<!--
doc/src/sgml/ref/pgupgrade.sgml
PostgreSQL documentation
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<refentry id="pgupgrade">
 <indexterm zone="pgupgrade">
  <primary>pg_upgrade</primary>
 </indexterm>

 <refmeta>
  <refentrytitle><application>pg_upgrade</application></refentrytitle>
  <manvolnum>1</manvolnum>
  <refmiscinfo>Application</refmiscinfo>
 </refmeta>

 <refnamediv>
  <refname>pg_upgrade</refname>
  <refpurpose>upgrade a <productname>PostgreSQL</productname> server instance</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  <cmdsynopsis>
   <command>pg_upgrade</command>
   <arg choice="plain"><option>-b</option></arg>
   <arg choice="plain"><replaceable>oldbindir</replaceable></arg>
   <arg choice="opt"><option>-B</option> <replaceable>newbindir</replaceable></arg>
   <arg choice="plain"><option>-d</option></arg>
   <arg choice="plain"><replaceable>oldconfigdir</replaceable></arg>
   <arg choice="plain"><option>-D</option></arg>
   <arg choice="plain"><replaceable>newconfigdir</replaceable></arg>
   <arg rep="repeat"><replaceable>option</replaceable></arg>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

 <para>
  <application>pg_upgrade</application> (formerly called <application>pg_migrator</application>) allows data
  stored in <productname>PostgreSQL</productname> data files to be upgraded to a later <productname>PostgreSQL</productname>
  major version without the data dump/restore typically required for
  major version upgrades, e.g., from 12.14 to 13.10 or from 14.9 to 15.5.
  It is not required for minor version upgrades, e.g., from 12.7 to 12.8
  or from 14.1 to 14.5.
 </para>

 <para>
  Major PostgreSQL releases regularly add new features that often
  change the layout of the system tables, but the internal data storage
  format rarely changes.  <application>pg_upgrade</application> uses this fact
  to perform rapid upgrades by creating new system tables and simply
  reusing the old user data files.  If a future major release ever
  changes the data storage format in a way that makes the old data
  format unreadable, <application>pg_upgrade</application> will not be usable
  for such upgrades.  (The community will attempt to avoid such
  situations.)
 </para>

 <para>
  <application>pg_upgrade</application> does its best to
  make sure the old and new clusters are binary-compatible, e.g.,  by
  checking for compatible compile-time settings, including 32/64-bit
  binaries.  It is important that
  any external modules are also binary compatible, though this cannot
  be checked by <application>pg_upgrade</application>.
 </para>

  <para>
   <application>pg_upgrade</application> supports upgrades from 9.2.X and later to the current
   major release of <productname>PostgreSQL</productname>, including snapshot and beta releases.
  </para>

  <warning>
   <para>
    Upgrading a cluster causes the destination to execute arbitrary code of the
    source superusers' choice.  Ensure that the source superusers are trusted
    before upgrading.
   </para>
  </warning>
 </refsect1>

 <refsect1>
  <title>Options</title>

   <para>
    <application>pg_upgrade</application> accepts the following command-line arguments:

