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From stodd...@locus.apache.org
Subject cvs commit: httpd-docs-2.0/htdocs/manual/mod mod_file_cache.html index.html
Date Sun, 30 Jul 2000 04:12:39 GMT
stoddard    00/07/29 21:12:38

  Modified:    htdocs/manual/mod index.html
  Added:       htdocs/manual/mod mod_file_cache.html
  Log:
  mod_file_cache docco
  
  Revision  Changes    Path
  1.31      +2 -2      httpd-docs-2.0/htdocs/manual/mod/index.html
  
  Index: index.html
  ===================================================================
  RCS file: /home/cvs/httpd-docs-2.0/htdocs/manual/mod/index.html,v
  retrieving revision 1.30
  retrieving revision 1.31
  diff -u -r1.30 -r1.31
  --- index.html	2000/07/12 05:01:27	1.30
  +++ index.html	2000/07/30 04:12:37	1.31
  @@ -74,6 +74,8 @@
   <DD>Demonstrates Apache API
   <DT><A HREF="mod_expires.html">mod_expires</A> Apache 1.2 and up
   <DD>Apply Expires: headers to resources
  +<DT><A HREF="mod_file_cache.html">mod_file_cache</A>
  +<DD>Caching files in memory for faster serving.
   <DT><A HREF="mod_headers.html">mod_headers</A> Apache 1.2 and up
   <DD>Add arbitrary HTTP headers to resources
   <DT><A HREF="mod_imap.html">mod_imap</A>
  @@ -97,8 +99,6 @@
   <DD>Determining document types using file extensions.
   <DT><A HREF="mod_mime_magic.html">mod_mime_magic</A>
   <DD>Determining document types using "magic numbers".
  -<DT><A HREF="mod_mmap_static.html">mod_mmap_static</A>
  -<DD>Mapping files into memory for faster serving.
   <DT><A HREF="mod_negotiation.html">mod_negotiation</A>
   <DD>Content negotiation.
   <DT><A HREF="mod_proxy.html">mod_proxy</A>
  
  
  
  1.1                  httpd-docs-2.0/htdocs/manual/mod/mod_file_cache.html
  
  Index: mod_file_cache.html
  ===================================================================
  <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
  <HTML>
   <HEAD>
    <TITLE>Apache module mod_file_cache</TITLE>
   </HEAD>
  <!-- Background white, links blue (unvisited), navy (visited), red (active) -->
   <BODY
    BGCOLOR="#FFFFFF"
    TEXT="#000000"
    LINK="#0000FF"
    VLINK="#000080"
    ALINK="#FF0000"
   >
  <!--#include virtual="header.html" -->
    <H1 ALIGN="CENTER">Module mod_file_cache</H1>
    <P>
    <STRONG>This module should be used with care.  You can easily create a
    broken site using mod_file_cache, so read this document
    carefully.</STRONG>
    </P>
  
    <P>
    <EM>Caching</EM> frequently requested files that change very
    infrequently is a technique for reducing server load. mod_file_cache
    provides two techniques for caching frequently requested
    <EM>static</EM> files.
    Through configuration directives, you can direct mod_file_cache
    to either open then mmap()a file, or to pre-open a file and save
    the file's open <EM>file handle</EM>. Both techniques reduce server
    load when processing requests for these files by doing part of the
    work (specifically, the file I/O) for serving the file when the server
    is started rather than during each request. 
    </P>
  
    <P>
    <CODE>mod_file_cache</CODE> is not compiled into the server by
    default. To use <CODE>mod_file_cache</CODE> you have to enable the
    following line in the server build <CODE>Configuration</CODE> file:
    <PRE>
      AddModule  modules/experimental/mod_file_cache.o
    </PRE>
    </P>
  
    <P>
    Notice: You cannot use this for speeding up CGI programs or other files
    which are served by special content handlers. It can only be used for
    regular files which are usually served by the Apache core content handler.
    </P>
  
