===================================================
 Horde Groupware Webmail Edition Performance Guide
===================================================

:Contact: horde@lists.horde.org

.. contents:: Contents


Some tips on performance tuning systems for Horde Groupware Webmail Edition.
This does not cover hardware tuning or even low level system (network,
filesystem, etc) tuning.

Don't apply the following tuning hints blindly.  Test your applications before
and after the changes under the conditions that are important for you.  For
some people it's more important to make them as fast as possible for a small
user base, others require the applications to scale well under a high load.
Some of these hints might even make the applications slower under certain
conditions or using a certain hardware.


Linux Tuning
============

* Recompile RPMS for your architecture (e.g. i586, i686, athlon, etc).
  This applies most to your Apache, PHP, IMAP, and POP3 packages.


Webserver/PHP tuning
====================

* Consider a PHP accelerator program.  See for example `The Zend Performance
  Suite`_, the `Alternative PHP Cache`_, eAccelerator_, or XCache_.  These
  accelerators speed up access by caching the compiled PHP code, eliminating
  the need to recompile the code for every single page load. **This is probably
  the easiest way to improve the performance of Horde Groupware Webmail
  Edition**. See Autoloading_ further down to get even more out of some of
  those accelerators.

* Enable PHP output compression in the Horde configuration. Do not enable
  compression in the PHP configuration (i.e. in ``php.ini``), because certain
  scripts don't work well with compression and Horde Groupware Webmail Edition
  takes care of disabling compression conditionally.

* Keep the include path defined in ``php.ini`` as short as possible, with the
  most frequently used library paths first.  You don't need to include the
  local directory ``.`` because Horde Groupware Webmail Edition always uses
  full paths instead of relative paths.

* Use an optimized ``php.ini``: start with ``php.ini-recommended`` in your PHP
  dsitribution.

* Don't run PHP session garbage collection too often if using a slow storage
  medium (like SQL). (See ``session.gc_probability`` in ``php.ini``)

* If you have a large number of sessions and are using PHP's default file
  based session handler, consider storing them in hashed directory levels.
  (See ``session.save_path`` at http://www.php.net/session)

* Consider using a faster storage medium for sessions, such as a tmpfs
  (if storing sessions locally) or memcache (for storing session information
  that can be accessed by multiple servers).

* Only load as many Apache and PHP extensions as needed (to reduce memory
  usage).

* Use statically compiled Apache modules, including the PHP module.

* Use compiler optimizations (--prefer-non-pic, -O3, -march -mcpu, -msse,
  -mmmx, -mfpmath=sse, etc.)

* If using SSL with a large site, consider a hardware SSL accelerator.

* Use shared memory for the Apache SSL cache if possible.

* To improve caching of static content if accessing Apache SSL with Internet
  Explorer, try setting longer expiration periods::

    ExpiresActive On
    ExpiresByType image/png "now plus 1 month"
    ExpiresByType image/gif "now plus 1 month"
    ExpiresByType text/javascript "now plus 1 month"
    ExpiresByType application/x-javascript "now plus 1 month"
    ExpiresByType text/css "now plus 1 month"

  .. Note:: You must compile the ``mod_expires`` extension into Apache in
            order to use these directives.

  .. Warning:: This might cause problems if you upgrade Horde Groupware
               Webmail Edition and the users' browsers still use the old file
               versions.

* Disable DNS lookups in your Apache logging, or use a caching DNS server on
  the web server host.

  Horde itself will run DNS queries too, so make sure your DNS resolution works
  correctly and fast.

* Enable Apache keepalives.

* You can configure Horde to serve all images, style sheets and/or static
  javascript files from a different server. This could be a very lightweight
  server without PHP (and other CGI modules) builtin. If using SSL to serve
  all pages, the images/js server will also have to serve SSL content or else
  browsers will complain about non-secure content in a secure page. Since this
  server does not need to handle dynamic content, it would be wise to use a
  high-performance server with low memory and/or system resource requirements
  (this `IBM Article`_ can provide further information). You need to set
  the ``themesuri`` and/or ``jsuri`` parameters in ``config/registry.php`` for
  all applications and copy all ``themes`` and/or ``js`` directories in the
  same directory layout to the other server.

* Your webserver should use Expires headers to make sure static content can
  be cached on the user's browser.  For example, to make lighttpd set an
  expiration date on all graphics, javascript files, and stylesheets, add
  the following to ``lighttpd.conf``::

    $HTTP["url"] =~ "\.(jpg|gif|png|js|css)$" {
        expire.url = ( "" => "access 1 months" )
    }

* Enable caching in Horde Groupware. Several applications make heavy use of
  caching and, if enabled, you will see a significant increase in performance.

* Enable caching/compression of javascript and CSS. See `Yahoo's Analysis`_
  which concludes that "[r]educing the number of HTTP requests has the biggest
  impact on reducing response time". Caching via filesystem is HIGHLY
  RECOMMENDED: it is also the only way of caching that reliably works on all
  browsers. Caching can also be done via horde caching, but the
  cache-busters used to generate unique URLs when the cached content changes
  do not work 100% reliably across all browsers.

* It is highly recommended to install the lzf PECL module to activate
  compression for certain Horde data (especially in IMP).  lzf is a tiny
  module that does real-time compression.  The lzf documentation states that on
  modern CPUs, compression is as fast as an (unoptimized) memcpy action, making
  the compression essentially 'free' when compared to uncompressed data.
  lzf can be installed via PECL (see INSTALL).