    <variablelist>

     <varlistentry>
      <term><option>-b</option> <replaceable>bindir</replaceable></term>
      <term><option>--old-bindir=</option><replaceable>bindir</replaceable></term>
      <listitem><para>the old PostgreSQL executable directory;
      environment variable <envar>PGBINOLD</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-B</option> <replaceable>bindir</replaceable></term>
      <term><option>--new-bindir=</option><replaceable>bindir</replaceable></term>
      <listitem><para>the new PostgreSQL executable directory;
      default is the directory where <application>pg_upgrade</application> resides;
      environment variable <envar>PGBINNEW</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-c</option></term>
      <term><option>--check</option></term>
      <listitem><para>check clusters only, don't change any data</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-d</option> <replaceable>configdir</replaceable></term>
      <term><option>--old-datadir=</option><replaceable>configdir</replaceable></term>
      <listitem><para>the old database cluster configuration directory; environment
      variable <envar>PGDATAOLD</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-D</option> <replaceable>configdir</replaceable></term>
      <term><option>--new-datadir=</option><replaceable>configdir</replaceable></term>
      <listitem><para>the new database cluster configuration directory; environment
      variable <envar>PGDATANEW</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-j <replaceable class="parameter">njobs</replaceable></option></term>
      <term><option>--jobs=<replaceable class="parameter">njobs</replaceable></option></term>
      <listitem><para>number of simultaneous connections and processes/threads to use
      </para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-k</option></term>
      <term><option>--link</option></term>
      <listitem><para>use hard links instead of copying files to the new
      cluster</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-N</option></term>
      <term><option>--no-sync</option></term>
      <listitem>
       <para>
        By default, <command>pg_upgrade</command> will wait for all files
        of the upgraded cluster to be written safely to disk.  This option
        causes <command>pg_upgrade</command> to return without waiting, which
        is faster, but means that a subsequent operating system crash can leave
        the data directory corrupt.  Generally, this option is
        useful for testing but should not be used on a production
        installation.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-o</option> <replaceable class="parameter">options</replaceable></term>
      <term><option>--old-options</option> <replaceable class="parameter">options</replaceable></term>
      <listitem><para>options to be passed directly to the
      old <command>postgres</command> command;  multiple
      option invocations are appended</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-O</option> <replaceable class="parameter">options</replaceable></term>
      <term><option>--new-options</option> <replaceable class="parameter">options</replaceable></term>
      <listitem><para>options to be passed directly to the
      new <command>postgres</command> command;  multiple
      option invocations are appended</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-p</option> <replaceable>port</replaceable></term>
      <term><option>--old-port=</option><replaceable>port</replaceable></term>
      <listitem><para>the old cluster port number; environment
      variable <envar>PGPORTOLD</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-P</option> <replaceable>port</replaceable></term>
      <term><option>--new-port=</option><replaceable>port</replaceable></term>
      <listitem><para>the new cluster port number; environment
      variable <envar>PGPORTNEW</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-r</option></term>
      <term><option>--retain</option></term>
      <listitem><para>retain SQL and log files even after successful completion
      </para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-s</option> <replaceable>dir</replaceable></term>
      <term><option>--socketdir=</option><replaceable>dir</replaceable></term>
      <listitem><para>directory to use for postmaster sockets during upgrade;
      default is current working directory; environment
      variable <envar>PGSOCKETDIR</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-U</option> <replaceable>username</replaceable></term>
      <term><option>--username=</option><replaceable>username</replaceable></term>
      <listitem><para>cluster's install user name; environment
      variable <envar>PGUSER</envar></para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-v</option></term>
      <term><option>--verbose</option></term>
      <listitem><para>enable verbose internal logging</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-V</option></term>
      <term><option>--version</option></term>
      <listitem><para>display version information, then exit</para></listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--clone</option></term>
      <listitem>
       <para>
        Use efficient file cloning (also known as <quote>reflinks</quote> on
        some systems) instead of copying files to the new cluster.  This can
        result in near-instantaneous copying of the data files, giving the
        speed advantages of <option>-k</option>/<option>--link</option> while
        leaving the old cluster untouched.
       </para>

