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<section id="mailbox-creation-distribution">
<h1>Mailbox Creation Distribution<a class="headerlink" href="#mailbox-creation-distribution" title="Permalink to this heading"></a></h1>
<p>By default, when creating a mailbox in Cyrus IMAP:</p>
<ul class="simple">
<li><p>the backend with the most free disk space is selected on the Murder frontend</p></li>
<li><p>the partition with the most free disk space is selected on the backend</p></li>
</ul>
<p>This may not be the most appropriate backend or partition to create the new mailbox on, and Cyrus IMAP therefor allows for a variety of additional modes of calculating and selecting the most appropriate backend and partition. The exact mode for the selection is controlled with the <code class="docutils literal notranslate"><span class="pre">imapd.conf</span></code> setting <code class="docutils literal notranslate"><span class="pre">serverlist_select_mode</span></code> on the frontend and <code class="docutils literal notranslate"><span class="pre">partition_select_mode</span></code> on the backend.</p>
<p>Alternatively, a default backend can be configured with the <code class="docutils literal notranslate"><span class="pre">defaultserver</span></code> setting on a frontend, and a default partition can be configured with the <code class="docutils literal notranslate"><span class="pre">defaultpartition</span></code> on a backend.</p>
<p>Prior to Cyrus IMAP version 2.5, when creating a mailbox, should no
target partition have been specified, the mailbox is either created on:</p>
<ul class="simple">
<li><p>the configured <code class="docutils literal notranslate"><span class="pre">defaultserver</span></code>, or</p></li>
<li><p>the server that is found to have the most free disk space, and</p></li>
<li><p>the configured <code class="docutils literal notranslate"><span class="pre">defaultpartition</span></code>, or</p></li>
<li><p>the most fitting partition if <code class="docutils literal notranslate"><span class="pre">defaultpartition</span></code> is not
configured.</p></li>
</ul>
<p>New configuration options are available since Cyrus IMAP 2.5, that
allow more weighted and better balanced backend and partition
selection.</p>
<section id="selection-mode">
<h2>Selection Mode<a class="headerlink" href="#selection-mode" title="Permalink to this heading"></a></h2>
<p>Among the partitions, how the most fitting one is selected depends on the configured selection mode: <code class="docutils literal notranslate"><span class="pre">partition_mode</span></code> setting in <code class="docutils literal notranslate"><span class="pre">/etc/imapd.conf</span></code></p>
<section id="available-selection-modes">
<h3>Available Selection Modes<a class="headerlink" href="#available-selection-modes" title="Permalink to this heading"></a></h3>
<ul>
<li><p>random</p>
<blockquote>
<div><p>Choice is (pseudo-)random. Each partition has the same probability of being selected.</p>
</div></blockquote>
</li>
<li><p>freespace-most</p>
<blockquote>
<div><p>The partition which has the most free space (counted in KiB units) is selected.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of <code class="docutils literal notranslate"><span class="pre">freespace-most</span></code> selection on backend</p>
<p>Suppose that the configured partitions are:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">part1</span></code> which has a 1000GiB capacity, 400GiB being free (that is, 40% free space)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part2</span></code> which has a 1000GiB capacity, 600GiB being free (that is, 60% free space)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part3</span></code> which has a 100GiB capacity, 30GiB being free (that is, 30% free space)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part4</span></code> which has a 100GiB capacity, 70GiB being free (that is, 70% free space)</p></li>
</ul>
<p>In that case <code class="docutils literal notranslate"><span class="pre">part2</span></code> will be selected as most fitting, since 600GiB of free space is the biggest of all partitions.</p>
</div>
</div></blockquote>
</li>
<li><p>freespace-percent-most</p>
<blockquote>
<div><p>The partition which has the most percentage of free space is selected.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of <code class="docutils literal notranslate"><span class="pre">freespace-percent-most</span></code> selection on backend</p>
