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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>19.15. Preset Options</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="runtime-config-error-handling.html" title="19.14. Error Handling" /><link rel="next" href="runtime-config-custom.html" title="19.16. Customized Options" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">19.15. Preset Options</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="runtime-config-error-handling.html" title="19.14. Error Handling">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="runtime-config.html" title="Chapter 19. Server Configuration">Up</a></td><th width="60%" align="center">Chapter 19. Server Configuration</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 18.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="runtime-config-custom.html" title="19.16. Customized Options">Next</a></td></tr></table><hr /></div><div class="sect1" id="RUNTIME-CONFIG-PRESET"><div class="titlepage"><div><div><h2 class="title" style="clear: both">19.15. Preset Options <a href="#RUNTIME-CONFIG-PRESET" class="id_link">#</a></h2></div></div></div><p>
     The following <span class="quote">“<span class="quote">parameters</span>”</span> are read-only.
     As such, they have been excluded from the sample
     <code class="filename">postgresql.conf</code> file.  These options report
     various aspects of <span class="productname">PostgreSQL</span> behavior
     that might be of interest to certain applications, particularly
     administrative front-ends.
     Most of them are determined when <span class="productname">PostgreSQL</span>
     is compiled or when it is installed.
    </p><div class="variablelist"><dl class="variablelist"><dt id="GUC-BLOCK-SIZE"><span class="term"><code class="varname">block_size</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.1.1.3" class="indexterm"></a>
      </span> <a href="#GUC-BLOCK-SIZE" class="id_link">#</a></dt><dd><p>
        Reports the size of a disk block.  It is determined by the value
        of <code class="literal">BLCKSZ</code> when building the server. The default
        value is 8192 bytes.  The meaning of some configuration
        variables (such as <a class="xref" href="runtime-config-resource.html#GUC-SHARED-BUFFERS">shared_buffers</a>) is
        influenced by <code class="varname">block_size</code>. See <a class="xref" href="runtime-config-resource.html" title="19.4. Resource Consumption">Section 19.4</a> for information.
       </p></dd><dt id="GUC-DATA-CHECKSUMS"><span class="term"><code class="varname">data_checksums</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.18.3.2.1.3" class="indexterm"></a>
      </span> <a href="#GUC-DATA-CHECKSUMS" class="id_link">#</a></dt><dd><p>
        Reports whether data checksums are enabled for this cluster.
        See <a class="xref" href="app-initdb.html#APP-INITDB-DATA-CHECKSUMS"><code class="option">-k</code></a> for more information.
       </p></dd><dt id="GUC-DATA-DIRECTORY-MODE"><span class="term"><code class="varname">data_directory_mode</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.3.1.3" class="indexterm"></a>
      </span> <a href="#GUC-DATA-DIRECTORY-MODE" class="id_link">#</a></dt><dd><p>
        On Unix systems this parameter reports the permissions the data
        directory (defined by <a class="xref" href="runtime-config-file-locations.html#GUC-DATA-DIRECTORY">data_directory</a>)
        had at server startup.
        (On Microsoft Windows this parameter will always display
        <code class="literal">0700</code>.) See
        <a class="link" href="app-initdb.html#APP-INITDB-ALLOW-GROUP-ACCESS">the
        <span class="application">initdb</span> <code class="option">-g</code> option</a>
        for more information.
       </p></dd><dt id="GUC-DEBUG-ASSERTIONS"><span class="term"><code class="varname">debug_assertions</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.18.3.4.1.3" class="indexterm"></a>
      </span> <a href="#GUC-DEBUG-ASSERTIONS" class="id_link">#</a></dt><dd><p>
        Reports whether <span class="productname">PostgreSQL</span> has been built
        with assertions enabled. That is the case if the
        macro <code class="symbol">USE_ASSERT_CHECKING</code> is defined
        when <span class="productname">PostgreSQL</span> is built (accomplished
        e.g., by the <code class="command">configure</code> option
        <code class="option">--enable-cassert</code>). By
        default <span class="productname">PostgreSQL</span> is built without
        assertions.
       </p></dd><dt id="GUC-HUGE-PAGES-STATUS"><span class="term"><code class="varname">huge_pages_status</code> (<code class="type">enum</code>)
      <a id="id-1.6.6.18.3.5.1.3" class="indexterm"></a>
      </span> <a href="#GUC-HUGE-PAGES-STATUS" class="id_link">#</a></dt><dd><p>
        Reports the state of huge pages in the current instance:
        <code class="literal">on</code>, <code class="literal">off</code>, or
        <code class="literal">unknown</code> (if displayed with
        <code class="literal">postgres -C</code>).
        This parameter is useful to determine whether allocation of huge pages
        was successful under <code class="literal">huge_pages=try</code>.