       <para>
        File cloning is only supported on some operating systems and file
        systems.  If it is selected but not supported, the
        <application>pg_upgrade</application> run will error.  At present, it
        is supported on Linux (kernel 4.5 or later) with Btrfs and XFS (on
        file systems created with reflink support), and on macOS with APFS.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--copy</option></term>
      <listitem>
       <para>
        Copy files to the new cluster.  This is the default.  (See also
        <option>--link</option>, <option>--clone</option>,
        <option>--copy-file-range</option>, and <option>--swap</option>.)
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--copy-file-range</option></term>
      <listitem>
       <para>
        Use the <function>copy_file_range</function> system call for efficient
        copying.  On some file systems this gives results similar to
        <option>--clone</option>, sharing physical disk blocks, while on others
        it may still copy blocks, but do so via an optimized path.  At present,
        it is supported on Linux and FreeBSD.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--no-statistics</option></term>
      <listitem>
       <para>
        Do not restore statistics from the old cluster into the new cluster.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--set-char-signedness=</option><replaceable>option</replaceable></term>
      <listitem>
       <para>
        Manually set the default char signedness of new clusters. Possible values
        are <literal>signed</literal> and <literal>unsigned</literal>.
       </para>
       <para>
        In the C language, the default signedness of the <type>char</type> type
        (when not explicitly specified) varies across platforms. For example,
        <type>char</type> defaults to <type>signed char</type> on x86 CPUs but
        to <type>unsigned char</type> on ARM CPUs.
       </para>
       <para>
        Starting from <productname>PostgreSQL</productname> 18, database clusters
        maintain their own default char signedness setting, which can be used to
        ensure consistent behavior across platforms with different default char
        signedness. By default, <application>pg_upgrade</application> preserves
        the char signedness setting when upgrading from an existing cluster.
        However, when upgrading from <productname>PostgreSQL</productname> 17 or
        earlier, <application>pg_upgrade</application> adopts the char signedness
        of the platform on which it was built.
       </para>
       <para>
        This option allows you to explicitly set the default char signedness for
        the new cluster, overriding any inherited values. There are two specific
        scenarios where this option is relevant:
        <itemizedlist>
         <listitem>
          <para>
           If you are planning to migrate to a different platform after the upgrade,
           you should not use this option. The default behavior is right in this case.
           Instead, perform the upgrade on the original platform without this flag,
           and then migrate the cluster afterward. This is the recommended and safest
           approach.
          </para>
         </listitem>
         <listitem>
          <para>
           If you have already migrated the cluster to a platform with different
           char signedness (for example, from an x86-based system to an ARM-based
           system), you should use this option to specify the signedness matching
           the original platform's default char signedness. Additionally, it's
           essential not to modify any data files between migrating data files and
           running <command>pg_upgrade</command>. <command>pg_upgrade</command>
           should be the first operation that starts the cluster on the new platform.
          </para>
         </listitem>
        </itemizedlist>
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--swap</option></term>
      <listitem>
       <para>
        Move the data directories from the old cluster to the new cluster.
        Then, replace the catalog files with those generated for the new
        cluster.  This mode can outperform <option>--link</option>,
        <option>--clone</option>, <option>--copy</option>, and
        <option>--copy-file-range</option>, especially on clusters with many
        relations.
       </para>
       <para>
        However, this mode creates many garbage files in the old cluster, which
        can prolong the file synchronization step if
        <option>--sync-method=syncfs</option> is used.  Therefore, it is
        recommended to use <option>--sync-method=fsync</option> with
        <option>--swap</option>.
       </para>
       <para>
        Additionally, once the file transfer step begins, the old cluster will
        be destructively modified and therefore will no longer be safe to
        start.  See <xref linkend="pgupgrade-step-revert"/> for details.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>--sync-method=</option><replaceable>method</replaceable></term>
      <listitem>
       <para>
        When set to <literal>fsync</literal>, which is the default,
        <command>pg_upgrade</command> will recursively open and synchronize all
        files in the upgraded cluster's data directory.  The search for files
        will follow symbolic links for the WAL directory and each configured
        tablespace.
       </para>
       <para>
        On Linux, <literal>syncfs</literal> may be used instead to ask the
        operating system to synchronize the whole file systems that contain the
        upgraded cluster's data directory, its WAL files, and each tablespace.
        See <xref linkend="guc-recovery-init-sync-method"/> for information
        about the caveats to be aware of when using <literal>syncfs</literal>.
       </para>
       <para>
        This option has no effect when <option>--no-sync</option> is used.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term><option>-?</option></term>
      <term><option>--help</option></term>
      <listitem><para>show help, then exit</para></listitem>
     </varlistentry>

    </variablelist>
   </para>

 </refsect1>

 <refsect1>
  <title>Usage</title>

  <para>
   These are the steps to perform an upgrade
   with <application>pg_upgrade</application>:
  </para>

   <note>
    <para>
     The steps to upgrade <glossterm linkend="glossary-logical-replication-cluster">logical replication clusters</glossterm>
     are not covered here;
     refer to <xref linkend="logical-replication-upgrade"/> for details.
    </para>
   </note>

  <procedure>
   <step performance="optional">
    <title>Optionally move the old cluster</title>

    <para>
     If you are using a version-specific installation directory, e.g.,
     <filename>/opt/PostgreSQL/&majorversion;</filename>, you do not need to move the old cluster. The
     graphical installers all use version-specific installation directories.
    </para>

    <para>
     If your installation directory is not version-specific, e.g.,
     <filename>/usr/local/pgsql</filename>, it is necessary to move the current PostgreSQL install
     directory so it does not interfere with the new <productname>PostgreSQL</productname> installation.
     Once the current <productname>PostgreSQL</productname> server is shut down, it is safe to rename the
     PostgreSQL installation directory; assuming the old directory is
     <filename>/usr/local/pgsql</filename>, you can do:

<programlisting>
mv /usr/local/pgsql /usr/local/pgsql.old
</programlisting>
     to rename the directory.
    </para>
   </step>

   <step>
    <title>For source installs, build the new version</title>

    <para>
     Build the new PostgreSQL source with <command>configure</command> flags that are compatible
     with the old cluster. <application>pg_upgrade</application> will check <command>pg_controldata</command> to make
     sure all settings are compatible before starting the upgrade.
    </para>
   </step>

