IMP Performance Guide

Tips on performance tuning systems for IMP. See horde/docs/PERFORMANCE for general performance tips for Horde.

• Use an IMAP server that supports CONDSTORE and/or QRESYNC (RFC 7162).

  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, IMP 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

• IMP 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's Administration/Configuration screen and have the relevant settings enabled in IMP's configuration screen (Administration/Configuration/Mail/Mailbox).

• Consider an IMAP proxy to allow persistent connections.

  imapproxy has been verified to work with IMP. Versions 1.2.7rc1 and greater contains features used internally by Horde to speed up access to the remote server.

  NOTE: if your installation connects to multiple imapproxy instances, you MUST configure your IMP 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.

• Configure Horde 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.