Docs PerformanceFastCGI » History » Revision 18
Revision 17 (Anonymous, 2006-12-20 08:47) → Revision 18/31 (Anonymous, 2007-02-11 23:37)
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Optimizing FastCGI performance
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.. contents::
Overview
========
If you've recently asked yourself you lately ran into the questions
* "How many PHP backends do I need for my load?" load" or
* "Why is my application returning an the error 500 from time to time?" time"
then you'll you want to read this article very carefully.
How many PHP processes php-process do I need? need ?
================================= ================================
That's the question you're looking for the answer to, why you are here I think and to answer it, it's probably easiest to use an example. it let me create a small example:
lighty is managing a pipe. On one side are your users with their web browsers, webbrowsers, on the other side is PHP. If In case
you have more incoming requests than your backends can handle, lighty will queue them up and will push the new
requests to the backends when they are free again. If you have so many requests that the queue still fills up, it will burst and the next
requests to this backend will be denied, and you'll denied. You will see a message in the error log errorlog like this: ::
... load = 380 ...
To come up with a formula to calculate the number of backends you need, consider this: need think of:
* you have 100 PHP requests per second php-req/s
* the average request time request-time on the PHP side is 0.1sec 0.1s
In the average case you need: ::
100 PHP requests/sec php-reqs/s * 0.1sec/PHP request 0.1s/php-req = 10 PHP processes php-procs
Since You see ? As you probably propably can't control the number of incoming PHP requests, the best PHP-requests, you can do is to reduce only tune the average
request time spent in the PHP process. Some ideas:
* Use a byte-code cache like http://xcache.lighttpd.net/ or http://pecl.php.net/APC
* Add add caching to your application
* Tune tune your queries to the database queries
Measuring As measuring the average request time is not that easy, so output like "fastcgi.backend.0.load: 22" easy the (fastcgi.backend.0.load: 22) is an your indicator
of how many PHP processes php-process would be used right now.
Measuring the load
==================
Load the status-module and enable the statistics: ::
server.modules = {..., "mod_status", ... }
status.statistics-url = "/server-counters"
The counters page lists serveral counters of the fastcgi module:
* the total over all number of requests handled handle by the module
* the total number of currently waiting requests waiting to be handled
* the number of requests currently waiting to be handled request per backend
.. note::
If you have more than one backend, backend you should name each backend individually. ::
fastcgi.server = (
".php" => (
"backend1" => ( "host" => "php-srv1", ... ),
"backend2" => ( "host" => "php-srv2", ... ),
)
)
You might get this output: ::
fastcgi.active-requests: 22
fastcgi.backend.0.0.connected: 5639
fastcgi.backend.0.0.died: 0
fastcgi.backend.0.0.disabled: 0
fastcgi.backend.0.0.load: 11
fastcgi.backend.0.0.overloaded: 0
fastcgi.backend.0.1.connected: 7724
fastcgi.backend.0.1.died: 0
fastcgi.backend.0.1.disabled: 0
fastcgi.backend.0.1.load: 11
fastcgi.backend.0.1.overloaded: 0
fastcgi.backend.0.load: 22
fastcgi.requests: 13363
We have 2 backends (max-procs = 2) and a current load of 22 (fastcgi.backend.0.load: 22). The load is equally
distributed over the two backends (fastcgi.backend.0.0.load: 11, fastcgi.backend.0.1.load: 11).
Using rrdtool to monitor the load
---------------------------------
Enable mod_rrdtool in your config, and add the following config entries (adapt these to your actual setup): ::
rrdtool.binary = "/usr/bin/rrdtool"
rrdtool.db-name = "/var/www/lighttpd/lighttpd-web.rrd"
Read the documentation on rrd on how to generate a graph from the .rrd file.
Installing XCache
=================
XCache is one of the cachers that speeds speed up your fastcgi processing in case you're using PHP. Pick the lastest version from http://trac.lighttpd.net/xcache/wiki/ReleaseArchive.
To install: ::
~/src $ wget http://... (the release url)
~/src $ tar -zxf xcache-*.tar.gz
~/src $ cd xcache
~/src/xcache $ phpize
~/src/xcache $ ./configure --enable-xcache --enable-xcache-coverager
~/src/xcache $ make
~/src/xcache $ su
~/src/xcache # make install
~/src/xcache # cat xcache.ini >> /etc/php.ini
~/src/xcache # $EDITOR /etc/php.ini
Set turn xcache.size=64M, and set up setup your xcache.admin.pass.
