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26th chunk of `doc/src/sgml/monitoring.sgml`
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 <para>
        How many blocks ahead the prefetcher is looking
       </para>
      </entry>
     </row>

     <row>
      <entry role="catalog_table_entry">
       <para role="column_definition">
        <structfield>io_depth</structfield> <type>int</type>
       </para>
       <para>
        How many prefetches have been initiated but are not yet known to have completed
       </para>
      </entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect2>

 <sect2 id="monitoring-pg-stat-subscription">
  <title><structname>pg_stat_subscription</structname></title>

  <indexterm>
   <primary>pg_stat_subscription</primary>
  </indexterm>

  <table id="pg-stat-subscription" xreflabel="pg_stat_subscription">
   <title><structname>pg_stat_subscription</structname> View</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the subscription
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>subname</structfield> <type>name</type>
      </para>
      <para>
       Name of the subscription
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>worker_type</structfield> <type>text</type>
      </para>
      <para>
       Type of the subscription worker process.  Possible types are
       <literal>apply</literal>, <literal>parallel apply</literal>, and
       <literal>table synchronization</literal>.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of the subscription worker process
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>leader_pid</structfield> <type>integer</type>
      </para>
      <para>
       Process ID of the leader apply worker if this process is a parallel
       apply worker; NULL if this process is a leader apply worker or a table
       synchronization worker
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>relid</structfield> <type>oid</type>
      </para>
      <para>
       OID of the relation that the worker is synchronizing; NULL for the
       leader apply worker and parallel apply workers
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>received_lsn</structfield> <type>pg_lsn</type>
      </para>
      <para>
       Last write-ahead log location received, the initial value of
       this field being 0; NULL for parallel apply workers
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_msg_send_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Send time of last message received from origin WAL sender; NULL for
       parallel apply workers
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>last_msg_receipt_time</structfield> <type>timestamp with time zone</type>
      </para>
      <para>
       Receipt time of last message received from origin WAL sender; NULL for
       parallel apply workers
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>latest_end_lsn</structfield>
Title: pg_stat_subscription View Columns Explained
Summary
This section describes the columns of the `pg_stat_subscription` view, which provides information about subscription worker processes. Columns include: `subid` (subscription OID), `subname` (subscription name), `worker_type` (apply, parallel apply, or table synchronization), `pid` (process ID), `leader_pid` (leader apply worker PID), `relid` (relation OID being synchronized), `received_lsn` (last WAL location received), `last_msg_send_time` (send time of last message from origin WAL sender), and `last_msg_receipt_time` (receipt time of last message).