<p>In the same conditions, <code class="docutils literal notranslate"><span class="pre">part4</span></code> would be selected as most fitting, since 70% of free space is the biggest of all partitions.</p>
</div>
</div></blockquote>
</li>
<li><p>freespace-percent-weighted</p>
<blockquote>
<div><p>For each partition, the percentage of free space is its weight. Then a weighted choice is performed to select one of those partitions.</p>
<p>As such, the more free space the partition has, the more chances it has to be selected.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of <code class="docutils literal notranslate"><span class="pre">freespace-percent-weighted</span></code> selection on backend</p>
<p>In the same conditions, the weight of each partition would be:</p>
<ul class="simple">
<li><p>40 for <code class="docutils literal notranslate"><span class="pre">part1</span></code></p></li>
<li><p>60 for <code class="docutils literal notranslate"><span class="pre">part2</span></code></p></li>
<li><p>30 for <code class="docutils literal notranslate"><span class="pre">part3</span></code></p></li>
<li><p>70 for <code class="docutils literal notranslate"><span class="pre">part4</span></code></p></li>
</ul>
<p>The sum of each weight being 200, the probability for each partition to be selected as most fitting would be:</p>
<ul class="simple">
<li><p>20% for <code class="docutils literal notranslate"><span class="pre">part1</span></code></p></li>
<li><p>30% for <code class="docutils literal notranslate"><span class="pre">part2</span></code></p></li>
<li><p>15% for <code class="docutils literal notranslate"><span class="pre">part3</span></code></p></li>
<li><p>35% for <code class="docutils literal notranslate"><span class="pre">part4</span></code></p></li>
</ul>
</div>
</div></blockquote>
</li>
</ul>
</section>
<section id="usage-convergence">
<h3>Usage convergence<a class="headerlink" href="#usage-convergence" title="Permalink to this heading"></a></h3>
<p>In <code class="docutils literal notranslate"><span class="pre">freespace-percent-weighted</span></code> mode, partitions percentage usages converge towards 100%. So if they have different usages, those differences will stay and only really diminish upon reaching 100% of usage.</p>
<p>You may also observe growing differences between partitions usage when those partitions do not have the same total disk space.</p>
<ul class="simple">
<li><p>freespace-percent-weighted-delta</p></li>
</ul>
<p>As for <code class="docutils literal notranslate"><span class="pre">freespace-percent-weighted</span></code>, a weight is associated to each partition. It is computed as follows: (<em>percentage of freespace of partition</em>) - (<em>lowest percentage of freespace of all partitions</em>) + 0.5</p>
<p>Then a weighted choice is performed to select one of those partitions.</p>
<p>As such, considering the percentages of usage, the more the partition is lagging behind the most used partition (which is the one with the lowest percentage of free space), the more chances it has to be selected.</p>
</section>
<section id="computed-weight">
<h3>Computed weight<a class="headerlink" href="#computed-weight" title="Permalink to this heading"></a></h3>
<p>The added 0.5 in partitions weight is so that selection gets smoother when all partitions get close to each other.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p><strong>Example of ``freespace-percent-weighted-delta`` Selection on Backend</strong></p>
<p>In the same conditions, the weight of each partition would be:</p>
<ul class="simple">
<li><p>40 - 30 + 0.5 = 10.5 for <code class="docutils literal notranslate"><span class="pre">part1</span></code></p></li>
<li><p>60 - 30 + 0.5 = 30.5 for <code class="docutils literal notranslate"><span class="pre">part2</span></code></p></li>
<li><p>30 - 30 + 0.5 = 0.5 for <code class="docutils literal notranslate"><span class="pre">part3</span></code></p></li>
<li><p>70 - 30 + 0.5 = 40.5 for <code class="docutils literal notranslate"><span class="pre">part4</span></code></p></li>
</ul>
<p>Then the probability for each partition to be selected as most fitting would be:</p>
<ul class="simple">
<li><p>12.8% for <code class="docutils literal notranslate"><span class="pre">part1</span></code></p></li>
<li><p>37.2% for <code class="docutils literal notranslate"><span class="pre">part2</span></code></p></li>
<li><p>0.6% for <code class="docutils literal notranslate"><span class="pre">part3</span></code></p></li>
<li><p>49.4% for <code class="docutils literal notranslate"><span class="pre">part4</span></code></p></li>
</ul>
