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Phorum 5 performance notes
==========================

Several of Phorum's options have a tradeoff effect: enabling more 
features can slow Phorum down. This document describes which options 
these are and tries to explain the performance cost of each one.

Which options you should turn off to improve performance depends 
on the way you use your Phorum installation.

Table of contents:

1. Global Settings
   1.1 DNS Lookups
   1.2 Count New Private Messages
   1.3 Enable Moderator Notifications
   1.4 Track User Usage
2. Forum Settings
   2.1 Email Messages to Moderators
   2.2 Allow Email Notification
   2.3 Count Views
   2.4 Show New Count in Forum List
   2.5 Ban List
   2.6 Censor List
   2.7 Move Threads on Reply
   2.8 Check for duplicates


1. Global Settings
-------------------------------------------------------------------------------


 1.1 DNS Lookups
 ---------------

    DNS lookups cause Phorum to display DNS entries (hostnames) instead
    of IP addresses on posts. It also will enable checking if mail
    addresses point to valid domains.

    On a forum with a lot of posts, enabling this will result in a
    significant number of queries to your DNS server. Phorum's performance
    will slow down while a query is running, as it will wait for the result
    of the query.

    If your DNS server is slow, this may give the impression to your users
    that posting a message is very slow. If that is the case, you should
    turn DNS lookups off. If you have access to a fast DNS server or only
    have a few regular posters, you should be able to leave it on.


 1.2 Count New Private Messages
 ------------------------------

    If enabled, this option will alert users when they have new private
    messages. On every page a logged in user visits, Phorum will check
    to see if they have new private messages.

    If you have a large number of active users at one time with a large
    number of private messages, this query can start to slow down your
    database. Turning it off may help performance, but will also remove
    the notification users get when they receive a new private message.
    You can also enable userdata caching under "Cache Settings" to
    improve performance.


 1.3 Enable Moderator Notifications
 ----------------------------------

    Similar to the Count New Private Messages option, this option will
    alert users who are also moderators when they have a new item that
    requires their attention.

    The performance hit of this feature is basically nothing for users
    without moderator permissions, as Phorum will never perform the checks.
    Moderators will suffer a small performance hit, depending on what type
    of moderator they are.

    Administrators will suffer a larger performance hit, as they are
    effectively moderators of every type, so all of the checks will be
    performed.


 1.4 Track User Usage
 --------------------

    This option controls how often Phorum will record when a user was last
    active. Setting this to be more frequent results in more accurate last
    activity data, but also causes more database writes.

    The "Constantly" setting will record the users activity on every page
    hit by any logged in user, resulting in a dramatic increase in the number
    of database writes. In most databases, a write is much slower then a
    read, so this can dramatically reduce performance. This setting is not
    recommended, except for installations with very few users, or very
    powerful hardware.

    If you are using a module that actively requires this data (such as the
    Online Users module), the setting "Once per 5 minutes" is the best
    setting, as the data will be too out of date if you update the data
    less frequently.

    If you are not using such a module, "Once per day" or "Once per hour" are
    highly recommended over the other options. "Never" disables this function
    entirely, and is recommended if you simply don't care to know if a user
    is active or not.

    Note: the option "Cache User Data" should be disabled if you have this
    feature set to "Once per 5 minutes" or "Constantly", as the caching
    will not be of much use.


2. Forum Settings
-------------------------------------------------------------------------------


 2.1 Email Messages to Moderators
 --------------------------------

    If enabled, every post in the forum will be emailed to the forum's
    moderators. Administrators are automatically moderators in every forum,
    and will also get the emails.

    This option should not directly affect Phorum's performance, but when
    a post is made, it will cause some emails to be created. If you have a
    large number of moderators and a lot of posts being made by users, this
    can generate a significant amount of email traffic.

    The traffic should only be a problem on very large forums or if you have
    a slow mail server. In other cases, it should not cause significant
    performance issues.


 2.2 Allow Email Notification
 ----------------------------

    This option has similar issues to the Email Messages to Moderators 
    setting, except the recipients of the emails are users who have
    selected the option to have replies in a followed thread emailed to
    them.

    If a large number of users is using this feature in a busy thread, it
    can affect performance. If only few users are using this feature, it 
    will not cause significant performance issues.


 2.3 Count Views
 ---------------
    
    If enabled, this feature records the number of views each post gets.
    For every post read, the counter will be incremented in the database.
    On a busy forum, this will result in a tremendous number of database
    writes, dramatically slowing down performance.

    Enabling this feature is not recommended for high traffic forums,
    unless you have very powerful hardware.


 2.4 Show New Count in Forum List
 --------------------------------

    If enabled, the count of new messages for each forum will appear in
    index.php. While quite handy, this has to run several queries per
    listed forum. If there are many forums on the index.php page, there
    could be a significant performance hit.  

        
 2.5 Ban List
 ------------

    The ban list is a list of words that are banned when posting a message.
    There is a small performance penalty for searching for the banned words,
    but only when posting.


 2.6 Censor List
 ---------------

    The censor list is a list of filtered words, that is checked on every
    post read. Because it is checked far more often than the ban list, a
    large censor list will affect performance much more.


 2.7 Move Threads on Reply
 -------------------------

    "Move Threads on Reply" means that a thread which gets a new reply causes
    the topic to be moved to the top of the forum, hence the topics are
    sorted by their last reply and not by their first post in the message
    list.

    In Flat-mode there is no performance hit. In Threaded-mode it causes
    a large overhead because of the complexity of the sorting and the
    counting of posts on a page.


 2.8 Check for duplicates
 ------------------------
   
    "Check for duplicates" runs one additional query while posting to check
    if that post has been made before. That query should be fast and just
    a small overhead.