        See <a class="xref" href="runtime-config-resource.html#GUC-HUGE-PAGES">huge_pages</a> for more information.
       </p></dd><dt id="GUC-INTEGER-DATETIMES"><span class="term"><code class="varname">integer_datetimes</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.18.3.6.1.3" class="indexterm"></a>
      </span> <a href="#GUC-INTEGER-DATETIMES" class="id_link">#</a></dt><dd><p>
        Reports whether <span class="productname">PostgreSQL</span> was built with support for
        64-bit-integer dates and times.  As of <span class="productname">PostgreSQL</span> 10,
        this is always <code class="literal">on</code>.
       </p></dd><dt id="GUC-IN-HOT-STANDBY"><span class="term"><code class="varname">in_hot_standby</code> (<code class="type">boolean</code>)
      <a id="id-1.6.6.18.3.7.1.3" class="indexterm"></a>
      </span> <a href="#GUC-IN-HOT-STANDBY" class="id_link">#</a></dt><dd><p>
        Reports whether the server is currently in hot standby mode.  When
        this is <code class="literal">on</code>, all transactions are forced to be
        read-only.  Within a session, this can change only if the server is
        promoted to be primary.  See <a class="xref" href="hot-standby.html" title="26.4. Hot Standby">Section 26.4</a> for more
        information.
       </p></dd><dt id="GUC-MAX-FUNCTION-ARGS"><span class="term"><code class="varname">max_function_args</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.8.1.3" class="indexterm"></a>
      </span> <a href="#GUC-MAX-FUNCTION-ARGS" class="id_link">#</a></dt><dd><p>
        Reports the maximum number of function arguments. It is determined by
        the value of <code class="literal">FUNC_MAX_ARGS</code> when building the server. The
        default value is 100 arguments.
       </p></dd><dt id="GUC-MAX-IDENTIFIER-LENGTH"><span class="term"><code class="varname">max_identifier_length</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.9.1.3" class="indexterm"></a>
      </span> <a href="#GUC-MAX-IDENTIFIER-LENGTH" class="id_link">#</a></dt><dd><p>
        Reports the maximum identifier length. It is determined as one
        less than the value of <code class="literal">NAMEDATALEN</code> when building
        the server. The default value of <code class="literal">NAMEDATALEN</code> is
        64; therefore the default
        <code class="varname">max_identifier_length</code> is 63 bytes, which
        can be less than 63 characters when using multibyte encodings.
       </p></dd><dt id="GUC-MAX-INDEX-KEYS"><span class="term"><code class="varname">max_index_keys</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.10.1.3" class="indexterm"></a>
      </span> <a href="#GUC-MAX-INDEX-KEYS" class="id_link">#</a></dt><dd><p>
        Reports the maximum number of index keys. It is determined by
        the value of <code class="literal">INDEX_MAX_KEYS</code> when building the server. The
        default value is 32 keys.
       </p></dd><dt id="GUC-NUM-OS-SEMAPHORES"><span class="term"><code class="varname">num_os_semaphores</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.11.1.3" class="indexterm"></a>
      </span> <a href="#GUC-NUM-OS-SEMAPHORES" class="id_link">#</a></dt><dd><p>
        Reports the number of semaphores that are needed for the server based
        on the configured number of allowed connections
        (<a class="xref" href="runtime-config-connection.html#GUC-MAX-CONNECTIONS">max_connections</a>), allowed autovacuum worker
        processes (<a class="xref" href="runtime-config-vacuum.html#GUC-AUTOVACUUM-MAX-WORKERS">autovacuum_max_workers</a>), allowed WAL
        sender processes (<a class="xref" href="runtime-config-replication.html#GUC-MAX-WAL-SENDERS">max_wal_senders</a>), allowed
        background processes (<a class="xref" href="runtime-config-resource.html#GUC-MAX-WORKER-PROCESSES">max_worker_processes</a>), etc.
       </p></dd><dt id="GUC-SEGMENT-SIZE"><span class="term"><code class="varname">segment_size</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.12.1.3" class="indexterm"></a>
      </span> <a href="#GUC-SEGMENT-SIZE" class="id_link">#</a></dt><dd><p>
        Reports the number of blocks (pages) that can be stored within a file
        segment.  It is determined by the value of <code class="literal">RELSEG_SIZE</code>
        when building the server.  The maximum size of a segment file in bytes
        is equal to <code class="varname">segment_size</code> multiplied by
        <code class="varname">block_size</code>; by default this is 1GB.