<p><strong>Usage convergence</strong></p>
<p>In <code class="docutils literal notranslate"><span class="pre">freespace-percent-weighted-delta</span></code> mode, partitions percentage usages converge towards the most used one. And then partitions usages grow equally.</p>
</div>
</section>
</section>
<section id="special-cases">
<h2>Special cases<a class="headerlink" href="#special-cases" title="Permalink to this heading"></a></h2>
<section id="what-happens-when-two-partitions-are-equal-as-most-fitting">
<h3>What happens when two partitions are equal as most fitting?<a class="headerlink" href="#what-happens-when-two-partitions-are-equal-as-most-fitting" title="Permalink to this heading"></a></h3>
<p>Suppose you are using the <code class="docutils literal notranslate"><span class="pre">freespace-most</span></code> selection mode, that two (or more) partitions have the same free size, and that this freespace happens to be the biggest one of all configured partitions.</p>
<p>In that case, only one of those partitions will be selected. You may not know in advance which one will be: it depends of the order in which configured partitions are stored in memory (<code class="docutils literal notranslate"><span class="pre">hashtable</span></code>). In particular, it may not be the first one that appears listed in your <code class="docutils literal notranslate"><span class="pre">/etc/imapd.conf</span></code> configuration file.</p>
<p>Also note that since the selected partition will now have less free space, it shall not be seen as most fitting next time.</p>
</section>
<section id="what-happens-when-two-partitions-point-to-the-same-device">
<h3>What happens when two partitions point to the same device?<a class="headerlink" href="#what-happens-when-two-partitions-point-to-the-same-device" title="Permalink to this heading"></a></h3>
<p>Suppose you are using the <code class="docutils literal notranslate"><span class="pre">freespace-most</span></code> or <code class="docutils literal notranslate"><span class="pre">freespace-percent-most</span></code> selection mode, and that two (or more) partitions actually point to the same device (that is the device id is the same).</p>
<p>In that case, only one of those partitions will be checked, as if the others were not configured. You may not know in advance which one will be: it depends of the order in which configured partitions are stored in memory (<code class="docutils literal notranslate"><span class="pre">hashtable</span></code>). In particular, it may not be the first one that appears listed in your <code class="docutils literal notranslate"><span class="pre">/etc/imapd.conf</span></code> configuration file.</p>
</section>
</section>
<section id="partitions-exclusion">
<h2>Partitions Exclusion<a class="headerlink" href="#partitions-exclusion" title="Permalink to this heading"></a></h2>
<p>Partitions listed in the <code class="docutils literal notranslate"><span class="pre">partition_mode_exclude</span></code> setting are permanently excluded from being selected.</p>
<ul>
<li><p>partition_mode_exclude</p>
<blockquote>
<div><p>Listed partitions names are separated by space or comma. Only configured partition names (and not paths) are expected.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of permanent partition exclusion</p>
<p>With the following configuration in <cite>/etc/imapd.conf</cite>, <code class="docutils literal notranslate"><span class="pre">parta</span></code> and <code class="docutils literal notranslate"><span class="pre">partb</span></code> would be permanently excluded from being selected:</p>
<p>partition-part1: /path/to/part1
partition-part2: /path/to/part2
partition-part3: /path/to/part3
partition-part4: /path/to/part4
partition-parta: /path/to/parta
partition-partb: /path/to/partb</p>
<p>partition_mode_exclude: parta partb</p>
<p>When using a selection mode other than <code class="docutils literal notranslate"><span class="pre">random</span></code>, partitions are automatically excluded if their usage percentage is beyond the <code class="docutils literal notranslate"><span class="pre">partition_mode_soft_usage_limit</span></code> integer setting.</p>
</div>
</div></blockquote>
</li>
<li><p>partition_mode_soft_usage_limit</p>
<blockquote>
<div><p>If all partitions are beyond the configured value, this feature is automatically deactivated. A partition is thus selected as if the setting was not set.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of partition exclusion using <code class="docutils literal notranslate"><span class="pre">partition_mode_soft_usage_limit</span></code></p>