   <step>
    <title>Install the new PostgreSQL binaries</title>

    <para>
     Install the new server's binaries and support
     files.  <application>pg_upgrade</application> is included in a default installation.
    </para>

    <para>
     For source installs, if you wish to install the new server in a custom
     location, use the <literal>prefix</literal> variable:

<programlisting>
make prefix=/usr/local/pgsql.new install
</programlisting></para>
   </step>

   <step>
    <title>Initialize the new PostgreSQL cluster</title>

    <para>
     Initialize the new cluster using <command>initdb</command>.
     Again, use compatible <command>initdb</command>
     flags that match the old cluster. Many
     prebuilt installers do this step automatically. There is no need to
     start the new cluster.
    </para>
   </step>

   <step>
    <title>Install extension shared object files</title>

    <para>
     Many extensions and custom modules, whether from
     <filename>contrib</filename> or another source, use shared object
     files (or DLLs), e.g., <filename>pgcrypto.so</filename>.  If the old
     cluster used these, shared object files matching the new server binary
     must be installed in the new cluster, usually via operating system
     commands.  Do not load the schema definitions, e.g., <command>CREATE
     EXTENSION pgcrypto</command>, because these will be duplicated from
     the old cluster.  If extension updates are available,
     <application>pg_upgrade</application> will report this and create
     a script that can be run later to update them.
    </para>
   </step>

   <step>
    <title>Copy custom full-text search files</title>

    <para>
     Copy any custom full text search files (dictionary, synonym,
     thesaurus, stop words) from the old to the new cluster.
    </para>
   </step>

   <step>
    <title>Adjust authentication</title>

    <para>
     <command>pg_upgrade</command> will connect to the old and new servers several
     times, so you might want to set authentication to <literal>peer</literal>
     in <filename>pg_hba.conf</filename> or use a <filename>~/.pgpass</filename> file
     (see <xref linkend="libpq-pgpass"/>).
    </para>
   </step>

   <step>
    <title>Stop both servers</title>

    <para>
     Make sure both database servers are stopped using, on Unix, e.g.:

<programlisting>
pg_ctl -D /opt/PostgreSQL/12 stop
pg_ctl -D /opt/PostgreSQL/&majorversion; stop
</programlisting>

     or on Windows, using the proper service names:

<programlisting>
NET STOP postgresql-12
NET STOP postgresql-&majorversion;
</programlisting>
    </para>

    <para>
     Streaming replication and log-shipping standby servers must be
     running during this shutdown so they receive all changes.
    </para>
   </step>

   <step>
    <title>Prepare for standby server upgrades</title>

    <para>
     If you are upgrading standby servers using methods outlined in section <xref
     linkend="pgupgrade-step-replicas"/>, verify that the old standby
     servers are caught up by running <application>pg_controldata</application>
     against the old primary and standby clusters.  Verify that the
     <quote>Latest checkpoint location</quote> values match in all clusters.
     Also, make sure <varname>wal_level</varname> is not set to
     <literal>minimal</literal> in the <filename>postgresql.conf</filename> file on the
     new primary cluster.
    </para>
   </step>

   <step>
    <title>Run <application>pg_upgrade</application></title>

    <para>
     Always run the <application>pg_upgrade</application> binary of the new server, not the old one.
     <application>pg_upgrade</application> requires the specification of the old and new cluster's
     data and executable (<filename>bin</filename>) directories. You can also specify
     user and port values, and whether you want the data files linked, cloned, or swapped
     instead of the default copy behavior.
    </para>

    <para>
     If you use link mode, the upgrade will be much faster (no file
     copying) and use less disk space, but you will not be able to access
     your old cluster
     once you start the new cluster after the upgrade.  Link mode also
     requires that the old and new cluster data directories be in the
     same file system.  (Tablespaces and <filename>pg_wal</filename> can be on
     different file systems.)
     Clone mode provides the same speed and disk space advantages but
     does not cause the old cluster to be unusable once the new cluster
     is started.  Clone mode also requires that the old and new data
     directories be in the same file system.  This mode is only available
     on certain operating systems and file systems.
     Swap mode may be the fastest if there are many relations, but you will not
     be able to access your old cluster once the file transfer step begins.
     Swap mode also requires that the old and new cluster data directories be
     in the same file system.
    </para>

