<!--
doc/src/sgml/ref/pg_amcheck.sgml
PostgreSQL documentation
-->

<refentry id="app-pgamcheck">
 <indexterm zone="app-pgamcheck">
  <primary>pg_amcheck</primary>
 </indexterm>

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

 <refnamediv>
  <refname>pg_amcheck</refname>
  <refpurpose>checks for corruption in one or more
  <productname>PostgreSQL</productname> databases</refpurpose>
 </refnamediv>

 <refsynopsisdiv>
  <cmdsynopsis>
   <command>pg_amcheck</command>
   <arg rep="repeat"><replaceable>option</replaceable></arg>
   <arg><replaceable>dbname</replaceable></arg>
  </cmdsynopsis>
 </refsynopsisdiv>

 <refsect1>
  <title>Description</title>

  <para>
   <application>pg_amcheck</application> supports running
   <xref linkend="amcheck"/>'s corruption checking functions against one or
   more databases, with options to select which schemas, tables and indexes to
   check, which kinds of checking to perform, and whether to perform the checks
   in parallel, and if so, the number of parallel connections to establish and
   use.
  </para>

  <para>
   Only ordinary and toast table relations, materialized views, sequences, and
   btree indexes are currently supported.  Other relation types are silently
   skipped.
  </para>

  <para>
   If <literal>dbname</literal> is specified, it should be the name of a
   single database to check, and no other database selection options should
   be present. Otherwise, if any database selection options are present,
   all matching databases will be checked. If no such options are present,
   the default database will be checked. Database selection options include
   <option>--all</option>, <option>--database</option> and
   <option>--exclude-database</option>. They also include
   <option>--relation</option>, <option>--exclude-relation</option>,
   <option>--table</option>, <option>--exclude-table</option>,
   <option>--index</option>, and <option>--exclude-index</option>,
   but only when such options are used with a three-part pattern
   (e.g. <option>mydb*.myschema*.myrel*</option>).  Finally, they include
   <option>--schema</option> and <option>--exclude-schema</option>
   when such options are used with a two-part pattern
   (e.g. <option>mydb*.myschema*</option>).
  </para>

  <para>
   <replaceable>dbname</replaceable> can also be a
   <link linkend="libpq-connstring">connection string</link>.
  </para>
 </refsect1>

 <refsect1>
  <title>Options</title>

  <para>
   The following command-line options control what is checked:

