diff options
| author |   hongbotian <hongbo.tianhongbo@huawei.com> | 2015-11-30 03:10:21 -0500 |
|---|---|---|
| committer | hongbotian <hongbo.tianhongbo@huawei.com> | 2015-11-30 03:10:21 -0500 |
| commit | c0b7206652b2852bc574694e7ba07ba1c2acdc00 (patch) | |
| tree | 5cb95cb0e19e03610525903df46279df2c3b7eb1 /rubbos/app/apache2/manual/misc/fin_wait_2.html.en | |
| parent | b6d3d6e668b793220f2d3af1bc3e828553dc3fe6 (diff) | |
delete app
Change-Id: Id4c572809969ebe89e946e88063eaed262cff3f2
Signed-off-by: hongbotian <hongbo.tianhongbo@huawei.com>
Diffstat (limited to 'rubbos/app/apache2/manual/misc/fin_wait_2.html.en')
| -rw-r--r-- | rubbos/app/apache2/manual/misc/fin_wait_2.html.en | 422 |
1 files changed, 0 insertions, 422 deletions
diff --git a/rubbos/app/apache2/manual/misc/fin_wait_2.html.en b/rubbos/app/apache2/manual/misc/fin_wait_2.html.en deleted file mode 100644 index 60da4b0d..00000000 --- a/rubbos/app/apache2/manual/misc/fin_wait_2.html.en +++ /dev/null @@ -1,422 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> -<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - This file is generated from xml source: DO NOT EDIT - XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX - --> -<title>Connections in the FIN_WAIT_2 state and Apache - Apache HTTP Server</title> -<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /> -<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /> -<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /> -<link href="../images/favicon.ico" rel="shortcut icon" /></head> -<body id="manual-page"><div id="page-header"> -<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p> -<p class="apache">Apache HTTP Server Version 2.0</p> -<img alt="" src="../images/feather.gif" /></div> -<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div> -<div id="path"> -<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Miscellaneous Documentation</a></div><div id="page-content"><div id="preamble"><h1>Connections in the FIN_WAIT_2 state and Apache</h1> -<div class="toplang"> -<p><span>Available Languages: </span><a href="../en/misc/fin_wait_2.html" title="English"> en </a></p> -</div> - - - <div class="warning"><h3>Warning:</h3> - <p>This document has not been fully updated - to take into account changes made in the 2.0 version of the - Apache HTTP Server. Some of the information may still be - relevant, but please use it with care.</p> - </div> - - <p>Starting with the Apache 1.2 betas, people are reporting - many more connections in the FIN_WAIT_2 state (as reported - by <code>netstat</code>) than they saw using older - versions. When the server closes a TCP connection, it sends - a packet with the FIN bit set to the client, which then - responds with a packet with the ACK bit set. The client - then sends a packet with the FIN bit set to the server, - which responds with an ACK and the connection is closed. - The state that the connection is in during the period - between when the server gets the ACK from the client and - the server gets the FIN from the client is known as - FIN_WAIT_2. See the <a href="ftp://ds.internic.net/rfc/rfc793.txt">TCP RFC</a> for - the technical details of the state transitions.</p> - - <p>The FIN_WAIT_2 state is somewhat unusual in that there - is no timeout defined in the standard for it. This means - that on many operating systems, a connection in the - FIN_WAIT_2 state will stay around until the system is - rebooted. If the system does not have a timeout and too - many FIN_WAIT_2 connections build up, it can fill up the - space allocated for storing information about the - connections and crash the kernel. The connections in - FIN_WAIT_2 do not tie up an httpd process.</p> - - </div> -<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#why">Why Does It Happen?</a></li> -<li><img alt="" src="../images/down.gif" /> <a href="#what">What Can I Do About it?</a></li> -<li><img alt="" src="../images/down.gif" /> <a href="#appendix">Appendix</a></li> -</ul></div> -<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="why" id="why">Why Does It Happen?</a></h2> - - <p>There are numerous reasons for it happening, some of them - may not yet be fully clear. What is known follows.</p> - - <h3><a name="buggy" id="buggy">Buggy Clients and Persistent - Connections</a></h3> - - <p>Several clients have a bug which pops up when dealing with - persistent connections (aka - keepalives). When the connection is idle and the server - closes the connection (based on the <code class="directive"><a href="../mod/core.html#keepalivetimeout">KeepAliveTimeout</a></code>), - the client is programmed so that the client does not send - back a FIN and ACK to the server. This means that the - connection stays in the FIN_WAIT_2 state until one of the - following happens:</p> - - <ul> - <li>The client opens a new connection to the same or a - different site, which causes it to fully close the older - connection on that socket.