    <P>
    This module is an extension of and borrows heavily from the
    mod_mmap_static module in Apache 1.3.
    </P>
    <H2>Summary</H2>
    <P>
    <CODE>mod_file_cache</CODE> caches a list of statically configured
    files via <CODE>MMapFile</CODE> or <CODE>CacheFile</CODE> directives
    in the main server configuration.
    </P>
  
    <P>
    Not all platforms support both directives. For
    example, Apache on Windows does not currently support the MMapStatic
    directive, while other platforms, like AIX, support both. You will
    receive an error message in the server error log if you attempt to
    use an unsupported directive. If given an unsupported directive, the
    server will start but the file will not be cached. On platforms that
    support both directives, you should experiment with both to see
    which works best for you.
    </P>
  
    <H3><CODE>MmapFile</CODE> Directive </H3>
    <P>
    The <CODE>MmapFile</CODE> directive of <CODE>mod_file_cache</CODE>
    maps a list of statically configured files into memory through the
    system call <CODE>mmap()</CODE>.  This system call is available on
    most modern Unix derivates, but not on all.  There are sometimes
    system-specific limits on the size and number of files that can be
    mmap()d, experimentation is probably the easiest way to find out.
    </P>
    <P>
    This mmap()ing is done once at server start or restart, only. So whenever
    one of the mapped files changes on the filesystem you <EM>have</EM> to
    restart the server (see the <A HREF="../stopping.html">Stopping and
    Restarting</A> documentation).  To reiterate that point:  if the
    files are modified <EM>in place</EM> without restarting the server
    you may end up serving requests that are completely bogus.  You
    should update files by unlinking the old copy and putting a new
    copy in place. Most tools such as <CODE>rdist</CODE> and
    <CODE>mv</CODE> do this. The reason why this modules doesn't take
    care of changes to the files is that this check would need an extra
    <CODE>stat()</CODE> every time which is a waste and against the
    intent of I/O reduction.
    </P>
  
    <H3><CODE>CacheFile</CODE> Directive </H3>
    <P>
    The <CODE>CacheFile</CODE> directive of <CODE>mod_file_cache</CODE>
    opens an active <EM>handle</EM> or <EM>file descriptor</EM> to
the
    file (or files) listed in the configuration directive and places
    these open file handles in the cache.  When the file is requested,
    the server retrieves the handle from the cache and passes it to the
    sendfile() (or TransmitFile() on Windows), socket API. 
    </P>
    <P>
    Insert more details about sendfile API...
    </P>
    <P>
    This file handle caching is done once at server start or restart,
    only. So whenever one of the cached files changes on the filesystem
    you <EM>have</EM> to restart the server (see the <A
    HREF="../stopping.html">Stopping and Restarting</A> documentation).
    To reiterate that point:  if the files are modified <EM>in
    place</EM> without restarting the server you may end up serving
    requests that are completely bogus.  You should update files by
    unlinking the old copy and putting a new copy in place. Most tools
    such as <CODE>rdist</CODE> and <CODE>mv</CODE> do this.
    </P>
  
    <H2>Directives</H2>
    <UL>
     <LI><A HREF="#mmapfile">MMapFile</A>
     </LI>
     <LI><A HREF="#cachefile">CacheFile</A>
     </LI>
    </UL>
  
    <HR>
  
    <H2><A NAME="mmapfile">MMapFile</A></H2>
    <P>
    <A
     HREF="directive-dict.html#Syntax"
     REL="Help"
    ><STRONG>Syntax:</STRONG></A> MMapFile <EM>filename ...</EM>
    <BR>
    <A
     HREF="directive-dict.html#Default"
     REL="Help"
    ><STRONG>Default:</STRONG></A> <EM>None</EM>
    <BR>
    <A
     HREF="directive-dict.html#Context"
     REL="Help"
    ><STRONG>Context:</STRONG></A> server-config
    <BR>
    <A
     HREF="directive-dict.html#Override"
     REL="Help"
    ><STRONG>Override:</STRONG></A> <EM>Not applicable</EM>
    <BR>
    <A
     HREF="directive-dict.html#Status"
     REL="Help"
    ><STRONG>Status:</STRONG></A> Experimental
    <BR>
    <A
     HREF="directive-dict.html#Module"
     REL="Help"
    ><STRONG>Module:</STRONG></A> mod_file_cache
    <BR>
    <A
     HREF="directive-dict.html#Compatibility"
     REL="Help"
    ><STRONG>Compatibility:</STRONG></A> Only in Apache 1.3 (via
    mod_mmap_statis) or later.
  