   <variablelist>
    <varlistentry>
     <term><option>-a</option></term>
     <term><option>--all</option></term>
       <listitem>
      <para>
       Check all databases, except for any excluded via
       <option>--exclude-database</option>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-d <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--database=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Check databases matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>,
       except for any excluded by <option>--exclude-database</option>.
       This option can be specified more than once.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-D <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--exclude-database=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Exclude databases matching the given
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>.
       This option can be specified more than once.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-i <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--index=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Check indexes matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>,
       unless they are otherwise excluded.
       This option can be specified more than once.
      </para>
      <para>
       This is similar to the <option>--relation</option> option, except that
       it applies only to indexes, not to other relation types.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-I <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--exclude-index=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Exclude indexes matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>.
       This option can be specified more than once.
      </para>
      <para>
       This is similar to the <option>--exclude-relation</option> option,
       except that it applies only to indexes, not other relation types.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-r <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--relation=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Check relations matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>,
       unless they are otherwise excluded.
       This option can be specified more than once.
      </para>
      <para>
       Patterns may be unqualified, e.g. <literal>myrel*</literal>, or they
       may be schema-qualified, e.g. <literal>myschema*.myrel*</literal> or
       database-qualified and schema-qualified, e.g.
       <literal>mydb*.myschema*.myrel*</literal>. A database-qualified
       pattern will add matching databases to the list of databases to be
       checked.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-R <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--exclude-relation=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Exclude relations matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>.
       This option can be specified more than once.
      </para>
      <para>
       As with <option>--relation</option>, the
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link> may be unqualified, schema-qualified,
       or database- and schema-qualified.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-s <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--schema=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Check tables and indexes in schemas matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>, unless they are otherwise excluded.
       This option can be specified more than once.
      </para>
      <para>
       To select only tables in schemas matching a particular pattern,
       consider using something like
       <literal>--table=SCHEMAPAT.* --no-dependent-indexes</literal>.
       To select only indexes, consider using something like
       <literal>--index=SCHEMAPAT.*</literal>.
      </para>
      <para>
       A schema pattern may be database-qualified. For example, you may
       write <literal>--schema=mydb*.myschema*</literal> to select
       schemas matching <literal>myschema*</literal> in databases matching
       <literal>mydb*</literal>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-S <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--exclude-schema=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Exclude tables and indexes in schemas matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>.
       This option can be specified more than once.
      </para>
      <para>
       As with <option>--schema</option>, the pattern may be
       database-qualified.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-t <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--table=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Check tables matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>,
       unless they are otherwise excluded.
       This option can be specified more than once.
      </para>
      <para>
       This is similar to the <option>--relation</option> option, except that
       it applies only to tables, materialized views, and sequences, not to
       indexes.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-T <replaceable class="parameter">pattern</replaceable></option></term>
     <term><option>--exclude-table=<replaceable class="parameter">pattern</replaceable></option></term>
     <listitem>
      <para>
       Exclude tables matching the specified
       <link linkend="app-psql-patterns"><replaceable class="parameter">pattern</replaceable></link>.
       This option can be specified more than once.
      </para>
      <para>
       This is similar to the <option>--exclude-relation</option> option,
       except that it applies only to tables, materialized views, and
       sequences, not to indexes.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--no-dependent-indexes</option></term>
     <listitem>
      <para>
       By default, if a table is checked, any btree indexes of that table
       will also be checked, even if they are not explicitly selected by
       an option such as <literal>--index</literal> or
       <literal>--relation</literal>. This option suppresses that behavior.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--no-dependent-toast</option></term>
     <listitem>
      <para>
       By default, if a table is checked, its toast table, if any, will also
       be checked, even if it is not explicitly selected by an option
       such as <literal>--table</literal> or <literal>--relation</literal>.
       This option suppresses that behavior.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--no-strict-names</option></term>
     <listitem>
      <para>
       By default, if an argument to <literal>--database</literal>,
       <literal>--table</literal>, <literal>--index</literal>,
       or <literal>--relation</literal> matches no objects, it is a fatal
       error. This option downgrades that error to a warning.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>

  <para>
   The following command-line options control checking of tables:

   <variablelist>
    <varlistentry>
     <term><option>--exclude-toast-pointers</option></term>
     <listitem>
      <para>
       By default, whenever a toast pointer is encountered in a table,
       a lookup is performed to ensure that it references apparently-valid
       entries in the toast table. These checks can be quite slow, and this
       option can be used to skip them.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--on-error-stop</option></term>
     <listitem>
      <para>
       After reporting all corruptions on the first page of a table where
       corruption is found, stop processing that table relation and move on
       to the next table or index.
      </para>
      <para>
       Note that index checking always stops after the first corrupt page.
       This option only has meaning relative to table relations.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--skip=<replaceable class="parameter">option</replaceable></option></term>
     <listitem>
      <para>
       If <literal>all-frozen</literal> is given, table corruption checks
       will skip over pages in all tables that are marked as all frozen.
      </para>
      <para>
       If <literal>all-visible</literal> is given, table corruption checks
       will skip over pages in all tables that are marked as all visible.
      </para>
      <para>
       By default, no pages are skipped.  This can be specified as
       <literal>none</literal>, but since this is the default, it need not be
       mentioned.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--startblock=<replaceable class="parameter">block</replaceable></option></term>
     <listitem>
      <para>
       Start checking at the specified block number. An error will occur if
       the table relation being checked has fewer than this number of blocks.
       This option does not apply to indexes, and is probably only useful
       when checking a single table relation. See <literal>--endblock</literal>
       for further caveats.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--endblock=<replaceable class="parameter">block</replaceable></option></term>
     <listitem>
      <para>
       End checking at the specified block number.  An error will occur if the
       table relation being checked has fewer than this number of blocks.
       This option does not apply to indexes, and is probably only useful when
       checking a single table relation. If both a regular table and a toast
       table are checked, this option will apply to both, but higher-numbered
       toast blocks may still be accessed while validating toast pointers,
       unless that is suppressed using
       <option>--exclude-toast-pointers</option>.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>

