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========================
Performance Improvements
========================
------------
Module: core
------------
:Author: Jan Kneschke
:Date: $Date: 2004/11/03 22:26:05 $
:Revision: $Revision: 1.3 $
:abstract:
handling performance issues in lighttpd
.. meta::
:keywords: lighttpd, performance
.. contents:: Table of Contents
Description
===========
Performance Issues
------------------
lighttpd is optimized into varying directions. The most important direction is
performance. The operation system has two major facilities to help lighttpd
a deliver its best performance.
HTTP Keep-Alive
---------------
Disabling keep-alive might help your server if you suffer from a large
number of open file descriptors.
The defaults for the server are: ::
server.max-keep-alive-requests = 128
server.max-keep-alive-idle = 30
server.max-read-idle = 60
server.max-write-idle = 360
handling 128 keep-alive requests in a row on a single connection, waiting 30 seconds
before an unused keep-alive connection gets dropped by lighttpd.
If you handle several connections at once under a high load (let's assume 500 connections
in parallel for 24h) you might run into the out-of-fd problem described below. ::
server.max-keep-alive-requests = 4
server.max-keep-alive-idle = 4
would release the connections earlier and would free file descriptors without a
detrimental performance loss.
Disabling keep-alive completely is the last resort if you are still short on file descriptors: ::
server.max-keep-alive-requests = 0
Event Handlers
--------------
The first one is the Event Handler which takes care of notifying the server
that one of the connections is ready to send or receive. As you can see,
every OS has at least the select() call which has some limitations.
============ ========== ===============
OS Method Config Value
============ ========== ===============
all select select
Unix poll poll
Linux 2.6+ epoll linux-sysepoll
Solaris /dev/poll solaris-devpoll
FreeBSD, ... kqueue freebsd-kqueue
============ ========== ===============
For more information on this topic take a look at http://www.kegel.com/c10k.html
Configuration
`````````````
The event handler can be set by specifying the 'Config Value' from above
in the ``server.event-handler`` variable
e.g.: ::
server.event-handler = "linux-sysepoll"
Network Handlers
----------------
The basic network interface for all platforms at the syscalls read() and
write(). Every modern OS provides its own syscall to help network servers
transfer files as fast as possible.
If you want to send out a file from the webserver, it doesn't make any sense
to copy the file into the webserver just to write() it back into a socket
in the next step.
sendfile() minimizes the work in the application and pushes a file directly
into the network card (ideally).
lighttpd supports all major platform-specific calls:
========== ==========
OS Method
========== ==========
all write
Unix writev
Linux 2.4+ sendfile
Linux 2.6+ sendfile64
Solaris sendfilev
FreeBSD sendfile
========== ==========
The best backend is selected at compile time. In case you want to use
another backend set: ::
server.network-backend = "writev"
You can find more information about network backend in:
https://blog.lighttpd.net/articles/2005/11/11/optimizing-lighty-for-high-concurrent-large-file-downloads
Max Connections
---------------
As lighttpd is a single-threaded server, its main resource limit is the
number of file descriptors, which is set to 1024 by default (on most systems).
If you are running a high-traffic site you might want to increase this limit
by setting ::
server.max-fds = 2048
This only works if lighttpd is started as root.
Out-of-fd condition
-------------------
Since file descriptors are used for TCP/IP sockets, files and directories,
a simple request for a PHP page might result in using 3 file descriptors:
1. the TCP/IP socket to the client
2. the TCP/IP and Unix domain socket to the FastCGI process
3. the filehandle to the file in the document root to check if it exists
If lighttpd runs out of file descriptors, it will stop accepting new
connections for awhile to use the existing file descriptors to handle the
currently-running requests.
If more than 90% of the file descriptors are used then the handling of new
connections is disabled. If it drops below 80% again new connections will
be accepted again.
Under some circumstances you will see ::
... accept() failed: Too many open files
in the error log. This tells you there were too many new requests at once
and lighttpd could not disable the incoming connections soon enough. The
connection was dropped and the client received an error message like 'connection
failed'. This is very rare and might only occur in test setups.
Increasing the ``server.max-fds`` limit will reduce the probability of this
problem.
stat() cache
============
A stat(2) can be expensive; caching it saves time and context switches.
Instead of using stat() every time to check for the existence of a file
you can stat() it once and monitor the directory the file is in for
modifications. As long as the directory doesn't change, the files in it
must all still be the same.
With the help of FAM or gamin you can use kernel events to assure that
your stat cache is up to date. ::
server.stat-cache-engine = "fam" # either fam, simple or disabled
==================
Performance Tuning
==================
[[ Note: latest version is found at https://wiki.lighttpd.net/Docs_Performance ]]
[[ Note: see version with links at https://wiki.lighttpd.net/Docs_Performance ]]
important performance tuning rules
* Prefer lighttpd defaults unless you have a reason to change a setting,
and unless you test that changing the setting is beneficial to you.