       </p></dd><dt id="GUC-SERVER-ENCODING"><span class="term"><code class="varname">server_encoding</code> (<code class="type">string</code>)
      <a id="id-1.6.6.18.3.13.1.3" class="indexterm"></a>
      <a id="id-1.6.6.18.3.13.1.4" class="indexterm"></a>
      </span> <a href="#GUC-SERVER-ENCODING" class="id_link">#</a></dt><dd><p>
        Reports the database encoding (character set).
        It is determined when the database is created.  Ordinarily,
        clients need only be concerned with the value of <a class="xref" href="runtime-config-client.html#GUC-CLIENT-ENCODING">client_encoding</a>.
       </p></dd><dt id="GUC-SERVER-VERSION"><span class="term"><code class="varname">server_version</code> (<code class="type">string</code>)
      <a id="id-1.6.6.18.3.14.1.3" class="indexterm"></a>
      </span> <a href="#GUC-SERVER-VERSION" class="id_link">#</a></dt><dd><p>
        Reports the version number of the server. It is determined by the
        value of <code class="literal">PG_VERSION</code> when building the server.
       </p></dd><dt id="GUC-SERVER-VERSION-NUM"><span class="term"><code class="varname">server_version_num</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.15.1.3" class="indexterm"></a>
      </span> <a href="#GUC-SERVER-VERSION-NUM" class="id_link">#</a></dt><dd><p>
        Reports the version number of the server as an integer. It is determined
        by the value of <code class="literal">PG_VERSION_NUM</code> when building the server.
       </p></dd><dt id="GUC-SHARED-MEMORY-SIZE"><span class="term"><code class="varname">shared_memory_size</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.16.1.3" class="indexterm"></a>
      </span> <a href="#GUC-SHARED-MEMORY-SIZE" class="id_link">#</a></dt><dd><p>
        Reports the size of the main shared memory area, rounded up to the
        nearest megabyte.
       </p></dd><dt id="GUC-SHARED-MEMORY-SIZE-IN-HUGE-PAGES"><span class="term"><code class="varname">shared_memory_size_in_huge_pages</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.17.1.3" class="indexterm"></a>
      </span> <a href="#GUC-SHARED-MEMORY-SIZE-IN-HUGE-PAGES" class="id_link">#</a></dt><dd><p>
        Reports the number of huge pages that are needed for the main shared
        memory area based on the specified <a class="xref" href="runtime-config-resource.html#GUC-HUGE-PAGE-SIZE">huge_page_size</a>.
        If huge pages are not supported, this will be <code class="literal">-1</code>.
       </p><p>
        This setting is supported only on <span class="productname">Linux</span>.  It
        is always set to <code class="literal">-1</code> on other platforms.  For more
        details about using huge pages on <span class="productname">Linux</span>, see
        <a class="xref" href="kernel-resources.html#LINUX-HUGE-PAGES" title="18.4.5. Linux Huge Pages">Section 18.4.5</a>.
       </p></dd><dt id="GUC-SSL-LIBRARY"><span class="term"><code class="varname">ssl_library</code> (<code class="type">string</code>)
      <a id="id-1.6.6.18.3.18.1.3" class="indexterm"></a>
      </span> <a href="#GUC-SSL-LIBRARY" class="id_link">#</a></dt><dd><p>
        Reports the name of the SSL library that this
        <span class="productname">PostgreSQL</span> server was built with (even if
        SSL is not currently configured or in use on this instance), for
        example <code class="literal">OpenSSL</code>, or an empty string if none.
       </p></dd><dt id="GUC-WAL-BLOCK-SIZE"><span class="term"><code class="varname">wal_block_size</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.19.1.3" class="indexterm"></a>
      </span> <a href="#GUC-WAL-BLOCK-SIZE" class="id_link">#</a></dt><dd><p>
        Reports the size of a WAL disk block.  It is determined by the value
        of <code class="literal">XLOG_BLCKSZ</code> when building the server. The default value
        is 8192 bytes.
       </p></dd><dt id="GUC-WAL-SEGMENT-SIZE"><span class="term"><code class="varname">wal_segment_size</code> (<code class="type">integer</code>)
      <a id="id-1.6.6.18.3.20.1.3" class="indexterm"></a>
      </span> <a href="#GUC-WAL-SEGMENT-SIZE" class="id_link">#</a></dt><dd><p>
        Reports the size of write ahead log segments.  The default value is
        16MB. See <a class="xref" href="wal-configuration.html" title="28.5. WAL Configuration">Section 28.5</a> for more information.
       </p></dd></dl></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="runtime-config-error-handling.html" title="19.14. Error Handling">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="runtime-config.html" title="Chapter 19. Server Configuration">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="runtime-config-custom.html" title="19.16. Customized Options">Next</a></td></tr><tr><td width="40%" align="left" valign="top">19.14. Error Handling </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 18.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 19.16. Customized Options</td></tr></table></div></body></html>