.. _`The Zend Performance Suite`: http://www.zend.com/horde.php
.. _`Alternative PHP Cache`: http://www.php.net/apc
.. _eAccelerator: http://eaccelerator.net/
.. _XCache: http://xcache.lighttpd.net/
.. _`IBM Article`: http://www.ibm.com/developerworks/web/library/wa-ltwebserv/
.. _`Yahoo's Analysis`: http://yuiblog.com/blog/2006/11/28/performance-research-part-1/


Sending Mail
============

* Generally using a local sendmail command to send mail will result in better
  peformance than using a SMTP connection.

* Some MTA servers may be faster or more efficient than others.  Consider
  switching to a faster format if needed.


IMAP tuning
===========

* Consider an IMAP proxy to allow persistent connections.

  imapproxy_ is HIGHLY RECOMMENDED - especially versions 1.2.7rc1 and greater
  which contains features used internally by Horde Groupware Webmail Edition to
  speed up access to the remote server.

  NOTE: if your installation connects to multiple imapproxy instances, you MUST
  configure your Horde Groupware Webmail Edition installation to persistently
  connect to a single backend over the course of a session. If this is not
  possible, you must remove support for imapproxy's advanced features by adding
  'XIMAPPROXY' to the 'capability_ignore' parameter in your local
  configuration.

* Use an IMAP server that supports CONDSTORE (RFC 4551) and/or QRESYNC (RFC
  5162).

  These extensions are required to properly cache data and to properly keep the
  dynamic display synchronized. It is impossible to do otherwise, and the UI
  experience will be limited without these extensions. Additionally, if these
  IMAP extensions are available, Horde Groupware Webmail Edition is able to
  cache servers which signficantly saves on client/server IMAP interactions.

  Technical information can be found here:

  http://lists.horde.org/archives/imp/Week-of-Mon-20110523/052285.html

* Some IMAP servers perform better than others. The Horde Project recommends
  either Cyrus_ or Dovecot_ as these servers are actively developed, implement
  advanced IMAP protocols, and use server-side caching to speed performance.

* Consider switching to a faster mailbox storage format if needed. This may
  also require switching the underlying filesystem.

  Further information can be found here:

  http://wiki2.dovecot.org/MailboxFormat

* Follow the IMAP servers' performance hints:

  - Cyrus: http://git.cyrusimap.org/cyrus-imapd/tree/doc/install-perf.html
  - Dovecot: http://wiki.dovecot.org/PerformanceTuning

.. _Cyrus: http://www.cyrusimap.org/
.. _Dovecot: http://www.dovecot.org/
.. _imapproxy: http://www.imapproxy.org/


PostgreSQL tuning
=================

* Do a ``VACUUM`` command periodically to tune your database.

* Increase ``shared_buffers`` and ``sort_mem`` memory settings.

* If web server and database is on the same unix host, use unix sockets
  instead of network connections for database access.


MySQL tuning
============

* If web server and database is on the same unix host, use unix sockets
  instead of network connections for database access.

* Enable mysql query cache if you have sufficient RAM.  Edit your ``my.cnf``
  file and add the following to the ``[mysqld]`` section (change the memory
  size to meet your needs)::

    set-variable = query_cache_size=128M


Horde tuning
============

Autoloading
-----------

* Horde Groupware Webmail Edition automatically loads PHP source files on
  demand which relies on the PHP autoloading feature introduced with PHP 5 and
  the Horde Autoloader library.  Both allow to limit the set of source code
  files pulled into the system to the minimal amount required to answer the
  current request. This saves memory and time but at the same time the
  Autoloader library has to map each class name to the path of the
  corresponding PHP file that holds the class definition. This procedure is
  expensive and can slow the system down.  Fortunately the mapping is fixed
  unless files are added or removed which usually only happens during an
  upgrade.

  Thus Autoloading is amenable to caching and an easy way to improve the
  performance of the Horde Autoloader library, is to install the Autoloader
  Cache extension::

    pear install horde/horde_autoloader_cache

  This library is not installed by default because it will unconditionally use
  any of the following cache backends and does not allow for any further
  configuration: `Alternative PHP Cache`_, XCache_, eAccelerator_, or the local
  temporary filesystem.

  It also doesn't detect the rare case when the file paths of any PHP class in
  Horde changes. In this case you either need to use the provided script to
  empty the cache::

     horde-autoloader-cache-prune

  or empty the cache manually, e.g. by restarting the web server or deleting
  the cache file from the temporary directory.

VFS
---

* Configure Horde Groupware Webmail Edition to use a VFS filesystem-based
  backend. Presently, the SQL VFS backend uses ~5 times the amount of memory as
  a filesystem-based backend, so users attaching larger files to outgoing mail
  messages may cause PHP out-of-memory errors to occur.


Application tuning
==================

* Some applications contain advanced features that might have a certain impact
  on the performance.  These features can usually be turned off in the
  application's configuration and are explicitly described as being a
  performance hit in the configuration web frontend.


Webmail tuning
==============

* Horde Groupware Webmail Edition can use persistent caching on the server side
  to store information about user's messages.  This results in much reduced
  mail server traffic and requires the server to parse the structure of every
  message only once.  The tradeoff is your cache backend must be able to handle
  the potentially large amounts of cached data this option will
  produce. However, cache storage is potentially cheap when compared to the
  performance gained by using caching.

  If CONDSTORE/QRESYNC is available on the server, IMAP flags can be cached.

  To use this caching, you must have a ``Cache System`` configured in Horde
  Groupware Webmail Edition's ``Administration/Configuration`` screen and have
  the relevant settings enabled in the Mail module's configuration screen
  (``Administration/Configuration/Mail/Mailbox``).
