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Message retention policies exist at a room level, +follow the semantics described in +<a href="https://github.com/matrix-org/matrix-doc/blob/matthew/msc1763/proposals/1763-configurable-retention-periods.md">MSC1763</a>, +and allow server and room admins to configure how long messages should +be kept in a homeserver's database before being purged from it. +<strong>Please note that, as this feature isn't part of the Matrix +specification yet, this implementation is to be considered as +experimental.</strong></p> +<p>A message retention policy is mainly defined by its <code>max_lifetime</code> +parameter, which defines how long a message can be kept around after +it was sent to the room. If a room doesn't have a message retention +policy, and there's no default one for a given server, then no message +sent in that room is ever purged on that server.</p> +<p>MSC1763 also specifies semantics for a <code>min_lifetime</code> parameter which +defines the amount of time after which an event <em>can</em> get purged (after +it was sent to the room), but Synapse doesn't currently support it +beyond registering it.</p> +<p>Both <code>max_lifetime</code> and <code>min_lifetime</code> are optional parameters.</p> +<p>Note that message retention policies don't apply to state events.</p> +<p>Once an event reaches its expiry date (defined as the time it was sent +plus the value for <code>max_lifetime</code> in the room), two things happen:</p> +<ul> +<li>Synapse stops serving the event to clients via any endpoint.</li> +<li>The message gets picked up by the next purge job (see the "Purge jobs" +section) and is removed from Synapse's database.</li> +</ul> +<p>Since purge jobs don't run continuously, this means that an event might +stay in a server's database for longer than the value for <code>max_lifetime</code> +in the room would allow, though hidden from clients.</p> +<p>Similarly, if a server (with support for message retention policies +enabled) receives from another server an event that should have been +purged according to its room's policy, then the receiving server will +process and store that event until it's picked up by the next purge job, +though it will always hide it from clients.</p> +<p>Synapse requires at least one message in each room, so it will never +delete the last message in a room. It will, however, hide it from +clients.</p> +<h2 id="server-configuration"><a class="header" href="#server-configuration">Server configuration</a></h2> +<p>Support for this feature can be enabled and configured by adding a the +<code>retention</code> in the Synapse configuration file (see +<a href="usage/configuration/config_documentation.html#retention">configuration manual</a>).</p> +<p>To enable support for message retention policies, set the setting +<code>enabled</code> in this section to <code>true</code>.</p> +<h3 id="default-policy"><a class="header" href="#default-policy">Default policy</a></h3> +<p>A default message retention policy is a policy defined in Synapse's +configuration that is used by Synapse for every room that doesn't have a +message retention policy configured in its state. This allows server +admins to ensure that messages are never kept indefinitely in a server's +database. </p> +<p>A default policy can be defined as such, by adding the <code>retention</code> option in +the configuration file and adding these sub-options:</p> +<pre><code class="language-yaml">default_policy: + min_lifetime: 1d + max_lifetime: 1y +</code></pre> +<p>Here, <code>min_lifetime</code> and <code>max_lifetime</code> have the same meaning and level +of support as previously described. They can be expressed either as a +duration (using the units <code>s</code> (seconds), <code>m</code> (minutes), <code>h</code> (hours), +<code>d</code> (days), <code>w</code> (weeks) and <code>y</code> (years)) or as a number of milliseconds.</p> +<h3 id="purge-jobs"><a class="header" href="#purge-jobs">Purge jobs</a></h3> +<p>Purge jobs are the jobs that Synapse runs in the background to purge +expired events from the database. They are only run if support for +message retention policies is enabled in the server's configuration. If +no configuration for purge jobs is configured by the server admin, +Synapse will use a default configuration, which is described here in the +<a href="usage/configuration/config_documentation.html#retention">configuration manual</a>.</p> +<p>Some server admins might want a finer control on when events are removed +depending on an event's room's policy. This can be done by setting the +<code>purge_jobs</code> sub-section in the <code>retention</code> section of the configuration +file. An example of such configuration could be:</p> +<pre><code class="language-yaml">purge_jobs: + - longest_max_lifetime: 3d + interval: 12h + - shortest_max_lifetime: 3d + longest_max_lifetime: 1w + interval: 1d + - shortest_max_lifetime: 1w + interval: 2d +</code></pre> +<p>In this example, we define three jobs:</p> +<ul> +<li>one that runs twice a day (every 12 hours) and purges events in rooms +which policy's <code>max_lifetime</code> is lower or equal to 3 days.</li> +<li>one that runs once a day and purges events in rooms which policy's +<code>max_lifetime</code> is between 3 days and a week.</li> +<li>one that runs once every 2 days and purges events in rooms which +policy's <code>max_lifetime</code> is greater than a week.</li> +</ul> +<p>Note that this example is tailored to show different configurations and +features slightly more jobs than it's probably necessary (in practice, a +server admin would probably consider it better to replace the two last +jobs with one that runs once a day and handles rooms which +policy's <code>max_lifetime</code> is greater than 3 days).