Setting up the web interface: ::
alias.url += ("/xcache-admin/" => "/usr/share/xcache/admin/")
Check it out by pointing your browser to http://localhost/xcache-admin/
Tuning the database
===================
This is a very short intro to tuning MySQL. First check your my.cnf:
.. note::
*Read up before changing anything on your server, server especially if you are not on a dedicated MySQL box with spare memory.* memory*
::
[mysqld]
## default is 100, might need to raise it
max-connections = 200
## if you use innodb alot, increase the pool-size
## default is 8M, far too low.
innodb_buffer_pool_size = 512M
## for MyISAM it is
key_buffer_size = 128M
query_cache_size = 32M
## logs are good
log-slow-queries
long-query-time = 2
log-queries-not-using-indexes
Restart the MySQL server and check for 'hostname-slow.log' in the datadir. It will list all queries which
* take longer than 2 seconds to execute, or execute
* are not using an index
On all these queries, queries run an a EXPLAIN and add an a index when necessary. You'll neccesary. You want to concentrate on queries which
* are run often, or
often
* have a query-time > 2
If the number of examined rows is several times larger than the number of sent rows, sent-rows, add an index.
Another thing What you want to check for too is: ::
mysql> SHOW GLOBAL STATUS;
...
| Created_tmp_disk_tables | 88 |
| Created_tmp_files | 2 |
| Created_tmp_tables | 39079 |
...
Created_tmp_disk_tables should as small as
possible compared to Created_tmp_tables
| Com_select | 39004 |
| Select_scan | 39004 |
Oops, Ooops, all SELECT statements are Table-Scans, very bad.
...
| Table_locks_immediate | 3 |
| Table_locks_waited | 0 |
This is good, we never had to wait for a table lock. table-lock.
.. note::
In MySQL before 5.0.x it is SHOW STATUS.
Benchmarking
============
By measuring the response time before and after the optimizations, optimizations you can get an a idea of how an a increased load
will affect effect you in the future.
Several tools are available to measure the response time: response-time:
* ab/ab2 is part of the Apache Server package
* handles max 1024 connections
* hammers a single URL only
* is select()-based select() based
* flood is an a apache project
* siege
* handles about 100 parallel connections (before it dies duo to lack of memory) here with out-of-memory)
* is threaded
* can generate random load
* http_load
* can generate random load
* allows allow throttling
* httpperf
When you are using a benchmark tool which only queries a single URL several times, you won't see problems caused by:
* dirty caches (MySQL Query Cache, Byte-Code Cache, ...)
* locking (Table Locks, File Locks, ...)
If you use siege for the random load and ab for the single-URL load, you should get useful results.
(to be continued)
Can I have too many PHP processes? php-processes ?
================================== ===================================
Having too many PHP processes can be bad too. If you have more than you need, the PHP processes will use up eat all the available memory
and will start using your swap space, which is much slower than real memory. hit the swap-space.
If you are using a config like this: like: ::
fastcgi.server = ( ".php" =>
(( "socket" => "/tmp/php-fastcgi.socket",
"bin-path" => "/usr/bin/php-cgi",
"max-procs" => 10,
"bin-environment" => (
"PHP_FCGI_CHILDREN" => "16",
"PHP_FCGI_MAX_REQUESTS" => "1000"
),
"broken-scriptfilename" => "enable"
))
)
you will have (following the famous formula):: formular)::
num-procs = max-procs * ( 1 + PHP_FCGI_CHILDREN )
10 * (16 + 1) = 170 procs
A single Together with a PHP 5.1.5 process running with APC 3.0.11 a single PHP process takes about 13MB 13Mb (RSZ) for itself: ::
$ ps axu | grep php
400 web 16 0 152m 13m 6804 S 1 0.7 0:01.99 php-fcgi
13MB 13M * 160 processes = 2GB 2Gb RAM
Not all of them will be using 13MB right 13m from the start, but you start to see the problem. problem I think. Running into swap space is counter-productive.
Remote Balancing
================
If all this doesn't help, help you can still take a few servers, install a shared filesystem file-system like NFS and run
PHP on these this servers. Just add their the IPs to the "host" field in the fastcgi.server setting and lighty
will balance the load across the PHP of those servers.
I use Perl, Ruby, Python, or another language ...
============================================= =============================
PHP was only used as an example. Most of these suggestions apply The same applies to other languages as well. all languages.
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