* Proper functionality is more important than marginal increases in performance;
a web server that does not function as intended is not useful.
Do not sacrifice security or desired operational functioning for marginal
performance improvements.
* Performance tuning is not magic. The recommended approach is that one change
be made at a time, that the change be tested and benchmarked, and that if the
change does not have a measurable and positive impact in real-world scenarios,
that the change be reverted.
lighttpd is generally pretty snappy.
Most of the following are micro-optimizations.
No changes are required unless you have a specific performance issue that you
must address.
lighttpd configuration performance tuning (technical guidelines)
-----------------------------------------
* less is more (and is often simpler, too)
- rely on defaults where possible to reduce unnecessary (duplicative) config
processing (at runtime) to process configuration directives which were
already set to the default values
- set config options in the global scope rather than repeating in sub-scopes.
lighttpd optimizes configuration settings in the global scope and makes
those settings the defaults
- TLS configuration can be set in the global scope and inherited by multiple
$SERVER["socket"]
ssl.pemfile = "..."
ssl.privkey = "..."
$SERVER["socket"] == ":443" { ssl.engine = "enable" }
$SERVER["socket"] == "[::]:443" { ssl.engine = "enable" }
- list only the modules actually used and enabled in server.modules;
comment out the others
- each loaded module registers itself into lighttpd hooks and gets a chance
to handle each request, which is is unnecessary if a module is loaded but
not otherwise configured to be used
- server.compat-module-load = "disable" skips loading the default modules
(mod_indexfile, mod_dirlisting, mod_staticfile), and you can then
explicitly add one or more to server.modules to use them
- tweaks to remove optional functionality
- server.tag = "" skips sending "Server: lighttpd/1.4.xx" in responses;
alternatively, use: server.tag = "lighttpd" to hide the lighttpd version
- server.range-requests = "disable" can be used if all server responses are
small files, but otherwise it is recommended to be left enabled
- review the default lighttpd config provided by your distro
- configs provided by distros aim to be newbie friendly but can introduce
complexity of yet another config framework
- configs provided by distros are often out-dated and then kept for historic
compatibility, rather than current best practices
- example: ~20 years ago some widely used versions of Adobe Acrobat reader
plugin PDF clients misbehaved with range requests. Unfortunately, the
config setting to disable range requests for PDFs has been cargo-culted
into configs since then. Prefer to comment out or remove:
$HTTP["url"] =~ "\.pdf$" { server.range-requests = "disable" }
- server.max-connections limits the maximum number of simultaneous connections
to handle and also affects memory usage for the connection cache
- default is (about) 1365 which is oversized for all but the largest
systems. Embedded systems might set server.max-connections = 16 or lower
- server.max-worker = 0 should generally be left unset (or "0"), as
CPU bottlenecks are usually elsewhere
- server.follow-symlink = "enable" (default) should be left enabled. If such
restrictions are required, prefer to run a separate lighttp instance under a
separate user account, and enforce more restrictive file access permissions.
- ssl.read-ahead = "disable" (default) is strongly recommended for slower,
embedded systems which process TLS packets more slowly than network
wire-speed. For faster systems, test if ssl.read-ahead = "enable" improves
performance (or not)
- prefer to configure mod_extforward extforward.hap-PROXY for lighttpd
instances behind HAProxy or load balancers supporting the HAProxy PROXY
protocol
* minimize conditional processing (but not at the cost of proper functionality)
- more conditions means more config processing at runtime
- more conditions means more memory used by config per request
- avoid repeating conditions and its opposite by joining them into if/else
<condition> { ... } else { ... }
<condition> { ... } else <condition> { ... } else { ... }
- sometimes it may take fewer config lines to set a config option once in the
global scope and then, where necessary, to unset the option in a small
number of conditions rather than leaving the default in the global scope
and enabling the config option in many more conditions
- having no config conditions will be among the fastest configs to be
processed, but config processing at runtime is fast and is not typically
a bottleneck
* dynamic backends (mod_proxy, mod_fastcgi, mod_scgi, mod_ajp13, ...)
- prefer to use unix domain sockets (instead of TCP sockets) for connections
from lighttpd to backends running on the same host
- lighttpd can listen on a unix domain socket
(server.bind = "/path/to/lighttpd.sock")
and lighttpd mod_proxy can act as a reverse-proxy to a backend lighttpd
server. Use with mod_extforward to preserve client remote address for the
backend.