</p> +<p>Keep in mind, when configuring these jobs, that a purge job can become +quite heavy on the server if it targets many rooms, therefore prefer +having jobs with a low interval that target a limited set of rooms. Also +make sure to include a job with no minimum and one with no maximum to +make sure your configuration handles every policy.</p> +<p>As previously mentioned in this documentation, while a purge job that +runs e.g. every day means that an expired event might stay in the +database for up to a day after its expiry, Synapse hides expired events +from clients as soon as they expire, so the event is not visible to +local users between its expiry date and the moment it gets purged from +the server's database.</p> +<h3 id="lifetime-limits"><a class="header" href="#lifetime-limits">Lifetime limits</a></h3> +<p>Server admins can set limits on the values of <code>max_lifetime</code> to use when +purging old events in a room. These limits can be defined under the +<code>retention</code> option in the configuration file:</p> +<pre><code class="language-yaml">allowed_lifetime_min: 1d +allowed_lifetime_max: 1y +</code></pre> +<p>The limits are considered when running purge jobs. If necessary, the +effective value of <code>max_lifetime</code> will be brought between +<code>allowed_lifetime_min</code> and <code>allowed_lifetime_max</code> (inclusive). +This means that, if the value of <code>max_lifetime</code> defined in the room's state +is lower than <code>allowed_lifetime_min</code>, the value of <code>allowed_lifetime_min</code> +will be used instead. Likewise, if the value of <code>max_lifetime</code> is higher +than <code>allowed_lifetime_max</code>, the value of <code>allowed_lifetime_max</code> will be +used instead.</p> +<p>In the example above, we ensure Synapse never deletes events that are less +than one day old, and that it always deletes events that are over a year +old.</p> +<p>If a default policy is set, and its <code>max_lifetime</code> value is lower than +<code>allowed_lifetime_min</code> or higher than <code>allowed_lifetime_max</code>, the same +process applies.</p> +<p>Both parameters are optional; if one is omitted Synapse won't use it to +adjust the effective value of <code>max_lifetime</code>.</p> +<p>Like other settings in this section, these parameters can be expressed +either as a duration or as a number of milliseconds.</p> +<h2 id="room-configuration"><a class="header" href="#room-configuration">Room configuration</a></h2> +<p>To configure a room's message retention policy, a room's admin or +moderator needs to send a state event in that room with the type +<code>m.room.retention</code> and the following content:</p> +<pre><code class="language-json">{ + "max_lifetime": ... +} +</code></pre> +<p>In this event's content, the <code>max_lifetime</code> parameter has the same +meaning as previously described, and needs to be expressed in +milliseconds. The event's content can also include a <code>min_lifetime</code> +parameter, which has the same meaning and limited support as previously +described.</p> +<p>Note that over every server in the room, only the ones with support for +message retention policies will actually remove expired events. This +support is currently not enabled by default in Synapse.</p> +<h2 id="note-on-reclaiming-disk-space"><a class="header" href="#note-on-reclaiming-disk-space">Note on reclaiming disk space</a></h2> +<p>While purge jobs actually delete data from the database, the disk space +used by the database might not decrease immediately on the database's +host. However, even though the database engine won't free up the disk +space, it will start writing new data into where the purged data was.</p> +<p>If you want to reclaim the freed disk space anyway and return it to the +operating system, the server admin needs to run <code>VACUUM FULL;</code> (or +<code>VACUUM;</code> for SQLite databases) on Synapse's database (see the related +<a href="https://www.postgresql.org/docs/current/sql-vacuum.html">PostgreSQL documentation</a>).</p> + + </main> + + <nav class="nav-wrapper" aria-label="Page navigation"> + <!-- Mobile navigation buttons --> + <a rel="prev" href="user_directory.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> + <i class="fa fa-angle-left"></i> + </a> + <a rel="next" href="modules/index.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> + <i class="fa fa-angle-right"></i> + </a> + <div style="clear: both"></div> + </nav> + </div> + </div> + + <nav class="nav-wide-wrapper" aria-label="Page navigation"> + <a rel="prev" href="user_directory.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> + <i class="fa fa-angle-left"></i> + </a> + <a rel="next" href="modules/index.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> + <i class="fa fa-angle-right"></i> + </a> + </nav> + + </div> + + <script type="text/javascript"> + window.playground_copyable = true; + </script> + <script src="elasticlunr.min.js" type="text/javascript" charset="utf-8"></script> + <script src="mark.min.js" type="text/javascript" charset="utf-8"></script> + <script src="searcher.js" type="text/javascript" charset="utf-8"></script> + <script src="clipboard.min.js" type="text/javascript" charset="utf-8"></script> + <script src="highlight.js" type="text/javascript" charset="utf-8"></script> + <script src="book.js" type="text/javascript" charset="utf-8"></script> + + <!-- Custom JS scripts --> + <script type="text/javascript" src="docs/website_files/table-of-contents.js"></script> + <script type="text/javascript" src="docs/website_files/version-picker.js"></script> + <script type="text/javascript" src="docs/website_files/version.js"></script> + </body> +</html> |