    <para>
     Setting <option>--jobs</option> to 2 or higher allows pg_upgrade to
     process multiple databases and tablespaces in parallel.  A good starting
     point is the number of CPU cores on the machine.  This option can
     substantially reduce the upgrade time for multi-database and
     multi-tablespace servers.
    </para>

    <para>
     For Windows users, you must be logged into an administrative account,
     and then run <application>pg_upgrade</application> with quoted
     directories, e.g.:

<programlisting>
pg_upgrade.exe
        --old-datadir "C:/Program Files/PostgreSQL/12/data"
        --new-datadir "C:/Program Files/PostgreSQL/&majorversion;/data"
        --old-bindir "C:/Program Files/PostgreSQL/12/bin"
        --new-bindir "C:/Program Files/PostgreSQL/&majorversion;/bin"
</programlisting>

     Once started, <command>pg_upgrade</command> will verify the two clusters are compatible
     and then do the upgrade. You can use <command>pg_upgrade --check</command>
     to perform only the checks, even if the old server is still
     running. <command>pg_upgrade --check</command> will also outline any
     manual adjustments you will need to make after the upgrade.  If you
     are going to be using link, clone, copy-file-range, or swap mode, you
     should use the option <option>--link</option>, <option>--clone</option>,
     <option>--copy-file-range</option>, or <option>--swap</option> with
     <option>--check</option> to enable mode-specific checks.
     <command>pg_upgrade</command> requires write permission in the current directory.
    </para>

    <para>
     Obviously, no one should be accessing the clusters during the
     upgrade.  <application>pg_upgrade</application> defaults to running servers
     on port 50432 to avoid unintended client connections.
     You can use the same port number for both clusters when doing an
     upgrade because the old and new clusters will not be running at the
     same time.  However, when checking an old running server, the old
     and new port numbers must be different.
    </para>

    <para>
     If an error occurs while restoring the database schema, <command>pg_upgrade</command> will
     exit and you will have to revert to the old cluster as outlined in <xref linkend="pgupgrade-step-revert"/>
     below. To try <command>pg_upgrade</command> again, you will need to modify the old
     cluster so the pg_upgrade schema restore succeeds. If the problem is a
     <filename>contrib</filename> module, you might need to uninstall the <filename>contrib</filename> module from
     the old cluster and install it in the new cluster after the upgrade,
     assuming the module is not being used to store user data.
    </para>
   </step>

   <step id="pgupgrade-step-replicas">
    <title>Upgrade streaming replication and log-shipping standby servers</title>

    <para>
     If you used link mode and have Streaming Replication (see <xref
     linkend="streaming-replication"/>) or Log-Shipping (see <xref
     linkend="warm-standby"/>) standby servers, you can follow these steps to
     quickly upgrade them.  You will not be running <application>pg_upgrade</application> on
     the standby servers, but rather <application>rsync</application> on the primary.
     Do not start any servers yet.
    </para>

    <para>
     If you did <emphasis>not</emphasis> use link mode, do not have or do not
     want to use <application>rsync</application>, or want an easier solution, skip
     the instructions in this section and simply recreate the standby
     servers once <application>pg_upgrade</application> completes and the new primary
     is running.
    </para>

    <procedure>

     <step>
      <title>Install the new PostgreSQL binaries on standby servers</title>

      <para>
       Make sure the new binaries and support files are installed on all
       standby servers.
      </para>
     </step>

     <step>
      <title>Make sure the new standby data directories do <emphasis>not</emphasis> exist</title>

      <para>
       Make sure the new standby data directories do <emphasis>not</emphasis>
       exist or are empty.  If <application>initdb</application> was run, delete
       the standby servers' new data directories.
      </para>
     </step>

     <step>
      <title>Install extension shared object files</title>

      <para>
       Install the same extension shared object files on the new standbys
       that you installed in the new primary cluster.
      </para>
     </step>

     <step>
      <title>Stop standby servers</title>

      <para>
       If the standby servers are still running, stop them now using the
       above instructions.
      </para>
     </step>

     <step>
      <title>Save configuration files</title>

      <para>
       Save any configuration files from the old standbys' configuration
       directories you need to keep, e.g.,  <filename>postgresql.conf</filename>
       (and any files included by it), <filename>postgresql.auto.conf</filename>,
       <literal>pg_hba.conf</literal>, because these will be overwritten
       or removed in the next step.
      </para>
     </step>