</li> - - <li>The user exits the client, which on some (most?) - clients causes the OS to fully shutdown the - connection.</li> - - <li>The FIN_WAIT_2 times out, on servers that have a - timeout for this state.</li> - </ul> - - <p>If you are lucky, this means that the buggy client will - fully close the connection and release the resources on - your server. However, there are some cases where the socket - is never fully closed, such as a dialup client - disconnecting from their provider before closing the - client. In addition, a client might sit idle for days - without making another connection, and thus may hold its - end of the socket open for days even though it has no - further use for it. <strong>This is a bug in the browser or - in its operating system's TCP implementation.</strong></p> - - <p>The clients on which this problem has been verified to - exist:</p> - - <ul> - <li>Mozilla/3.01 (X11; I; FreeBSD 2.1.5-RELEASE - i386)</li> - - <li>Mozilla/2.02 (X11; I; FreeBSD 2.1.5-RELEASE - i386)</li> - - <li>Mozilla/3.01Gold (X11; I; SunOS 5.5 sun4m)</li> - - <li>MSIE 3.01 on the Macintosh</li> - - <li>MSIE 3.01 on Windows 95</li> - </ul> - - <p>This does not appear to be a problem on:</p> - - <ul> - <li>Mozilla/3.01 (Win95; I)</li> - </ul> - - <p>It is expected that many other clients have the same - problem. What a client <strong>should do</strong> is - periodically check its open socket(s) to see if they have - been closed by the server, and close their side of the - connection if the server has closed. This check need only - occur once every few seconds, and may even be detected by a - OS signal on some systems (<em>e.g.</em>, Win95 and NT - clients have this capability, but they seem to be ignoring - it).</p> - - <p>Apache <strong>cannot</strong> avoid these FIN_WAIT_2 - states unless it disables persistent connections for the - buggy clients, just like we recommend doing for Navigator - 2.x clients due to other bugs. However, non-persistent - connections increase the total number of connections needed - per client and slow retrieval of an image-laden web page. - Since non-persistent connections have their own resource - consumptions and a short waiting period after each closure, - a busy server may need persistence in order to best serve - its clients.</p> - - <p>As far as we know, the client-caused FIN_WAIT_2 problem - is present for all servers that support persistent - connections, including Apache 1.1.x and 1.2.</p> - - - - <h3><a name="code" id="code">A necessary bit of code - introduced in 1.2</a></h3> - - <p>While the above bug is a problem, it is not the whole - problem. Some users have observed no FIN_WAIT_2 problems - with Apache 1.1.x, but with 1.2b enough connections build - up in the FIN_WAIT_2 state to crash their server. The most - likely source for additional FIN_WAIT_2 states is a - function called <code>lingering_close()</code> which was - added between 1.1 and 1.2. This function is necessary for - the proper handling of persistent connections and any - request which includes content in the message body - (<em>e.g.</em>, PUTs and POSTs). What it does is read any - data sent by the client for a certain time after the server - closes the connection. The exact reasons for doing this are - somewhat complicated, but involve what happens if the - client is making a request at the same time the server - sends a response and closes the connection. Without - lingering, the client might be forced to reset its TCP - input buffer before it has a chance to read the server's - response, and thus understand why the connection has - closed. See the <a href="#appendix">appendix</a> for more - details.</p> - - <p>The code in <code>lingering_close()</code> appears to - cause problems for a number of factors, including the - change in traffic patterns that it causes. The code has - been thoroughly reviewed and we are not aware of any bugs - in it. It is possible that there is some problem in the BSD - TCP stack, aside from the lack of a timeout for the - FIN_WAIT_2 state, exposed by the - <code>lingering_close</code> code that causes the observed - problems.</p> - - - </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="what" id="what">What Can I Do About it?</a></h2> - - <p>There are several possible workarounds to the problem, some - of which work better than others.