virt plugin: Document Instances option

Documented implementation from 452324c4a5b6ec07575cfc5d5d339852b040509b

diff --git a/src/collectd.conf.pod b/src/collectd.conf.pod
index 03b163e..2f3322f 100644 (file)
--- a/src/collectd.conf.pod
+++ b/src/collectd.conf.pod
@@ -9330,12 +9330,6 @@ You can also specify combinations of the B<name> and B<uuid> fields.
 For example B<name uuid> means to concatenate the guest name and UUID
 (with a literal colon character between, thus I<"foo:1234-1234-1234-1234">).
 
 For example B<name uuid> means to concatenate the guest name and UUID
 (with a literal colon character between, thus I<"foo:1234-1234-1234-1234">).
 

-=item B<Instances> B<integer>
-
-How many read instances you want to use for this plugin. The default is one,
-and the sensible setting is a multiple of the B<ReadThreads> value.
-If you are not sure, just use the default setting.
-

 =item B<ExtraStats> B<string>
 
 Report additional extra statistics. The default is no extra statistics, preserving
 =item B<ExtraStats> B<string>
 
 Report additional extra statistics. The default is no extra statistics, preserving


@@ -9386,11 +9380,38 @@ B<Note>: I<perf> metrics can't be collected if I<intel_rdt> plugin is enabled.
 =back
 
 =item B<PersistentNotification> B<true>|B<false>
 =back
 
 =item B<PersistentNotification> B<true>|B<false>

+

 Override default configuration to only send notifications when there is a change
 in the lifecycle state of a domain. When set to true notifications will be sent
 for every read cycle. Default is false. Does not affect the stats being
 dispatched.
 
 Override default configuration to only send notifications when there is a change
 in the lifecycle state of a domain. When set to true notifications will be sent
 for every read cycle. Default is false. Does not affect the stats being
 dispatched.
 

+=item B<Instances> B<integer>
+
+How many read instances you want to use for this plugin. The default is one,
+and the sensible setting is a multiple of the B<ReadThreads> value.
+
+This option is only useful then domains are specially tagged.
+If you are not sure, just use the default setting.
+
+The reader instance will only query the domains with attached a matching tag.
+Tags should have the form of 'virt-X' where X is reader instance number,
+starting from 0.
+
+The special-purpose reader instance #0, guaranteed to be always present,
+will query all the domains with missing or unrecognized tag, so no domain will
+ever left out.
+
+Domain tagging is done with custom attribute in the libvirt domain metadata
+section. Value is taken by XPath I</domain/metadata/ovirtmap/tag/text()>
+expression in I<http://ovirt.org/ovirtmap/tag/1.0> namespace.
+(XPath and namespace values are not configurable yet).
+
+Tagging could be used by management application to evenly spread the
+load among the reader threads, or to pin on the same threads all
+the libvirt domains which use the same shared storage, to minimize
+the disruption in presence of storage outages.
+

 =back
 
 =head2 Plugin C<vmem>
 =back
 
 =head2 Plugin C<vmem>