* mod_fastcgi
- Recommended: use PHP-FPM (FastCGI Process Manager),
which is available as a package in many OS distros
- If not using PHP-FPM, then see Docs_PerformanceFastCGI
- lighttpd provides mechanisms for lighttpd to start up PHP backends, and
that works well, but PHP-FPM is the modern and recommended mechanism to
manage PHP backends
* mod_rewrite and mod_redirect: short-circuiting
(when using a sequence of regexes)
- consider putting static file matches (passed through unmodified) first,
and using a blank target to indicate no modification
- consider using a blank match as a catch-all, rather than "^(.*)",
which will still match all, but without the regex
url.rewrite-once = (
"^/static/|\.(?:css|jpg)$" => "",
"" => "/index.php${url.path}${qsa}"
)
* mod_indexfile: reduce the number of entries in index-file.names,
if mod_indexfile is enabled
- index-file.names = ("index.html") as a list of one or two entries rather
than a list of, say, 10 differenent file extensions
* cache tuning
- stat_cache: default server.stat_cache-engine = "simple" works well for
typical usage and caches stat() results for 1-2 seconds. Test with
server.stat-cache-engine = "inotify" or server.stat-cache-engine = "kqueue"
for stat() results to be cached longer (16 seconds)
- mod_auth: set auth.cache = ("max-age" => "600") to cache passwords (default
disabled), but acknowledge changes to your security posture if enabling the
cache. (since lighttpd 1.4.56)
- mod_deflate: set deflate.cache-dir to cache (and reuse) compressed static
assets based on ETag (since lighttpd 1.4.56)
- mod_dirlisting: set dir-listing.cache = ( ... ) to configure caching of
generated directory listings (since lighttpd 1.4.60)
* do not sacrifice security to save a few CPU cycles
- server.http-parseopts* option defaults are recommended, and are very fast
- disabling server.http-parseopts* might save a few CPU cycles, but is an
anti-pattern for secure configurations
- server.http-parseopts* options should be modified only when the
functionality needs to be tuned for proper site operation
- ETag response headers are used in HTTP/1.1 conditional caching.
ETag response headers are also required for mod_deflate and strongly
recommended with mod_webdav. While lighttpd ETag generation for
static content can be disabled for micro-benchmarking purposes,
ETag generation (default enabled) is recommended for production use
(etag.use-inode, etag.use-mtime, etag.use-size)
* compile lighttpd with mmap support (./configure --enable-mmap) to improve
mod_deflate performance
lighttpd configuration for use of operating system (OS) features
----------------------------------------------------------------
lighttpd generally chooses optimal defaults for the OS on which it is running.
Prefer lighttpd defaults unless something is not functioning correctly.
(Please report bugs and include your platform information if the lighttpd OS
defaults are not working correctly.)
* server.event-handler (e.g. epoll, kqueue, event ports, devpoll, poll, ...)
* server.network-backend (e.g. sendfile, writev, write)
lighttpd configuration tuning for high-traffic sites with a large number of connections
---------------------------------------------------------------------------------------
* test with server.max-fds = 16384 (or higher) and OS system and/or per-user
ulimit -Hn might need to be adjusted to allow this or higher values.
For each 4k increase in server.max-fds, lighttpd uses an additional ~100 kb
of memory for internal structures, not including memory used by each active
connection. (In other words, there is a marginal cost for using very high
values when there are not nearly so many simultaneous open connections).
server.max-connections is calculated to be 1/3 of server.max-fds if
server.max-connections is not configured.
lighttpd configuration tuning for low-memory systems
----------------------------------------------------
* test with server.max-fds = 128 (or lower)
* test with server.max-connections = 16 (or lower)
* test with server.listen-backlog = 16 (or lower)
* (default) server.stat_cache-engine = "simple"
* (default) ssl.read-ahead = "disable"
* support for the HTTP/2 protocol (enabled by default in lighttpd 1.4.59) uses
more memory than HTTP/1.1; low-memory systems might choose to disable HTTP/2
protocol support: server.feature-flags += ("server.h2proto" => "disable")
lighttpd configuration tuning for traffic shapping (download rate-limiting)
--------------------------------------------------
connection.kbytes-per-second
server.kbytes-per-second
lighttpd configuration tuning for timeouts
------------------------------------------
To free up connections more quickly, tune down the idle timeouts for how long
lighttpd waits to read or write to the client (when lighttpd is trying to read
or write), or how long lighttpd waits for the next keep-alive request, and for
how many keep-alive requests, before lighttpd closes the connection. A value
of 0 disables an idle timeout and is not recommended.
* server.max-read-idle = 60
* server.max-write-idle = 360
* server.max-keep-alive-idle = 5
* server.max-keep-alive-requests = 100
Generally, server.max-keep-alive-requests should not be set to 0 since setting
up a new TCP connection takes more resources than keeping an open idle fd,
especially if the connection is over TLS.
Platform-Specific Notes
=======================
Note: The following is old and possibly out-dated.
Please consider only as a starting point for further testing.
Linux
-----

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