  <para>
   The following command-line options control checking of B-tree indexes:

   <variablelist>
    <varlistentry>
     <term><option>--checkunique</option></term>
     <listitem>
      <para>
       For each index with unique constraint checked, verify that no more than
       one among duplicate entries is visible in the index using <xref linkend="amcheck"/>'s
       <option>checkunique</option> option.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--heapallindexed</option></term>
     <listitem>
      <para>
       For each index checked, verify the presence of all heap tuples as index
       tuples in the index using <xref linkend="amcheck"/>'s
       <option>heapallindexed</option> option.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--parent-check</option></term>
     <listitem>
      <para>
       For each btree index checked, use <xref linkend="amcheck"/>'s
       <function>bt_index_parent_check</function> function, which performs
       additional checks of parent/child relationships during index checking.
      </para>
      <para>
       The default is to use <application>amcheck</application>'s
       <function>bt_index_check</function> function, but note that use of the
       <option>--rootdescend</option> option implicitly selects
       <function>bt_index_parent_check</function>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--rootdescend</option></term>
     <listitem>
      <para>
       For each index checked, re-find tuples on the leaf level by performing a
       new search from the root page for each tuple using
       <xref linkend="amcheck"/>'s <option>rootdescend</option> option.
      </para>
      <para>
       Use of this option implicitly also selects the
       <option>--parent-check</option> option.
      </para>
      <para>
       This form of verification was originally written to help in the
       development of btree index features.  It may be of limited use or even
       of no use in helping detect the kinds of corruption that occur in
       practice.  It may also cause corruption checking to take considerably
       longer and consume considerably more resources on the server.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>

  <warning>
   <para>
    The extra checks performed against B-tree indexes when the
    <option>--parent-check</option> option or the
    <option>--rootdescend</option> option is specified require
    relatively strong relation-level locks.  These checks are the only
    checks that will block concurrent data modification from
    <command>INSERT</command>, <command>UPDATE</command>, and
    <command>DELETE</command> commands.
   </para>
  </warning>

  <para>
   The following command-line options control the connection to the server:

   <variablelist>
    <varlistentry>
     <term><option>-h <replaceable class="parameter">hostname</replaceable></option></term>
     <term><option>--host=<replaceable class="parameter">hostname</replaceable></option></term>
     <listitem>
      <para>
       Specifies the host name of the machine on which the server is running.
       If the value begins with a slash, it is used as the directory for the
       Unix domain socket.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-p <replaceable class="parameter">port</replaceable></option></term>
     <term><option>--port=<replaceable class="parameter">port</replaceable></option></term>
     <listitem>
      <para>
       Specifies the TCP port or local Unix domain socket file extension on
       which the server is listening for connections.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-U</option></term>
     <term><option>--username=<replaceable class="parameter">username</replaceable></option></term>
     <listitem>
      <para>
       User name to connect as.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-w</option></term>
     <term><option>--no-password</option></term>
     <listitem>
      <para>
       Never issue a password prompt.  If the server requires password
       authentication and a password is not available by other means such as
       a <filename>.pgpass</filename> file, the connection attempt will fail.
       This option can be useful in batch jobs and scripts where no user is
       present to enter a password.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-W</option></term>
     <term><option>--password</option></term>
     <listitem>
      <para>
       Force <application>pg_amcheck</application> to prompt for a password
       before connecting to a database.
      </para>
      <para>
       This option is never essential, since
       <application>pg_amcheck</application> will automatically prompt for a
       password if the server demands password authentication.  However,
       <application>pg_amcheck</application> will waste a connection attempt
       finding out that the server wants a password.  In some cases it is
       worth typing <option>-W</option> to avoid the extra connection attempt.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--maintenance-db=<replaceable class="parameter">dbname</replaceable></option></term>
     <listitem>
      <para>
       Specifies a database or
       <link linkend="libpq-connstring">connection string</link> to be
       used to discover the list of databases to be checked. If neither
       <option>--all</option> nor any option including a database pattern is
       used, no such connection is required and this option does nothing.
       Otherwise, any connection string parameters other than
       the database name which are included in the value for this option
       will also be used when connecting to the databases
       being checked. If this option is omitted, the default is
       <literal>postgres</literal> or, if that fails,
       <literal>template1</literal>.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>

