lighttpd 1.4.x
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238 lines
7.2 KiB
238 lines
7.2 KiB
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Performance Improvements |
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Module: core |
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:Author: Jan Kneschke |
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:Date: $Date: 2004/11/03 22:26:05 $ |
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:Revision: $Revision: 1.3 $ |
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:abstract: |
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handling performance issues in lighttpd |
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.. meta:: |
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:keywords: lighttpd, performance |
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.. contents:: Table of Contents |
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Description |
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=========== |
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Performance Issues |
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------------------ |
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lighttpd is optimized into varying directions. The most important direction is |
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performance. The operation system has two major facilities to help lighttpd |
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a deliver its best performance. |
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HTTP Keep-Alive |
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--------------- |
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Disabling keep-alive might help your server if you suffer from a large |
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number of open file descriptors. |
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The defaults for the server are: :: |
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server.max-keep-alive-requests = 128 |
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server.max-keep-alive-idle = 30 |
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server.max-read-idle = 60 |
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server.max-write-idle = 360 |
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handling 128 keep-alive requests in a row on a single connection, waiting 30 seconds |
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before an unused keep-alive connection gets dropped by lighttpd. |
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If you handle several connections at once under a high load (let's assume 500 connections |
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in parallel for 24h) you might run into the out-of-fd problem described below. :: |
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server.max-keep-alive-requests = 4 |
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server.max-keep-alive-idle = 4 |
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would release the connections earlier and would free file descriptors without a |
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detrimental performance loss. |
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Disabling keep-alive completely is the last resort if you are still short on file descriptors: :: |
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server.max-keep-alive-requests = 0 |
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Event Handlers |
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-------------- |
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The first one is the Event Handler which takes care of notifying the server |
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that one of the connections is ready to send or receive. As you can see, |
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every OS has at least the select() call which has some limitations. |
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============ ========== =============== |
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OS Method Config Value |
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============ ========== =============== |
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all select select |
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Unix poll poll |
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Linux 2.6+ epoll linux-sysepoll |
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Solaris /dev/poll solaris-devpoll |
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FreeBSD, ... kqueue freebsd-kqueue |
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============ ========== =============== |
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For more information on this topic take a look at http://www.kegel.com/c10k.html |
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Configuration |
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````````````` |
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The event handler can be set by specifying the 'Config Value' from above |
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in the ``server.event-handler`` variable |
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e.g.: :: |
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server.event-handler = "linux-sysepoll" |
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Network Handlers |
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---------------- |
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The basic network interface for all platforms at the syscalls read() and |
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write(). Every modern OS provides its own syscall to help network servers |
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transfer files as fast as possible. |
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If you want to send out a file from the webserver, it doesn't make any sense |
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to copy the file into the webserver just to write() it back into a socket |
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in the next step. |
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sendfile() minimizes the work in the application and pushes a file directly |
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into the network card (ideally). |
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lighttpd supports all major platform-specific calls: |
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========== ========== |
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OS Method |
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========== ========== |
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all write |
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Unix writev |
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Linux 2.4+ sendfile |
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Linux 2.6+ sendfile64 |
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Solaris sendfilev |
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FreeBSD sendfile |
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========== ========== |
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The best backend is selected at compile time. In case you want to use |
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another backend set: :: |
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server.network-backend = "writev" |
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You can find more information about network backend in: |
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https://blog.lighttpd.net/articles/2005/11/11/optimizing-lighty-for-high-concurrent-large-file-downloads |
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Max Connections |
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--------------- |
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As lighttpd is a single-threaded server, its main resource limit is the |
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number of file descriptors, which is set to 1024 by default (on most systems). |
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If you are running a high-traffic site you might want to increase this limit |
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by setting :: |
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server.max-fds = 2048 |
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This only works if lighttpd is started as root. |
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Out-of-fd condition |
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------------------- |
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Since file descriptors are used for TCP/IP sockets, files and directories, |
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a simple request for a PHP page might result in using 3 file descriptors: |
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1. the TCP/IP socket to the client |
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2. the TCP/IP and Unix domain socket to the FastCGI process |
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3. the filehandle to the file in the document root to check if it exists |
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If lighttpd runs out of file descriptors, it will stop accepting new |
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connections for awhile to use the existing file descriptors to handle the |
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currently-running requests. |
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If more than 90% of the file descriptors are used then the handling of new |
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connections is disabled. If it drops below 80% again new connections will |
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be accepted again. |
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Under some circumstances you will see :: |
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... accept() failed: Too many open files |
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in the error log. This tells you there were too many new requests at once |
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and lighttpd could not disable the incoming connections soon enough. The |
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connection was dropped and the client received an error message like 'connection |
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failed'. This is very rare and might only occur in test setups. |
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Increasing the ``server.max-fds`` limit will reduce the probability of this |
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problem. |
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stat() cache |
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============ |
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A stat(2) can be expensive; caching it saves time and context switches. |
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Instead of using stat() every time to check for the existence of a file |
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you can stat() it once and monitor the directory the file is in for |
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modifications. As long as the directory doesn't change, the files in it |
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must all still be the same. |
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With the help of FAM or gamin you can use kernel events to assure that |
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your stat cache is up to date. :: |
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server.stat-cache-engine = "fam" # either fam, simple or disabled |
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Platform-Specific Notes |
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======================= |
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Linux |
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----- |
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For Linux 2.4.x you should think about compiling lighttpd with the option |
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``--disable-lfs`` to disable the support for files larger than 2GB. lighttpd will |
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fall back to the ``writev() + mmap()`` network calls which is ok, but not as |
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fast as possible but support files larger than 2GB. |
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Disabling the TCP options reduces the overhead of each TCP packet and might |
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help to get the last few percent of performance out of the server. Be aware that |
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disabling these options most likely decreases performance for high-latency and lossy |
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links. |
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- net.ipv4.tcp_sack = 0 |
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- net.ipv4.tcp_timestamps = 0 |
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Increasing the TCP send and receive buffers will increase the performance a |
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lot if (and only if) you have a lot of large files to send. |
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- net.ipv4.tcp_wmem = 4096 65536 524288 |
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- net.core.wmem_max = 1048576 |
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If you have a lot of large file uploads, increasing the receive buffers will help. |
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- net.ipv4.tcp_rmem = 4096 87380 524288 |
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- net.core.rmem_max = 1048576 |
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Keep in mind that every TCP connection uses the configured amount of memory for socket |
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buffers. If you've got many connections this can quickly drain the available memory. |
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See http://www.acc.umu.se/~maswan/linux-netperf.txt for more information on these parameters. |
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FreeBSD |
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------- |
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On FreeBSD you might gain some performance by enabling accept filters. Just |
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compile your kernel with: :: |
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options ACCEPT_FILTER_HTTP |
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For more ideas about tuning FreeBSD read: tuning(7) |
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Reducing the recvspace should always be ok if the server only handles HTTP |
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requests without large uploads. Increasing the sendspace would reduce the |
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system load if you have a lot of large files to be sent, but keep in mind that |
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you have to provide the memory in the kernel for each connection. 1024 * 64KB |
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would mean 64MB of kernel RAM. Keep this in mind. |
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- net.inet.tcp.recvspace = 4096 |
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