postgres/doc/src/sgml/ref/create_subscription.sgml

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doc/src/sgml/ref/create_subscription.sgml
PostgreSQL documentation
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<refentry id="sql-createsubscription">
 <indexterm zone="sql-createsubscription">
  <primary>CREATE SUBSCRIPTION</primary>
 </indexterm>

 <refmeta>
  <refentrytitle>CREATE SUBSCRIPTION</refentrytitle>
  <manvolnum>7</manvolnum>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>CREATE SUBSCRIPTION</refname>
  <refpurpose>define a new subscription</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
<synopsis>
CREATE SUBSCRIPTION <replaceable class="parameter">subscription_name</replaceable>
    CONNECTION '<replaceable class="parameter">conninfo</replaceable>'
    PUBLICATION <replaceable class="parameter">publication_name</replaceable> [, ...]
    [ WITH ( <replaceable class="parameter">subscription_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] ) ]
</synopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <command>CREATE SUBSCRIPTION</command> adds a new subscription for the
   current database.  The subscription name must be distinct from the name of
   any existing subscription in the database.
  </para>

  <para>
   The subscription represents a replication connection to the publisher.  As
   such this command does not only add definitions in the local catalogs but
   also creates a replication slot on the publisher.
  </para>

  <para>
   A logical replication worker will be started to replicate data for the new
   subscription at the commit of the transaction where this command is run.
  </para>

  <para>
   Additional information about subscriptions and logical replication as a
   whole is available at <xref linkend="logical-replication-subscription"/> and
   <xref linkend="logical-replication"/>.
  </para>

 </refsect1>

 <refsect1>
  <title>Parameters</title>

  <variablelist>
   <varlistentry>
    <term><replaceable class="parameter">subscription_name</replaceable></term>
    <listitem>
     <para>
      The name of the new subscription.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>CONNECTION '<replaceable class="parameter">conninfo</replaceable>'</literal></term>
    <listitem>
     <para>
      The connection string to the publisher.  For details
      see <xref linkend="libpq-connstring"/>.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>PUBLICATION <replaceable class="parameter">publication_name</replaceable></literal></term>
    <listitem>
     <para>
      Names of the publications on the publisher to subscribe to.
     </para>
    </listitem>
   </varlistentry>

   <varlistentry>
    <term><literal>WITH ( <replaceable class="parameter">subscription_parameter</replaceable> [= <replaceable class="parameter">value</replaceable>] [, ... ] )</literal></term>
    <listitem>
     <para>
      This clause specifies optional parameters for a subscription.  The
      following parameters are supported:

      <variablelist>
       <varlistentry>
        <term><literal>copy_data</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether the existing data in the publications that are
          being subscribed to should be copied once the replication starts.
          The default is <literal>true</literal>.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>create_slot</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether the command should create the replication slot on
          the publisher.  The default is <literal>true</literal>.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>enabled</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether the subscription should be actively replicating,
          or whether it should be just setup but not started yet.  The default
          is <literal>true</literal>.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>slot_name</literal> (<type>string</type>)</term>
        <listitem>
         <para>
          Name of the replication slot to use.  The default behavior is to
          use the name of the subscription for the slot name.
         </para>

         <para>
          When <literal>slot_name</literal> is set to
          <literal>NONE</literal>, there will be no replication slot
          associated with the subscription.  This can be used if the
          replication slot will be created later manually.  Such
          subscriptions must also have both <literal>enabled</literal> and
          <literal>create_slot</literal> set to <literal>false</literal>.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>synchronous_commit</literal> (<type>enum</type>)</term>
        <listitem>
         <para>
          The value of this parameter overrides the
          <xref linkend="guc-synchronous-commit"/> setting.  The default
          value is <literal>off</literal>.
         </para>

         <para>
          It is safe to use <literal>off</literal> for logical replication:
          If the subscriber loses transactions because of missing
          synchronization, the data will be sent again from the publisher.
         </para>

         <para>
          A different setting might be appropriate when doing synchronous
          logical replication.  The logical replication workers report the
          positions of writes and flushes to the publisher, and when using
          synchronous replication, the publisher will wait for the actual
          flush.  This means that setting
          <literal>synchronous_commit</literal> for the subscriber to
          <literal>off</literal> when the subscription is used for
          synchronous replication might increase the latency for
          <command>COMMIT</command> on the publisher.  In this scenario, it
          can be advantageous to set <literal>synchronous_commit</literal>
          to <literal>local</literal> or higher.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>connect</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether the <command>CREATE SUBSCRIPTION</command>
          should connect to the publisher at all.  Setting this to
          <literal>false</literal> will change default values of
          <literal>enabled</literal>, <literal>create_slot</literal> and
          <literal>copy_data</literal> to <literal>false</literal>.
         </para>

         <para>
          It is not allowed to combine <literal>connect</literal> set to
          <literal>false</literal> and <literal>enabled</literal>,
          <literal>create_slot</literal>, or <literal>copy_data</literal>
          set to <literal>true</literal>.
         </para>

         <para>
          Since no connection is made when this option is set
          to <literal>false</literal>, the tables are not subscribed, and so
          after you enable the subscription nothing will be replicated.
          It is required to run
          <literal>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</literal> in order
          for tables to be subscribed.
         </para>
        </listitem>
       </varlistentry>
      </variablelist></para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   See <xref linkend="logical-replication-security"/> for details on
   how to configure access control between the subscription and the
   publication instance.
  </para>

  <para>
   When creating a replication slot (the default behavior), <command>CREATE
   SUBSCRIPTION</command> cannot be executed inside a transaction block.
  </para>

  <para>
   Creating a subscription that connects to the same database cluster (for
   example, to replicate between databases in the same cluster or to replicate
   within the same database) will only succeed if the replication slot is not
   created as part of the same command.  Otherwise, the <command>CREATE
   SUBSCRIPTION</command> call will hang.  To make this work, create the
   replication slot separately (using the
   function <function>pg_create_logical_replication_slot</function> with the
   plugin name <literal>pgoutput</literal>) and create the subscription using
   the parameter <literal>create_slot = false</literal>.  This is an
   implementation restriction that might be lifted in a future release.
  </para>
 </refsect1>

 <refsect1>
  <title>Examples</title>

  <para>
   Create a subscription to a remote server that replicates tables in
   the publications <literal>mypublication</literal> and
   <literal>insert_only</literal> and starts replicating immediately on
   commit:
<programlisting>
CREATE SUBSCRIPTION mysub
         CONNECTION 'host=192.168.1.50 port=5432 user=foo dbname=foodb'
        PUBLICATION mypublication, insert_only;
</programlisting>
  </para>

  <para>
   Create a subscription to a remote server that replicates tables in
   the <literal>insert_only</literal> publication and does not start replicating
   until enabled at a later time.
<programlisting>
CREATE SUBSCRIPTION mysub
         CONNECTION 'host=192.168.1.50 port=5432 user=foo dbname=foodb'
        PUBLICATION insert_only
               WITH (enabled = false);
</programlisting></para>
 </refsect1>

 <refsect1>
  <title>Compatibility</title>

  <para>
   <command>CREATE SUBSCRIPTION</command> is a <productname>PostgreSQL</productname>
   extension.
  </para>
 </refsect1>

 <refsect1>
  <title>See Also</title>

  <simplelist type="inline">
   <member><xref linkend="sql-altersubscription"/></member>
   <member><xref linkend="sql-dropsubscription"/></member>
   <member><xref linkend="sql-createpublication"/></member>
   <member><xref linkend="sql-alterpublication"/></member>
  </simplelist>
 </refsect1>
</refentry>