</p> - - <h3><a name="add_timeout" id="add_timeout">Add a timeout for FIN_WAIT_2</a></h3> - - <p>The obvious workaround is to simply have a timeout for the - FIN_WAIT_2 state. This is not specified by the RFC, and - could be claimed to be a violation of the RFC, but it is - widely recognized as being necessary. The following systems - are known to have a timeout:</p> - - <ul> - <li><a href="http://www.freebsd.org/">FreeBSD</a> - versions starting at 2.0 or possibly earlier.</li> - - <li><a href="http://www.netbsd.org/">NetBSD</a> version - 1.2(?)</li> - - <li><a href="http://www.openbsd.org/">OpenBSD</a> all - versions(?)</li> - - <li><a href="http://www.bsdi.com/">BSD/OS</a> 2.1, with - the <a href="ftp://ftp.bsdi.com/bsdi/patches/patches-2.1/K210-027"> - K210-027</a> patch installed.</li> - - <li><a href="http://www.sun.com/">Solaris</a> as of - around version 2.2. The timeout can be tuned by using - <code>ndd</code> to modify - <code>tcp_fin_wait_2_flush_interval</code>, but the - default should be appropriate for most servers and - improper tuning can have negative impacts.</li> - - <li><a href="http://www.linux.org/">Linux</a> 2.0.x and - earlier(?)</li> - - <li><a href="http://www.hp.com/">HP-UX</a> 10.x defaults - to terminating connections in the FIN_WAIT_2 state after - the normal keepalive timeouts. This does not refer to the - persistent connection or HTTP keepalive timeouts, but the - <code>SO_LINGER</code> socket option which is enabled by - Apache. This parameter can be adjusted by using - <code>nettune</code> to modify parameters such as - <code>tcp_keepstart</code> and <code>tcp_keepstop</code>. - In later revisions, there is an explicit timer for - connections in FIN_WAIT_2 that can be modified; contact - HP support for details.</li> - - <li><a href="http://www.sgi.com/">SGI IRIX</a> can be - patched to support a timeout. For IRIX 5.3, 6.2, and 6.3, - use patches 1654, 1703 and 1778 respectively. If you have - trouble locating these patches, please contact your SGI - support channel for help.</li> - - <li><a href="http://www.ncr.com/">NCR's MP RAS Unix</a> - 2.xx and 3.xx both have FIN_WAIT_2 timeouts. In 2.xx it - is non-tunable at 600 seconds, while in 3.xx it defaults - to 600 seconds and is calculated based on the tunable - "max keep alive probes" (default of 8) multiplied by the - "keep alive interval" (default 75 seconds).</li> - - <li><a href="http://www.sequent.com">Sequent's ptx/TCP/IP - for DYNIX/ptx</a> has had a FIN_WAIT_2 timeout since - around release 4.1 in mid-1994.</li> - </ul> - - <p>The following systems are known to not have a - timeout:</p> - - <ul> - <li><a href="http://www.sun.com/">SunOS 4.x</a> does not - and almost certainly never will have one because it as at - the very end of its development cycle for Sun. If you - have kernel source should be easy to patch.</li> - </ul> - - <p>There is a <a href="http://www.apache.org/dist/httpd/contrib/patches/1.2/fin_wait_2.patch"> - patch available</a> for adding a timeout to the FIN_WAIT_2 - state; it was originally intended for BSD/OS, but should be - adaptable to most systems using BSD networking code. You - need kernel source code to be able to use it.</p> - - - - <h3><a name="no_lingering" id="no_lingering">Compile without using - <code>lingering_close()</code></a></h3> - - <p>It is possible to compile Apache 1.2 without using the - <code>lingering_close()</code> function. This will result - in that section of code being similar to that which was in - 1.1. If you do this, be aware that it can cause problems - with PUTs, POSTs and persistent connections, especially if - the client uses pipelining. That said, it is no worse than - on 1.1, and we understand that keeping your server running - is quite important.</p> - - <p>To compile without the <code>lingering_close()</code> - function, add <code>-DNO_LINGCLOSE</code> to the end of the - <code>EXTRA_CFLAGS</code> line in your - <code>Configuration</code> file, rerun - <code class="program"><a href="../programs/Configure.html">Configure</a></code> and rebuild the server.</p> - - - - <h3><a name="so_linger" id="so_linger">Use <code>SO_LINGER</code> as - an alternative to <code>lingering_close()</code></a></h3> - - <p>On most systems, there is an option called - <code>SO_LINGER</code> that can be set with - <code>setsockopt(2)</code>. It does something very similar - to <code>lingering_close()</code>, except that it is broken - on many systems so that it causes far more problems than - <code>lingering_close</code>. On some systems, it could - possibly work better so it may be worth a try if you have - no other alternatives.