  <para>
   Other options are also available:

   <variablelist>
    <varlistentry>
     <term><option>-e</option></term>
     <term><option>--echo</option></term>
     <listitem>
      <para>
      Echo to stdout all SQL sent to the server.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-j <replaceable class="parameter">num</replaceable></option></term>
     <term><option>--jobs=<replaceable class="parameter">num</replaceable></option></term>
     <listitem>
      <para>
       Use <replaceable>num</replaceable> concurrent connections to the server,
       or one per object to be checked, whichever is less.
      </para>
      <para>
       The default is to use a single connection.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-P</option></term>
     <term><option>--progress</option></term>
     <listitem>
      <para>
       Show progress information. Progress information includes the number
       of relations for which checking has been completed, and the total
       size of those relations. It also includes the total number of relations
       that will eventually be checked, and the estimated size of those
       relations.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-v</option></term>
     <term><option>--verbose</option></term>
     <listitem>
      <para>
       Print more messages. In particular, this will print a message for
       each relation being checked, and will increase the level of detail
       shown for server errors.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-V</option></term>
     <term><option>--version</option></term>
     <listitem>
      <para>
       Print the <application>pg_amcheck</application> version and exit.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>--install-missing</option></term>
     <term><option>--install-missing=<replaceable class="parameter">schema</replaceable></option></term>
     <listitem>
      <para>
       Install any missing extensions that are required to check the
       database(s).  If not yet installed, each extension's objects will be
       installed into the given
       <replaceable class="parameter">schema</replaceable>, or if not specified
       into schema <literal>pg_catalog</literal>.
      </para>
      <para>
       At present, the only required extension is <xref linkend="amcheck"/>.
      </para>
     </listitem>
    </varlistentry>

    <varlistentry>
     <term><option>-?</option></term>
     <term><option>--help</option></term>
     <listitem>
      <para>
       Show help about <application>pg_amcheck</application> command line
       arguments, and exit.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1>
  <title>Environment</title>

  <para>
   <command>pg_amcheck</command>, like most other <productname>PostgreSQL</productname>
   utilities,
   also uses the environment variables supported by <application>libpq</application>
   (see <xref linkend="libpq-envars"/>).
  </para>

  <para>
   The environment variable <envar>PG_COLOR</envar> specifies whether to use
   color in diagnostic messages. Possible values are
   <literal>always</literal>, <literal>auto</literal> and
   <literal>never</literal>.
  </para>
 </refsect1>

 <refsect1>
  <title>Notes</title>

  <para>
   <application>pg_amcheck</application> is designed to work with
   <productname>PostgreSQL</productname> 14.0 and later.
  </para>
 </refsect1>

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

  <simplelist type="inline">
   <member><xref linkend="amcheck"/></member>
  </simplelist>
 </refsect1>
</refentry>