<p>In the same conditions than <xref linkend="exam-Deployment_Guide-Available_Selection_Modes_on_Backend-Example_of_freespace_most_Selection_on_Backend" />, setting <code class="docutils literal notranslate"><span class="pre">partition_mode_soft_usage_limit</span></code> to <code class="docutils literal notranslate"><span class="pre">50</span></code> would exclude partitions <code class="docutils literal notranslate"><span class="pre">part1</span></code> and <code class="docutils literal notranslate"><span class="pre">part3</span></code> since their disk usage is respectively 60% and 70%.</p>
<p>But setting the option to <code class="docutils literal notranslate"><span class="pre">20</span></code> would have no effect, since the usage of all partitions is beyond 20%.</p>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p><strong>Exclusion is not absolute</strong></p>
<p>Partitions are only excluded when creating a new user mailbox according to the configured selection mode.</p>
<p>If you explicitly specify an excluded partition, the mailbox will be created on that partition.</p>
<p>Mailboxes previously created on such partitions are of course still accessible, and subfolders are by default still created on the same partition as the parent folder.</p>
</div>
</div></blockquote>
</li>
</ul>
</section>
<section id="partitions-usage-data-reset">
<h2>Partitions Usage Data Reset<a class="headerlink" href="#partitions-usage-data-reset" title="Permalink to this heading"></a></h2>
<p>By default partitions usage data are retrieved only once upon service initialization. This only concerns selection modes other than <code class="docutils literal notranslate"><span class="pre">random</span></code>.</p>
<p>If you tend to use the same service instance for a long lapse of time and performs a large amount of mailboxes creation, it may be useful to configure the <code class="docutils literal notranslate"><span class="pre">partition_mode_usage_reinit</span></code> so that partitions usage data are refreshed after the configured number of creation requests.</p>
</section>
<section id="mailbox-creation-distribution-through-murder-frontend">
<h2>Mailbox Creation Distribution Through <code class="docutils literal notranslate"><span class="pre">murder</span> <span class="pre">frontend</span></code><a class="headerlink" href="#mailbox-creation-distribution-through-murder-frontend" title="Permalink to this heading"></a></h2>
<p>Upon creating a user mailbox, if the target server is not given as extra parameter, the mailbox is either created on</p>
<ul class="simple">
<li><p>the configured <code class="docutils literal notranslate"><span class="pre">defaultserver</span></code> backend</p></li>
<li><p>the most fitting backend among the servers listed in the <code class="docutils literal notranslate"><span class="pre">serverlist</span></code> setting, if <code class="docutils literal notranslate"><span class="pre">defaultserver</span></code> is not configured</p></li>
</ul>
<section id="id2">
<h3>Selection Mode<a class="headerlink" href="#id2" title="Permalink to this heading"></a></h3>
<p>Among the backends, how the most fitting one is selected depends on the configured selection mode: <code class="docutils literal notranslate"><span class="pre">serverlist_mode</span></code> setting in <code class="docutils literal notranslate"><span class="pre">/etc/imapd.conf</span></code>.</p>
<p>The principle is similar to the mailbox creation distribution on backend (see <xref linkend="sect-Deployment_Guide-Mailbox_Creation_Distribution-On_backend" />).</p>
</section>
<section id="available-selection-modes-on-frontend">
<h3>Available Selection Modes on Frontend<a class="headerlink" href="#available-selection-modes-on-frontend" title="Permalink to this heading"></a></h3>
<ul>
<li><p>random</p>
<blockquote>
<div><p>Choice is (pseudo-)random. Each backend has the same probability of being selected.</p>
</div></blockquote>
</li>
<li><p>freespace-most</p>
<blockquote>
<div><p>The backend which has the most free space (counted in KiB units) is selected. The considered free space is the sum of all available partitions free space on the backend.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of <code class="docutils literal notranslate"><span class="pre">freespace-most</span></code> Selection on Frontend</p>
<p>Suppose that the configured backends are:</p>
<ul>