     <step>
      <title>Run <application>rsync</application></title>

      <para>
       When using link mode, standby servers can be quickly upgraded using
       <application>rsync</application>.  To accomplish this, from a directory on
       the primary server that is above the old and new database cluster
       directories, run this on the <emphasis>primary</emphasis> for each standby
       server:

<programlisting>
rsync --archive --delete --hard-links --size-only --no-inc-recursive old_cluster new_cluster remote_dir
</programlisting>

       where <option>old_cluster</option> and <option>new_cluster</option> are relative
       to the current directory on the primary, and <option>remote_dir</option>
       is <emphasis>above</emphasis> the old and new cluster directories
       on the standby.  The directory structure under the specified
       directories on the primary and standbys must match.  Consult the
       <application>rsync</application> manual page for details on specifying the
       remote directory, e.g.,

<programlisting>
rsync --archive --delete --hard-links --size-only --no-inc-recursive /opt/PostgreSQL/12 \
      /opt/PostgreSQL/&majorversion; standby.example.com:/opt/PostgreSQL
</programlisting>

       You can verify what the command will do using
       <application>rsync</application>'s <option>--dry-run</option> option.  While
       <application>rsync</application> must be run on the primary for at least one
       standby, it is possible to run <application>rsync</application> on an upgraded
       standby to upgrade other standbys, as long as the upgraded standby
       has not been started.
      </para>

      <para>
       What this does is to record the links created by
       <application>pg_upgrade</application>'s link mode that connect files in the
       old and new clusters on the primary server.  It then finds matching
       files in the standby's old cluster and creates links for them in the
       standby's new cluster.  Files that were not linked on the primary
       are copied from the primary to the standby.  (They are usually
       small.)  This provides rapid standby upgrades.  Unfortunately,
       <application>rsync</application> needlessly copies files associated with
       temporary and unlogged tables because these files don't normally
       exist on standby servers.
      </para>

      <para>
       If you have tablespaces, you will need to run a similar
       <application>rsync</application> command for each tablespace directory, e.g.:

<programlisting>
rsync --archive --delete --hard-links --size-only --no-inc-recursive /vol1/pg_tblsp/PG_12_201909212 \
      /vol1/pg_tblsp/PG_&majorversion;_202307071 standby.example.com:/vol1/pg_tblsp
</programlisting>

       If you have relocated <filename>pg_wal</filename> outside the data
       directories, <application>rsync</application> must be run on those directories
       too.
      </para>
     </step>

     <step>
      <title>Configure streaming replication and log-shipping standby servers</title>

      <para>
       Configure the servers for log shipping.  (You do not need to run
       <function>pg_backup_start()</function> and <function>pg_backup_stop()</function>
       or take a file system backup as the standbys are still synchronized
       with the primary.) If the old primary is prior to version 17.0, then no
       slots on the primary are copied to the new standby, so all the slots on
       the old standby must be recreated manually. If the old primary is
       version 17.0 or later, then only logical slots on the primary are copied
       to the new standby, but other slots on the old standby are not copied,
       so must be recreated manually.
      </para>
     </step>

    </procedure>

   </step>

   <step>
    <title>Restore <filename>pg_hba.conf</filename></title>

    <para>
     If you modified <filename>pg_hba.conf</filename>, restore its original settings.
     It might also be necessary to adjust other configuration files in the new
     cluster to match the old cluster, e.g., <filename>postgresql.conf</filename>
     (and any files included by it), <filename>postgresql.auto.conf</filename>.
    </para>
   </step>

   <step>
    <title>Start the new server</title>

    <para>
     The new server can now be safely started, and then any
     <application>rsync</application>'ed standby servers.
    </para>
   </step>

   <step>
    <title>Post-upgrade processing</title>

    <para>
     If any post-upgrade processing is required, pg_upgrade will issue
     warnings as it completes. It will also generate script files that must
     be run by the administrator. The script files will connect to each
     database that needs post-upgrade processing. Each script should be
     run using:

<programlisting>
psql --username=postgres --file=script.sql postgres
</programlisting>

     The scripts can be run in any order and can be deleted once they have
     been run.
    </para>

    <caution>
    <para>
     In general it is unsafe to access tables referenced in rebuild scripts
     until the rebuild scripts have run to completion; doing so could yield
     incorrect results or poor performance. Tables not referenced in rebuild
     scripts can be accessed immediately.
    </para>
    </caution>
   </step>

