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<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE refentry PUBLIC "-//Samba-Team//DTD DocBook V4.2-Based Variant V1.0//EN" "http://www.samba.org/samba/DTD/samba-doc">
<refentry id="vfs_preopen.8">
<refmeta>
<refentrytitle>vfs_preopen</refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo class="source">Samba</refmiscinfo>
<refmiscinfo class="manual">System Administration tools</refmiscinfo>
<refmiscinfo class="version">4.1</refmiscinfo>
</refmeta>
<refnamediv>
<refname>vfs_preopen</refname>
<refpurpose>Hide read latencies for applications reading numbered files</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>vfs objects = preopen</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>DESCRIPTION</title>
<para>This VFS module is part of the
<citerefentry><refentrytitle>samba</refentrytitle>
<manvolnum>7</manvolnum></citerefentry> suite.</para>
<para>This module assists applications that want to read numbered
files in sequence with very strict latency requirements. One area
where this happens in video streaming applications that want to read
one file per frame.</para>
<para>When you use this module, a number of helper processes is
started that speculatively open files and read a number of bytes to
prime the file system cache, so that later on when the real
application's request comes along, no disk access is necessary.</para>
<para>This module is stackable.</para>
</refsect1>
<refsect1>
<title>OPTIONS</title>
<variablelist>
<varlistentry>
<term>preopen:names = /pattern/</term>
<listitem>
<para>
preopen:names specifies the file name pattern which should
trigger the preopen helpers to do their work. We assume that
the files are numbered incrementally. So if your file names
are numbered FRAME00000.frm FRAME00001.frm and so on you would
list them as <command>preopen:names=/FRAME*.frm/</command>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>preopen:num_bytes = BYTES</term>
<listitem>
<para>
Specifies the number of bytes the helpers should speculatively
read, defaults to 1.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>preopen:helpers = NUM-PROCS</term>
<listitem>
<para>
Number of forked helper processes, defaults to 1.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>preopen:queuelen = NUM-FILES</term>
<listitem>
<para>
Number of files that should be speculatively opened. Defaults
to the 10 subsequent files.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>VERSION</title>
<para>This man page is correct for version 3.3 of the Samba suite.
</para>
</refsect1>
<refsect1>
<title>AUTHOR</title>
<para>The original Samba software and related utilities
were created by Andrew Tridgell. Samba is now developed
by the Samba Team as an Open Source project similar
to the way the Linux kernel is developed.</para>
<para>The PREOPEN VFS module was created with contributions from
Volker Lendecke and the developers at IBM.
</para>
</refsect1>
</refentry>
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