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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!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>20.15. 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="20.14. Error Handling" /><link rel="next" href="runtime-config-custom.html" title="20.16. 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">20.15. Preset Options</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="runtime-config-error-handling.html" title="20.14. Error Handling">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="runtime-config.html" title="Chapter 20. Server Configuration">Up</a></td><th width="60%" align="center">Chapter 20. Server Configuration</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="runtime-config-custom.html" title="20.16. 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">20.15. Preset Options</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-1.6.7.18.3.1.1.3" class="indexterm"></a>
</span></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="20.4. Resource Consumption">Section 20.4</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-1.6.7.18.3.2.1.3" class="indexterm"></a>
</span></dt><dd><p>
Reports whether data checksums are enabled for this cluster.
See <a class="xref" href="app-initdb.html#APP-INITDB-DATA-CHECKSUMS">data checksums</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-1.6.7.18.3.3.1.3" class="indexterm"></a>
</span></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="xref" href="app-initdb.html#APP-INITDB-ALLOW-GROUP-ACCESS">group access</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-1.6.7.18.3.4.1.3" class="indexterm"></a>
</span></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-INTEGER-DATETIMES"><span class="term"><code class="varname">integer_datetimes</code> (<code class="type">boolean</code>)
<a id="id-1.6.7.18.3.5.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.6.1.3" class="indexterm"></a>
</span></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="27.4. Hot Standby">Section 27.4</a> for more
information.
</p></dd><dt id="GUC-LC-COLLATE"><span class="term"><code class="varname">lc_collate</code> (<code class="type">string</code>)
<a id="id-1.6.7.18.3.7.1.3" class="indexterm"></a>
</span></dt><dd><p>
Reports the locale in which sorting of textual data is done.
See <a class="xref" href="locale.html" title="24.1. Locale Support">Section 24.1</a> for more information.
This value is determined when a database is created.
</p></dd><dt id="GUC-LC-CTYPE"><span class="term"><code class="varname">lc_ctype</code> (<code class="type">string</code>)
<a id="id-1.6.7.18.3.8.1.3" class="indexterm"></a>
</span></dt><dd><p>
Reports the locale that determines character classifications.
See <a class="xref" href="locale.html" title="24.1. Locale Support">Section 24.1</a> for more information.
This value is determined when a database is created.
Ordinarily this will be the same as <code class="varname">lc_collate</code>,
but for special applications it might be set differently.
</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-1.6.7.18.3.9.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.10.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.11.1.3" class="indexterm"></a>
</span></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-SEGMENT-SIZE"><span class="term"><code class="varname">segment_size</code> (<code class="type">integer</code>)
<a id="id-1.6.7.18.3.12.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.13.1.3" class="indexterm"></a>
<a id="id-1.6.7.18.3.13.1.4" class="indexterm"></a>
</span></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-1.6.7.18.3.14.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.15.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.16.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.17.1.3" class="indexterm"></a>
</span></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="19.4.5. Linux Huge Pages">Section 19.4.5</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-1.6.7.18.3.18.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.19.1.3" class="indexterm"></a>
</span></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-1.6.7.18.3.20.1.3" class="indexterm"></a>
</span></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="30.5. WAL Configuration">Section 30.5</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="20.14. Error Handling">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="runtime-config.html" title="Chapter 20. Server Configuration">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="runtime-config-custom.html" title="20.16. Customized Options">Next</a></td></tr><tr><td width="40%" align="left" valign="top">20.14. Error Handling </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 20.16. Customized Options</td></tr></table></div></body></html>
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