   <step>
    <title>Statistics</title>

    <para>
     Unless the <option>--no-statistics</option> option is specified,
     <command>pg_upgrade</command> will transfer most optimizer statistics
     from the old cluster to the new cluster.  This does not transfer
     all statistics, such as those created explicitly with
     <xref linkend="sql-createstatistics"/>, custom statistics added by
     an extension, or statistics collected by the cumulative statistics system.
    </para>

    <para>
     Because not all statistics are transferred by
     <command>pg_upgrade</command>, you will be instructed to run commands to
     regenerate that information at the end of the upgrade.  You might need to
     set connection parameters to match your new cluster.
    </para>

    <para>
     First, use
     <command>vacuumdb --all --analyze-in-stages --missing-stats-only</command>
     to quickly generate minimal optimizer statistics for relations without
     any.  Then, use <command>vacuumdb --all --analyze-only</command> to ensure
     all relations have updated cumulative statistics for triggering vacuum and
     analyze.  For both commands, the use of <option>--jobs</option> can speed
     it up.
     If <varname>vacuum_cost_delay</varname> is set to a non-zero
     value, this can be overridden to speed up statistics generation
     using <envar>PGOPTIONS</envar>, e.g., <literal>PGOPTIONS='-c
     vacuum_cost_delay=0' vacuumdb ...</literal>.
    </para>
   </step>

   <step>
    <title>Delete old cluster</title>

    <para>
     Once you are satisfied with the upgrade, you can delete the old
     cluster's data directories by running the script mentioned when
     <command>pg_upgrade</command> completes. (Automatic deletion is not
     possible if you have user-defined tablespaces inside the old data
     directory.)  You can also delete the old installation directories
     (e.g., <filename>bin</filename>, <filename>share</filename>).
    </para>
   </step>

   <step id="pgupgrade-step-revert" performance="optional">
    <title>Reverting to old cluster</title>

    <para>
     If, after running <command>pg_upgrade</command>, you wish to revert to the old cluster,
     there are several options:

     <itemizedlist>
      <listitem>
       <para>
        If the <option>--check</option> option was used, the old cluster
        was unmodified;  it can be restarted.
       </para>
      </listitem>

      <listitem>
       <para>
        If neither <option>--link</option> nor <option>--swap</option> was
        used, the old cluster was unmodified;  it can be restarted.
       </para>
      </listitem>

      <listitem>
       <para>
        If the <option>--link</option> option was used, the data
        files might be shared between the old and new cluster:

        <itemizedlist>
         <listitem>
          <para>
           If <command>pg_upgrade</command> aborted before linking started,
           the old cluster was unmodified;  it can be restarted.
          </para>
         </listitem>

         <listitem>
          <para>
           If you did <emphasis>not</emphasis> start the new cluster, the old
           cluster was unmodified except that, when linking started, a
           <literal>.old</literal> suffix was appended to
           <filename>$PGDATA/global/pg_control</filename>.  To reuse the old
           cluster, remove the <filename>.old</filename> suffix from
           <filename>$PGDATA/global/pg_control</filename>; you can then restart
           the old cluster.
          </para>
         </listitem>

         <listitem>
          <para>
           If you did start the new cluster, it has written to shared files
           and it is unsafe to use the old cluster.  The old cluster will
           need to be restored from backup in this case.
          </para>
         </listitem>

        </itemizedlist></para>
      </listitem>

      <listitem>
       <para>
        If the <option>--swap</option> option was used, the old cluster might
        be destructively modified:

        <itemizedlist>
         <listitem>
          <para>
           If <command>pg_upgrade</command> aborts before reporting that the
           old cluster is no longer safe to start, the old cluster was
           unmodified; it can be restarted.
          </para>
         </listitem>

         <listitem>
          <para>
           If <command>pg_upgrade</command> has reported that the old cluster
           is no longer safe to start, the old cluster was destructively
           modified.  The old cluster will need to be restored from backup in
           this case.
          </para>
         </listitem>
        </itemizedlist>
       </para>
      </listitem>
     </itemizedlist></para>
   </step>
  </procedure>

 </refsect1>

 <refsect1>
  <title>Environment</title>

  <para>
   Some environment variables can be used to provide defaults for command-line options:

   <variablelist>
    <varlistentry>
     <term><envar>PGBINOLD</envar></term>

     <listitem>
      <para>
       The old PostgreSQL executable directory; option
       <option>-b</option>/<option>--old-bindir</option>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><envar>PGBINNEW</envar></term>

     <listitem>
      <para>
       The new PostgreSQL executable directory; option
       <option>-B</option>/<option>--new-bindir</option>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><envar>PGDATAOLD</envar></term>

