 by default) is the absolute
maximum of file descriptors held open for on-disk objects. When this
limit is reached, Polipo will close descriptors on
a least-recently-used basis. This value should be set to be slightly
larger than the number of resources that you expect to be live at
a single time; defining the right notion of liveness is left as an
exercise for the interested reader.
<p>The value <code>diskCacheWriteoutOnClose</code> (32<span class="dmn">kB</span> by default) is
the amount of data that Polipo will write out when closing a disk
file. Writing out data when closing a file can avoid subsequently
reopening it, but causes unnecessary work if the instance is later
superseded.
<p>The integers <code>diskCacheDirectoryPermissions</code> and
<code>diskCacheFilePermissions</code> are the Unix filesystem permissions
with which files and directories are created in the on-disk cache;
they default to ‘<samp><span class="samp">0700</span></samp>’ and ‘<samp><span class="samp">0600</span></samp>’ respectively.
<p>The variable <code>maxDiskCacheEntrySize</code> specifies the maximum size,
in bytes, of an instance that is stored in the on-disk cache. If set
to -1 (the default), all objects are stored in the on-disk cache,
<ul class="menu">
<li><a accesskey="1" href="Asynchronous-writing.html#Asynchronous-writing">Asynchronous writing</a>: Writing out data when idle.
<li><a accesskey="2" href="Purging.html#Purging">Purging</a>: Purging the on-disk cache.
<li><a accesskey="3" href="Disk-format.html#Disk-format">Disk format</a>: Format of the on-disk cache.
<li><a accesskey="4" href="Modifying-the-on_002ddisk-cache.html#Modifying-the-on_002ddisk-cache">Modifying the on-disk cache</a>
</ul>
<div class="footnote">
<hr>
<h4>Fußnoten</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> Polipo assumes
that ‘<samp><span class="samp">open(O_CREAT | O_EXCL)</span></samp>’ works reliably.</p>
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