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doc: document "child_node" events
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Ian Barwick
@@ -165,7 +165,7 @@
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</sect1>
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<sect1 id="repmgrd-primary-standby-disconnection" xreflabel="Monitoring standby disconnections on the primary">
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<sect1 id="repmgrd-primary-child-disconnection" xreflabel="Monitoring standby disconnections on the primary">
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<indexterm>
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<primary>repmgrd</primary>
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<secondary>standby disconnection</secondary>
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@@ -192,13 +192,19 @@
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example to "fence" the node and ensure it is isolated from any
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applications attempting to access the replication cluster.
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</para>
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<para>
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<sect2 id="repmgrd-primary-child-disconnection-monitoring-process">
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<title>Standby disconnections monitoring process and criteria</title>
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<para>
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<application>repmgrd</application> monitors attach child nodes and decides
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whether to invoke the user-defined command based on the following process
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and criteria:
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<itemizedlist>
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<listitem>
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<para>
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Every few seconds (defined by the configuration parameter <varname>child_nodes_check_interval</varname>
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(a value of <literal>0</literal> disables this altogether), <application>repmgrd</application> queries
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Every few seconds (defined by the configuration parameter <varname>child_nodes_check_interval</varname>;
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a value of <literal>0</literal> disables this altogether), <application>repmgrd</application> queries
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the <literal>pg_stat_replication</literal> system view and compares
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the nodes present there against the list of nodes registered with &repmgr; which
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should be attached to the primary.
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@@ -233,7 +239,7 @@
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If the <varname>child_nodes_disconnect_command</varname> parameter is set in
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<filename>repmgr.conf</filename>, <application>repmgrd</application> will then loop through all child nodes.
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If it determines that insufficient child nodes are connected, and a
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minimum of <varname>child_nodes_disconnect_timeout</varname> seconds (default: <literal>30</literal>
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minimum of <varname>child_nodes_disconnect_timeout</varname> seconds (default: <literal>30</literal>)
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has elapsed since the last node became disconnected, <application>repmgrd</application> will then execute the
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<varname>child_nodes_disconnect_command</varname> script.
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</para>
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@@ -253,7 +259,8 @@
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the criteria for its execution are met again.
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</para>
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<para>
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The <varname>child_nodes_disconnect_command</varname> script will not be executed if <application>repmgrd</application> is paused.
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The <varname>child_nodes_disconnect_command</varname> script will not be executed if
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<application>repmgrd</application> is paused.
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</para>
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</listitem>
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@@ -266,7 +273,122 @@
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</listitem>
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</itemizedlist>
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</para>
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</para>
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</sect2>
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<sect2 id="repmgrd-primary-child-disconnection-example">
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<title>Standby disconnections monitoring process example</title>
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<para>
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</para>
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</sect2>
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<sect2 id="repmgrd-primary-child-disconnection-configuration">
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<title>Standby disconnections monitoring process configuration</title>
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<para>
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</para>
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</sect2>
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<sect2 id="repmgrd-primary-child-disconnection-events">
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<title>Standby disconnections monitoring process event notifications</title>
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<para>
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The following <link linkend="event-notifications">event notifications</link> may be generated:
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</para>
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<variablelist>
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<varlistentry>
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<indexterm>
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<primary>child_node_disconnect</primary>
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<secondary>event notification</secondary>
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</indexterm>
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<term><varname>child_node_disconnect</varname></term>
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<listitem>
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<para>
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This event is generated after <application>repmgrd</application>
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detects that a child node is no longer streaming from the primary node.
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</para>
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<para>
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Example:
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<programlisting>
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$ repmgr cluster event --event=child_node_disconnect
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Node ID | Name | Event | OK | Timestamp | Details
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---------+-------+-----------------------+----+---------------------+--------------------------------------------
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1 | node1 | child_node_disconnect | t | 2019-04-24 12:41:36 | node "node3" (node ID: 3) has disconnected</programlisting>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<indexterm>
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<primary>child_node_reconnect</primary>
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<secondary>event notification</secondary>
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</indexterm>
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<term><varname>child_node_reconnect</varname></term>
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<listitem>
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<para>
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This event is generated after <application>repmgrd</application>
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detects that a child node has resumed streaming from the primary node.
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</para>
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<para>
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Example:
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<programlisting>
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$ repmgr cluster event --event=child_node_reconnect
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Node ID | Name | Event | OK | Timestamp | Details
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---------+-------+----------------------+----+---------------------+------------------------------------------------------------
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1 | node1 | child_node_reconnect | t | 2019-04-24 12:42:19 | node "node3" (node ID: 3) has reconnected after 42 seconds</programlisting>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<indexterm>
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<primary>child_node_new_connect</primary>
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<secondary>event notification</secondary>
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</indexterm>
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<term><varname>child_node_new_connect</varname></term>
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<listitem>
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<para>
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This event is generated after <application>repmgrd</application>
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detects that a new child node has been registered with &repmgr; and has
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connected to the primary.
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</para>
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<para>
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Example:
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<programlisting>
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$ repmgr cluster event --event=child_node_new_connect
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Node ID | Name | Event | OK | Timestamp | Details
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---------+-------+------------------------+----+---------------------+---------------------------------------------
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1 | node1 | child_node_new_connect | t | 2019-04-24 12:41:30 | new node "node3" (node ID: 3) has connected</programlisting>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<indexterm>
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<primary>child_nodes_disconnect_command</primary>
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<secondary>event notification</secondary>
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</indexterm>
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<term><varname>child_nodes_disconnect_command</varname></term>
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<listitem>
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<para>
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This event is generated after <application>repmgrd</application> detects
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that sufficient child nodes have been disconnected for a sufficient amount
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of time to trigger execution of the <varname>child_nodes_disconnect_command</varname>.
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</para>
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<para>
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Example:
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<programlisting>
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$ repmgr cluster event --event=child_nodes_disconnect_command
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Node ID | Name | Event | OK | Timestamp | Details
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---------+-------+--------------------------------+----+---------------------+--------------------------------------------------------
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1 | node1 | child_nodes_disconnect_command | t | 2019-04-24 13:08:17 | "child_nodes_disconnect_command" successfully executed</programlisting>
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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</sect1>
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