<li><p><code class="docutils literal notranslate"><span class="pre">backend1</span></code> which has a 2000GiB capacity, 1000GiB being free (that is, 50% free space), composed of 2 partitions</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part1</span></code> which has a 1000GiB capacity, 500GiB being free (that is, 50% free space)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part2</span></code> which has a 1000GiB capacity, 500GiB being free (that is, 50% free space)</p>
<blockquote>
<div><ul>
<li><p><code class="docutils literal notranslate"><span class="pre">backend2</span></code> which has a 2000GiB capacity, 900GiB being free (that is, 45% free space), composed of 2 partitions</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part1</span></code> which has a 1000GiB capacity, 200GiB being free (that is, 20% free space)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part2</span></code> which has a 1000GiB capacity, 700GiB being free (that is, 70% free space)</p>
<blockquote>
<div><ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">backend3</span></code> which has a 200GiB capacity, 110GiB being free (that is, 55% free space), composed of 2 partitions</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part1</span></code> which has a 100GiB capacity, 30GiB being free (that is, 30% free space)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">part2</span></code> which has a 100GiB capacity, 80GiB being free (that is, 80% free space)</p></li>
</ul>
</div></blockquote>
</li>
</ul>
</div></blockquote>
</li>
<li><p>In that case <code class="docutils literal notranslate"><span class="pre">backend1</span></code> will be selected as most fitting, since 1000GiB of free space is the biggest of all backends.</p></li>
</ul>
</div>
</div></blockquote>
</li>
<li><p>freespace-percent-most</p>
<blockquote>
<div><p>On each backend, the partition with the most percentage of free space is considered. The selected backend is the one whose partition has the most percentage of free space.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of <code class="docutils literal notranslate"><span class="pre">freespace-percent-most</span></code> Selection on Frontend</p>
<p>In the same conditions than <xref linkend="exam-Deployment_Guide-Available_Selection_Modes_on_Frontend-Example_of_freespace_most_Selection_on_Frontend" /> <code class="docutils literal notranslate"><span class="pre">backend3</span></code> would be selected as most fitting, since it has a partition with 80% of free space which is the biggest of all backends.</p>
</div>
</div></blockquote>
</li>
<li><p>freespace-percent-weighted</p>
<blockquote>
<div><p>On each backend, the partition with the most percentage of free space is considered: it is the backend weight. Then a weighted choice is performed to select one of the backends.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of <code class="docutils literal notranslate"><span class="pre">freespace-percent-weighted</span></code> Selection on Frontend</p>
<p>In the same conditions than <xref linkend="exam-Deployment_Guide-Available_Selection_Modes_on_Frontend-Example_of_freespace_most_Selection_on_Frontend" />, the weight of each backend would be:</p>
<blockquote>
<div><ul class="simple">
<li><p>50 for <code class="docutils literal notranslate"><span class="pre">backend1</span></code></p></li>
<li><p>70 for <code class="docutils literal notranslate"><span class="pre">backend2</span></code></p></li>
<li><p>80 for <code class="docutils literal notranslate"><span class="pre">backend3</span></code></p></li>
</ul>
</div></blockquote>
<p>The sum of each weight being 200, the probability for each backend to be selected as most fitting would be:</p>
<blockquote>
<div><ul class="simple">
<li><p>25% for <code class="docutils literal notranslate"><span class="pre">backend1</span></code></p></li>
<li><p>35% for <code class="docutils literal notranslate"><span class="pre">backend2</span></code></p></li>
<li><p>40% for <code class="docutils literal notranslate"><span class="pre">backend3</span></code></p></li>
</ul>
</div></blockquote>
</div>
</div></blockquote>
</li>
<li><p>freespace-percent-weighted-delta</p></li>
</ul>
<p>On each backend, the partition with the most percentage of free space is considered. As for <code class="docutils literal notranslate"><span class="pre">freespace-percent-weighted</span></code>, a weight is associated to each backend. It is computed as follows: (<em>percentage of freespace on backend</em>) - (<em>lowest percentage of freespace of all backends</em>) + 0.5</p>
<p>Then a weighted choice is performed to select one of the backends.</p>
