postgresql/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 logical-replication
   subscription.  The subscription name must be distinct from the name of
   any existing subscription in the current database.
  </para>

  <para>
   A subscription represents a replication connection to the publisher.
   Hence, in addition to adding definitions in the local catalogs, this
   command normally 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,
   unless the subscription is initially disabled.
  </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 <application>libpq</application> connection string defining how
      to connect to the publisher database.  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.
     </para>

     <para>
      The following parameters control what happens during subscription creation:

      <variablelist>

       <varlistentry>
        <term><literal>connect</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether the <command>CREATE SUBSCRIPTION</command>
          command should connect to the publisher at all.  The default
          is <literal>true</literal>.  Setting this to
          <literal>false</literal> will force the values of
          <literal>create_slot</literal>, <literal>enabled</literal> and
          <literal>copy_data</literal> to <literal>false</literal>.
          (You cannot combine setting <literal>connect</literal>
          to <literal>false</literal> with
          setting <literal>create_slot</literal>, <literal>enabled</literal>,
          or <literal>copy_data</literal> to <literal>true</literal>.)
         </para>

         <para>
          Since no connection is made when this option is
          <literal>false</literal>, no tables are subscribed, and so
          after you enable the subscription nothing will be replicated.
          You will need to then run
          <literal>ALTER SUBSCRIPTION ... REFRESH PUBLICATION</literal>
          for tables to be subscribed.
         </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>.
          If set to <literal>false</literal>, you are responsible for
          creating the publisher's slot in some other way.
         </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 just be set up 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 publisher's replication slot to use.  The default is
          to use the name of the subscription for the slot name.
         </para>

         <para>
          Setting <literal>slot_name</literal> to <literal>NONE</literal>
          means there will be no replication slot
          associated with the subscription.  Use this when you will be
          creating the replication slot later manually.  Such
          subscriptions must also have both <literal>enabled</literal> and
          <literal>create_slot</literal> set to <literal>false</literal>.
         </para>
        </listitem>
       </varlistentry>
      </variablelist>
     </para>

     <para>
      The following parameters control the subscription's replication
      behavior after it has been created:

      <variablelist>

       <varlistentry>
        <term><literal>binary</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether the subscription will request the publisher to
          send the data in binary format (as opposed to text).
          The default is <literal>false</literal>.
          Even when this option is enabled, only data types having
          binary send and receive functions will be transferred in binary.
         </para>

         <para>
          When doing cross-version replication, it could be that the
          publisher has a binary send function for some data type, but the
          subscriber lacks a binary receive function for that type.  In
          such a case, data transfer will fail, and
          the <literal>binary</literal> option cannot be used.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>copy_data</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether to copy pre-existing data in the publications
          that are being subscribed to when the replication starts.
          The default is <literal>true</literal>.
         </para>
        </listitem>
       </varlistentry>

       <varlistentry>
        <term><literal>streaming</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether to enable streaming of in-progress transactions
          for this subscription.  By default, all transactions
          are fully decoded on the publisher and only then sent to the
          subscriber as a whole.
         </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 within this
          subscription's apply worker processes.  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>two_phase</literal> (<type>boolean</type>)</term>
        <listitem>
         <para>
          Specifies whether two-phase commit is enabled for this subscription.
          The default is <literal>false</literal>.
         </para>

         <para>
          When two-phase commit is enabled, prepared transactions are sent
          to the subscriber at the time of <command>PREPARE
          TRANSACTION</command>, and are processed as two-phase
          transactions on the subscriber too.  Otherwise, prepared
          transactions are sent to the subscriber only when committed, and
          are then processed immediately by the subscriber.
         </para>

         <para>
          The implementation of two-phase commit requires that replication
          has successfully finished the initial table synchronization
          phase. So even when <literal>two_phase</literal> is enabled for a
          subscription, the internal two-phase state remains
          temporarily <quote>pending</quote> until the initialization phase
          completes. See column <structfield>subtwophasestate</structfield>
          of <link linkend="catalog-pg-subscription"><structname>pg_subscription</structname></link>
          to know the actual two-phase state.
         </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>