</p> - - <p>To try it, add <code>-DUSE_SO_LINGER - -DNO_LINGCLOSE</code> to the end of the - <code>EXTRA_CFLAGS</code> line in your - <code>Configuration</code> file, rerun - <code class="program"><a href="../programs/Configure.html">Configure</a></code> and rebuild the server.</p> - - <div class="note"><h3>NOTE</h3>Attempting to use - <code>SO_LINGER</code> and <code>lingering_close()</code> - at the same time is very likely to do very bad things, so - don't.</div> - - - - <h3><a name="increase_mem" id="increase_mem">Increase the amount of memory - used for storing connection state</a></h3> - - <dl> - <dt>BSD based networking code:</dt> - - <dd> - BSD stores network data, such as connection states, in - something called an mbuf. When you get so many - connections that the kernel does not have enough mbufs - to put them all in, your kernel will likely crash. You - can reduce the effects of the problem by increasing the - number of mbufs that are available; this will not - prevent the problem, it will just make the server go - longer before crashing. - - <p>The exact way to increase them may depend on your - OS; look for some reference to the number of "mbufs" or - "mbuf clusters". On many systems, this can be done by - adding the line <code>NMBCLUSTERS="n"</code>, where - <code>n</code> is the number of mbuf clusters you want - to your kernel config file and rebuilding your - kernel.</p> - </dd> - </dl> - - - - <h3><a name="disable" id="disable">Disable KeepAlive</a></h3> - - <p>If you are unable to do any of the above then you - should, as a last resort, disable KeepAlive. Edit your - httpd.conf and change "KeepAlive On" to "KeepAlive - Off".</p> - - - </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div> -<div class="section"> -<h2><a name="appendix" id="appendix">Appendix</a></h2> - - <p>Below is a message from Roy Fielding, one of the authors - of HTTP/1.1.</p> - - <h3><a name="message" id="message">Why the lingering close - functionality is necessary with HTTP</a></h3> - - <p>The need for a server to linger on a socket after a close - is noted a couple times in the HTTP specs, but not - explained. This explanation is based on discussions between - myself, Henrik Frystyk, Robert S. Thau, Dave Raggett, and - John C. Mallery in the hallways of MIT while I was at W3C.</p> - - <p>If a server closes the input side of the connection - while the client is sending data (or is planning to send - data), then the server's TCP stack will signal an RST - (reset) back to the client. Upon receipt of the RST, the - client will flush its own incoming TCP buffer back to the - un-ACKed packet indicated by the RST packet argument. If - the server has sent a message, usually an error response, - to the client just before the close, and the client - receives the RST packet before its application code has - read the error message from its incoming TCP buffer and - before the server has received the ACK sent by the client - upon receipt of that buffer, then the RST will flush the - error message before the client application has a chance to - see it. The result is that the client is left thinking that - the connection failed for no apparent reason.</p> - - <p>There are two conditions under which this is likely to - occur:</p> - - <ol> - <li>sending POST or PUT data without proper - authorization</li> - - <li>sending multiple requests before each response - (pipelining) and one of the middle requests resulting in - an error or other break-the-connection result.</li> - </ol> - - <p>The solution in all cases is to send the response, close - only the write half of the connection (what shutdown is - supposed to do), and continue reading on the socket until - it is either closed by the client (signifying it has - finally read the response) or a timeout occurs. That is - what the kernel is supposed to do if SO_LINGER is set. - Unfortunately, SO_LINGER has no effect on some systems; on - some other systems, it does not have its own timeout and - thus the TCP memory segments just pile-up until the next - reboot (planned or not).</p> - - <p>Please note that simply removing the linger code will - not solve the problem -- it only moves it to a different - and much harder one to detect.</p> - - </div></div> -<div class="bottomlang"> -<p><span>Available Languages: </span><a href="../en/misc/fin_wait_2.html" title="English"> en </a></p> -</div><div id="footer"> -<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> -<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div> -</body></html>
\ No newline at end of file |