Updated Weighting section
Put in tables of relevant weighting options for both hosts and cells. Updated intro. Added graphic from training guides (moved into common and relinked in training guide). Closes-bug: #1261521 Change-Id: Ic9fd323e31016040dbbf18be4969ff829d4edf1e
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<!DOCTYPE section [
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<!-- Some useful entities borrowed from HTML -->
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<!ENTITY nbsp " ">
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<!ENTITY mdash "—">
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]>
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<section xml:id="section_compute-scheduler"
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xmlns="http://docbook.org/ns/docbook"
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@ -490,19 +491,159 @@ isolated_images=342b492c-128f-4a42-8d3a-c5088cf27d13,ebd267a6-ca86-4d6c-9a0e-bd1
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<section xml:id="weights">
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<title>Weights</title>
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<?dbhtml stop-chunking?>
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<para>The Filter Scheduler weighs hosts based on the config
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option <literal>scheduler_weight_classes</literal>, this
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defaults to
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<literal>nova.scheduler.weights.all_weighers</literal>,
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which selects the only weigher available -- the
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RamWeigher. Hosts are then weighed and sorted with the
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largest weight winning.</para>
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<programlisting language="ini">scheduler_weight_classes=nova.scheduler.weights.all_weighers
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ram_weight_multiplier=1.0</programlisting>
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<para>The default is to spread instances across all hosts
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evenly. Set the <literal>ram_weight_multiplier</literal>
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option to a negative number if you prefer stacking instead
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of spreading.</para>
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<para>When resourcing instances, the Filter Scheduler filters and weighs each host in the
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list of acceptable hosts. Each time the scheduler selects a host, it virtually consumes
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resources on it, and subsequent selections are adjusted accordingly. This process is
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useful when the customer asks for the same large amount of instances, because weight is
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computed for each requested instance.</para>
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<para>All weights are normalized before being summed up; the host with the largest weight is
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given the highest priority.</para>
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<figure xml:id="figure_weighing-hosts">
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<title>Weighing hosts</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="../../common/figures/nova-weighting-hosts.png"/>
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</imageobject>
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</mediaobject>
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</figure>
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<para>If cells are used, cells are weighted by the scheduler in the same manner as hosts.</para>
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<para>Hosts and cells are weighed based on the following options in the
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<filename>/etc/nova/nova.conf</filename> file:</para>
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<table rules="all" xml:id="table_host-weighting-options">
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<caption>Host Weighting options</caption>
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<col width="10%" title="Section"/>
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<col width="25%" title="Option"/>
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<col width="60%" title="Description"/>
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<thead>
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<tr>
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<th>Section</th>
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<th>Option</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr valign="top">
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<td>[DEFAULT]</td>
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<td><literal>ram_weight_multiplier</literal></td>
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<td>By default, the scheduler spreads instances across all hosts evenly. Set the
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<option>ram_weight_multiplier</option> option to
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a negative number if you prefer stacking instead of spreading. Use a
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floating-point value.</td>
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</tr>
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<tr valign="top">
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<td>[DEFAULT]</td>
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<td><literal>scheduler_host_subset_size</literal></td>
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<td>New instances are scheduled on a host that is chosen randomly from a subset
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of the N best hosts. This property defines the subset size from which a host
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is chosen. A value of 1 chooses the first host returned by the weighing
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functions.This value must be at least 1. A value less than 1 is ignored, and
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1 is used instead. Use an integer value.</td>
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</tr>
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<tr valign="top">
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<td>[DEFAULT]</td>
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<td><literal>scheduler_weight_classes</literal></td>
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<td>Defaults to <literal>nova.scheduler.weights.all_weighers</literal>, which
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selects the only available weigher, the RamWeigher. Hosts are then weighed
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and sorted with the largest weight winning.</td>
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</tr>
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<tr valign="top">
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<td>[metrics]</td>
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<td><literal>weight_multiplier</literal></td>
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<td>Multiplier for weighing metrices. Use a floating-point value.</td>
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</tr>
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<tr valign="top">
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<td>[metrics]</td>
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<td><literal>weight_setting</literal></td>
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<td>Determines how metrics are weighed. Use a comma-separated list of
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metricName=ratio. For example: "name1=1.0, name2=-1.0" results in:
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<literal>name1.value * 1.0 + name2.value * -1.0</literal>
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</td>
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</tr>
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<tr valign="top">
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<td>[metrics]</td>
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<td><literal>required</literal></td>
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<td><para>Specifies how to treat unavailable metrics:<itemizedlist>
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<listitem><para>True—Raises an exception. To avoid the raised exception, you should use the scheduler
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filter <literal>MetricFilter</literal> to filter out hosts
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with unavailable metrics.</para></listitem>
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<listitem><para>False—Treated as a negative factor in the weighing process (uses the
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<option>weight_of_unavailable</option> option).</para></listitem>
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</itemizedlist></para></td>
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</tr>
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<tr valign="top">
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<td>[metrics]</td>
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<td><literal>weight_of_unavailable</literal></td>
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<td>If <option>required</option> is set to False, and any one of the metrics set
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by <option>weight_setting</option> is unavailable, the
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<option>weight_of_unavailable</option> value is returned to the
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scheduler.</td>
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</tr>
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</tbody>
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</table>
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<para>For example:</para>
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<programlisting language="ini">[DEFAULT]
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scheduler_host_subset_size=1
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scheduler_weight_classes=nova.scheduler.weights.all_weighers
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ram_weight_multiplier=1.0
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[metrics]
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weight_multiplier=1.0
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weight_setting=name1=1.0, name2=-1.0
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required=false
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weight_of_unavailable=-10000.0</programlisting>
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<table rules="all" xml:id="table_cell-weighting-options">
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<caption>Cell weighting options</caption>
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<col width="10%" title="Section"/>
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<col width="25%" title="Option"/>
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<col width="60%" title="Description"/>
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<thead>
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<tr>
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<th>Section</th>
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<th>Option</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr valign="top">
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<td>[cells]</td>
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<td><literal>mute_weight_multiplier</literal></td>
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<td>Multiplier to weigh mute children (hosts which have not sent capacity or
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capacity updates for some time). Use a negative, floating-point value.</td>
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</tr>
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<tr valign="top">
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<td>[cells]</td>
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<td><literal>mute_weight_value</literal></td>
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<td>Weight value assigned to mute children. Use a positive, floating-point value
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with a maximum of '1.0'.</td>
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</tr>
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<tr valign="top">
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<td>[cells]</td>
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<td><literal>offset_weight_multiplier</literal></td>
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<td>Multiplier to weigh cells, so you can specify a preferred cell. Use a floating
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point value.</td>
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</tr>
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<tr valign="top">
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<td>[cells]</td>
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<td><literal>ram_weight_multiplier</literal></td>
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<td>By default, the scheduler spreads instances across all cells evenly. Set the
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<option>ram_weight_multiplier</option> option to a negative number if
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you prefer stacking instead of spreading. Use a floating-point value.</td>
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</tr>
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<tr valign="top">
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<td>[cells]</td>
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<td><literal>scheduler_weight_classes</literal></td>
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<td>Defaults to <literal>nova.cells.weights.all_weighers</literal>, which maps to
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all cell weighers included with Compute. Cells are then weighed and sorted
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with the largest weight winning.</td>
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</tr>
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</tbody>
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</table>
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<para>For example:</para>
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<programlisting language="ini">[cells]
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scheduler_weight_classes=nova.cells.weights.all_weighers
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mute_weight_multiplier=-10.0
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mute_weight_value=1000.0
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ram_weight_multiplier=1.0
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offset_weight_multiplier=1.0</programlisting>
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</section>
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<section xml:id="chance-scheduler">
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<title>Chance scheduler</title>
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@ -196,7 +196,7 @@
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<title>Weights</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="figures/image07.png"/>
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<imagedata fileref="../common/figures/nova-weighting-hosts.png"/>
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</imageobject>
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</mediaobject>
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</figure>
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