     <listitem>
      <para>
       The old database cluster configuration directory; option
       <option>-d</option>/<option>--old-datadir</option>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><envar>PGDATANEW</envar></term>

     <listitem>
      <para>
       The new database cluster configuration directory; option
       <option>-D</option>/<option>--new-datadir</option>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><envar>PGPORTOLD</envar></term>

     <listitem>
      <para>
       The old cluster port number; option
       <option>-p</option>/<option>--old-port</option>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><envar>PGPORTNEW</envar></term>

     <listitem>
      <para>
       The new cluster port number; option
       <option>-P</option>/<option>--new-port</option>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><envar>PGSOCKETDIR</envar></term>

     <listitem>
      <para>
       Directory to use for postmaster sockets during upgrade; option
       <option>-s</option>/<option>--socketdir</option>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><envar>PGUSER</envar></term>

     <listitem>
      <para>
       Cluster's install user name; option
       <option>-U</option>/<option>--username</option>.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   <application>pg_upgrade</application> creates various working files, such
   as schema dumps, stored within <filename>pg_upgrade_output.d</filename> in
   the directory of the new cluster. Each run creates a new subdirectory named
   with a timestamp formatted as per ISO 8601
   (<literal>%Y%m%dT%H%M%S</literal>), where all its generated files are
   stored.
   <filename>pg_upgrade_output.d</filename> and its contained files will be
   removed automatically if <application>pg_upgrade</application> completes
   successfully; but in the event of trouble, the files there may provide
   useful debugging information.
  </para>

  <para>
   <application>pg_upgrade</application> launches short-lived postmasters in
   the old and new data directories.  Temporary Unix socket files for
   communication with these postmasters are, by default, made in the current
   working directory.  In some situations the path name for the current
   directory might be too long to be a valid socket name.  In that case you
   can use the <option>-s</option> option to put the socket files in some
   directory with a shorter path name.  For security, be sure that that
   directory is not readable or writable by any other users.
   (This is not supported on Windows.)
  </para>

  <para>
   All failure, rebuild, and reindex cases will be reported by
   <application>pg_upgrade</application> if they affect your installation;
   post-upgrade scripts to rebuild tables and indexes will be
   generated automatically.  If you are trying to automate the upgrade
   of many clusters, you should find that clusters with identical database
   schemas require the same post-upgrade steps for all cluster upgrades;
   this is because the post-upgrade steps are based on the database
   schemas, and not user data.
  </para>

  <para>
   For deployment testing, create a schema-only copy of the old cluster,
   insert dummy data, and upgrade that.
  </para>

  <para>
   <application>pg_upgrade</application> does not support upgrading of databases
   containing table columns using these <type>reg*</type> OID-referencing system data types:
   <simplelist>
    <member><type>regcollation</type></member>
    <member><type>regconfig</type></member>
    <member><type>regdictionary</type></member>
    <member><type>regnamespace</type></member>
    <member><type>regoper</type></member>
    <member><type>regoperator</type></member>
    <member><type>regproc</type></member>
    <member><type>regprocedure</type></member>
   </simplelist>
   (<type>regclass</type>, <type>regrole</type>, and <type>regtype</type> can be upgraded.)
  </para>

  <para>
   If you want to use link mode and you do not want your old cluster
   to be modified when the new cluster is started, consider using the clone mode.
   If that is not available, make a copy of the
   old cluster and upgrade that in link mode. To make a valid copy
   of the old cluster, use <command>rsync</command> to create a dirty
   copy of the old cluster while the server is running, then shut down
   the old server and run <command>rsync --checksum</command> again to update the
   copy with any changes to make it consistent.  (<option>--checksum</option>
   is necessary because <command>rsync</command> only has file modification-time
   granularity of one second.)  You might want to exclude some
   files, e.g., <filename>postmaster.pid</filename>, as documented in <xref
   linkend="backup-lowlevel-base-backup"/>.  If your file system supports
   file system snapshots or copy-on-write file copies, you can use that
   to make a backup of the old cluster and tablespaces, though the snapshot
   and copies must be created simultaneously or while the database server
   is down.
  </para>

 </refsect1>

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

  <simplelist type="inline">
   <member><xref linkend="app-initdb"/></member>
   <member><xref linkend="app-pg-ctl"/></member>
   <member><xref linkend="app-pgdump"/></member>
   <member><xref linkend="app-postgres"/></member>
  </simplelist>
 </refsect1>
</refentry>