<blockquote>
<div><div class="admonition note">
<p class="admonition-title">Note</p>
<p><strong>Example of ``freespace-percent-weighted-delta`` Selection on Frontend</strong></p>
<p>In the same conditions than <xref linkend="exam-Deployment_Guide-Available_Selection_Modes_on_Frontend-Example_of_freespace_most_Selection_on_Frontend" />, the weight of each backend would be:</p>
<ul class="simple">
<li><p>50 - 50 + 0.5 = 0.5 for <code class="docutils literal notranslate"><span class="pre">backend1</span></code></p></li>
<li><p>70 - 50 + 0.5 = 20.5 for <code class="docutils literal notranslate"><span class="pre">backend2</span></code></p></li>
<li><p>80 - 50 + 0.5 = 30.5 for <code class="docutils literal notranslate"><span class="pre">backend3</span></code></p></li>
</ul>
<p>Then the probability for each backend to be selected as most fitting would be:</p>
<ul class="simple">
<li><p>1.0% for <code class="docutils literal notranslate"><span class="pre">backend1</span></code></p></li>
<li><p>39.8% for <code class="docutils literal notranslate"><span class="pre">backend2</span></code></p></li>
<li><p>59.2% for <code class="docutils literal notranslate"><span class="pre">backend3</span></code></p></li>
</ul>
</div>
</div></blockquote>
</section>
</section>
<section id="backends-exclusion">
<h2>Backends Exclusion<a class="headerlink" href="#backends-exclusion" title="Permalink to this heading"></a></h2>
<p>When using a selection mode other than <code class="docutils literal notranslate"><span class="pre">random</span></code>, backends are automatically excluded if their considered usage percentage is beyond the <code class="docutils literal notranslate"><span class="pre">serverlist_mode_soft_usage_limit</span></code> integer setting.</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">partition_mode_soft_usage_limit</span></code></p></li>
</ul>
<p>If all backends are beyond the configured value, this feature is automatically deactivated. A backend is thus selected as if the setting was not set.</p>
<blockquote>
<div><div class="admonition note">
<p class="admonition-title">Note</p>
<p>Example of partition exclusion using <code class="docutils literal notranslate"><span class="pre">serverlist_mode_soft_usage_limit</span></code></p>
<p>In the same conditions than <xref linkend="exam-Deployment_Guide-Available_Selection_Modes_on_Frontend-Example_of_freespace_most_Selection_on_Frontend" />, using <code class="docutils literal notranslate"><span class="pre">freespace-most</span></code> selection mode, setting <code class="docutils literal notranslate"><span class="pre">serverlist_mode_soft_usage_limit</span></code> to <code class="docutils literal notranslate"><span class="pre">49</span></code> would exclude <code class="docutils literal notranslate"><span class="pre">backend1</span></code> and <code class="docutils literal notranslate"><span class="pre">backend2</span></code> since in that mode they have a disk usage of 50% and 55%. In other modes it would however only exclude <code class="docutils literal notranslate"><span class="pre">backend1</span></code> whose considered partition has a disk usage of 50%, while on <code class="docutils literal notranslate"><span class="pre">backend2</span></code> the considered partition has a disk usage of 30%.</p>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p><strong>Exclusion is not absolute</strong></p>
<p>Backends are only excluded when creating a new user mailbox according to the configured selection mode.</p>
<p>If you explicitly specify an excluded backend, the mailbox will be created on that backend.</p>
<p>Mailboxes previously created on such backends are of course still accessible.</p>
</div>
</div></blockquote>
</section>
<section id="backends-usage-data-reset">
<h2>Backends Usage Data Reset<a class="headerlink" href="#backends-usage-data-reset" title="Permalink to this heading"></a></h2>
<p>By default backends usage data are retrieved only once upon service initialization. This only concerns selection modes other than <code class="docutils literal notranslate"><span class="pre">random</span></code>.</p>
<p>If you tend to use the same service instance for a long lapse of time and performs a large amount of mailboxes creation, it may be useful to configure the <code class="docutils literal notranslate"><span class="pre">serverlist_mode_usage_reinit</span></code> so that backends usage data are refreshed after the configured number of creation requests.</p>
</section>
</section>
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