Merge "Updated Weighting section"
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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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