    <P>
    The <CODE>MMapFile</CODE> directive maps one or more files (given as
    whitespace separated arguments) into memory at server startup time.  They
    are automatically unmapped on a server shutdown. When the files have changed
    on the filesystem at least a HUP or USR1 signal should be send to the server
    to re-mmap them.
    </P>
  
    <P>
    Be careful with the <EM>filename</EM> arguments: They have to literally
    match the filesystem path Apache's URL-to-filename translation handlers
    create. We cannot compare inodes or other stuff to match paths through
    symbolic links <EM>etc.</EM> because that again would cost extra <CODE>stat()</CODE>
    system calls which is not acceptable.  This module may or may not work
    with filenames rewritten by <CODE>mod_alias</CODE> or
    <CODE>mod_rewrite</CODE>.
    </P>
  
    Example:
  
    <PRE>
    MMapFile /usr/local/apache/htdocs/index.html
    </PRE>
  
  
    <H2><A NAME="cachefile">CacheFile</A></H2>
    <P>
    <A
     HREF="directive-dict.html#Syntax"
     REL="Help"
    ><STRONG>Syntax:</STRONG></A> CacheFile <EM>filename ...</EM>
    <BR>
    <A
     HREF="directive-dict.html#Default"
     REL="Help"
    ><STRONG>Default:</STRONG></A> <EM>None</EM>
    <BR>
    <A
     HREF="directive-dict.html#Context"
     REL="Help"
    ><STRONG>Context:</STRONG></A> server-config
    <BR>
    <A
     HREF="directive-dict.html#Override"
     REL="Help"
    ><STRONG>Override:</STRONG></A> <EM>Not applicable</EM>
    <BR>
    <A
     HREF="directive-dict.html#Status"
     REL="Help"
    ><STRONG>Status:</STRONG></A> Experimental
    <BR>
    <A
     HREF="directive-dict.html#Module"
     REL="Help"
    ><STRONG>Module:</STRONG></A> mod_file_cache
    <BR>
    <A
     HREF="directive-dict.html#Compatibility"
     REL="Help"
    ><STRONG>Compatibility:</STRONG></A> Only available in Apache 2.0
or later.
  
    <P>
    The <CODE>CacheFile</CODE> directive opens handles to one or more
    files (given as whitespace separated arguments) and places these
    handles into the cache at server startup time.  Handles to cached
    files are automatically closed on a server shutdown. When the files
    have changed on the filesystem, the server should be restarted to
    to re-cache them.
    </P>
  
    <P>
    Be careful with the <EM>filename</EM> arguments: They have to literally
    match the filesystem path Apache's URL-to-filename translation handlers
    create. We cannot compare inodes or other stuff to match paths through
    symbolic links <EM>etc.</EM> because that again would cost extra <CODE>stat()</CODE>
    system calls which is not acceptable.  This module may or may not work
    with filenames rewritten by <CODE>mod_alias</CODE> or
    <CODE>mod_rewrite</CODE>.
    </P>
  
    Example:
  
    <PRE>
    CacheFile /usr/local/apache/htdocs/index.html
    </PRE>
  
    <P>
    <STRONG>Note</STRONG>: don't bother asking for a for a directive which
    recursively caches all the files in a directory. Try this
    instead... 
    See the <A HREF="core.html#include">Include</A> directive, and consider this
command:
    <PRE>
    find /www/htdocs -type f -print \
    | sed -e 's/.*/mmapfile &amp;/' &gt; /www/conf/mmap.conf
    </PRE>
  
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