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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!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 16.3 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 <a href="#RUNTIME-CONFIG-PRESET" class="id_link">#</a></h2></div></div></div><p>3 The following <span class="quote">“<span class="quote">parameters</span>”</span> are read-only.4 As such, they have been excluded from the sample5 <code class="filename">postgresql.conf</code> file. These options report6 various aspects of <span class="productname">PostgreSQL</span> behavior7 that might be of interest to certain applications, particularly8 administrative front-ends.9 Most of them are determined when <span class="productname">PostgreSQL</span>10 is compiled or when it is installed.11 </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>)12 <a id="id-1.6.7.18.3.1.1.3" class="indexterm"></a>13 </span> <a href="#GUC-BLOCK-SIZE" class="id_link">#</a></dt><dd><p>14 Reports the size of a disk block. It is determined by the value15 of <code class="literal">BLCKSZ</code> when building the server. The default16 value is 8192 bytes. The meaning of some configuration17 variables (such as <a class="xref" href="runtime-config-resource.html#GUC-SHARED-BUFFERS">shared_buffers</a>) is18 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.19 </p></dd><dt id="GUC-DATA-CHECKSUMS"><span class="term"><code class="varname">data_checksums</code> (<code class="type">boolean</code>)20 <a id="id-1.6.7.18.3.2.1.3" class="indexterm"></a>21 </span> <a href="#GUC-DATA-CHECKSUMS" class="id_link">#</a></dt><dd><p>22 Reports whether data checksums are enabled for this cluster.23 See <a class="xref" href="app-initdb.html#APP-INITDB-DATA-CHECKSUMS">data checksums</a> for more information.24 </p></dd><dt id="GUC-DATA-DIRECTORY-MODE"><span class="term"><code class="varname">data_directory_mode</code> (<code class="type">integer</code>)25 <a id="id-1.6.7.18.3.3.1.3" class="indexterm"></a>26 </span> <a href="#GUC-DATA-DIRECTORY-MODE" class="id_link">#</a></dt><dd><p>27 On Unix systems this parameter reports the permissions the data28 directory (defined by <a class="xref" href="runtime-config-file-locations.html#GUC-DATA-DIRECTORY">data_directory</a>)29 had at server startup.30 (On Microsoft Windows this parameter will always display31 <code class="literal">0700</code>.) See32 <a class="xref" href="app-initdb.html#APP-INITDB-ALLOW-GROUP-ACCESS">group access</a> for more information.33 </p></dd><dt id="GUC-DEBUG-ASSERTIONS"><span class="term"><code class="varname">debug_assertions</code> (<code class="type">boolean</code>)34 <a id="id-1.6.7.18.3.4.1.3" class="indexterm"></a>35 </span> <a href="#GUC-DEBUG-ASSERTIONS" class="id_link">#</a></dt><dd><p>36 Reports whether <span class="productname">PostgreSQL</span> has been built37 with assertions enabled. That is the case if the38 macro <code class="symbol">USE_ASSERT_CHECKING</code> is defined39 when <span class="productname">PostgreSQL</span> is built (accomplished40 e.g., by the <code class="command">configure</code> option41 <code class="option">--enable-cassert</code>). By42 default <span class="productname">PostgreSQL</span> is built without43 assertions.44 </p></dd><dt id="GUC-INTEGER-DATETIMES"><span class="term"><code class="varname">integer_datetimes</code> (<code class="type">boolean</code>)45 <a id="id-1.6.7.18.3.5.1.3" class="indexterm"></a>46 </span> <a href="#GUC-INTEGER-DATETIMES" class="id_link">#</a></dt><dd><p>47 Reports whether <span class="productname">PostgreSQL</span> was built with support for48 64-bit-integer dates and times. As of <span class="productname">PostgreSQL</span> 10,49 this is always <code class="literal">on</code>.50 </p></dd><dt id="GUC-IN-HOT-STANDBY"><span class="term"><code class="varname">in_hot_standby</code> (<code class="type">boolean</code>)51 <a id="id-1.6.7.18.3.6.1.3" class="indexterm"></a>52 </span> <a href="#GUC-IN-HOT-STANDBY" class="id_link">#</a></dt><dd><p>53 Reports whether the server is currently in hot standby mode. When54 this is <code class="literal">on</code>, all transactions are forced to be55 read-only. Within a session, this can change only if the server is56 promoted to be primary. See <a class="xref" href="hot-standby.html" title="27.4. Hot Standby">Section 27.4</a> for more57 information.58 </p></dd><dt id="GUC-MAX-FUNCTION-ARGS"><span class="term"><code class="varname">max_function_args</code> (<code class="type">integer</code>)59 <a id="id-1.6.7.18.3.7.1.3" class="indexterm"></a>60 </span> <a href="#GUC-MAX-FUNCTION-ARGS" class="id_link">#</a></dt><dd><p>61 Reports the maximum number of function arguments. It is determined by62 the value of <code class="literal">FUNC_MAX_ARGS</code> when building the server. The63 default value is 100 arguments.64 </p></dd><dt id="GUC-MAX-IDENTIFIER-LENGTH"><span class="term"><code class="varname">max_identifier_length</code> (<code class="type">integer</code>)65 <a id="id-1.6.7.18.3.8.1.3" class="indexterm"></a>66 </span> <a href="#GUC-MAX-IDENTIFIER-LENGTH" class="id_link">#</a></dt><dd><p>67 Reports the maximum identifier length. It is determined as one68 less than the value of <code class="literal">NAMEDATALEN</code> when building69 the server. The default value of <code class="literal">NAMEDATALEN</code> is70 64; therefore the default71 <code class="varname">max_identifier_length</code> is 63 bytes, which72 can be less than 63 characters when using multibyte encodings.73 </p></dd><dt id="GUC-MAX-INDEX-KEYS"><span class="term"><code class="varname">max_index_keys</code> (<code class="type">integer</code>)74 <a id="id-1.6.7.18.3.9.1.3" class="indexterm"></a>75 </span> <a href="#GUC-MAX-INDEX-KEYS" class="id_link">#</a></dt><dd><p>76 Reports the maximum number of index keys. It is determined by77 the value of <code class="literal">INDEX_MAX_KEYS</code> when building the server. The78 default value is 32 keys.79 </p></dd><dt id="GUC-SEGMENT-SIZE"><span class="term"><code class="varname">segment_size</code> (<code class="type">integer</code>)80 <a id="id-1.6.7.18.3.10.1.3" class="indexterm"></a>81 </span> <a href="#GUC-SEGMENT-SIZE" class="id_link">#</a></dt><dd><p>82 Reports the number of blocks (pages) that can be stored within a file83 segment. It is determined by the value of <code class="literal">RELSEG_SIZE</code>84 when building the server. The maximum size of a segment file in bytes85 is equal to <code class="varname">segment_size</code> multiplied by86 <code class="varname">block_size</code>; by default this is 1GB.87 </p></dd><dt id="GUC-SERVER-ENCODING"><span class="term"><code class="varname">server_encoding</code> (<code class="type">string</code>)88 <a id="id-1.6.7.18.3.11.1.3" class="indexterm"></a>89 <a id="id-1.6.7.18.3.11.1.4" class="indexterm"></a>90 </span> <a href="#GUC-SERVER-ENCODING" class="id_link">#</a></dt><dd><p>91 Reports the database encoding (character set).92 It is determined when the database is created. Ordinarily,93 clients need only be concerned with the value of <a class="xref" href="runtime-config-client.html#GUC-CLIENT-ENCODING">client_encoding</a>.94 </p></dd><dt id="GUC-SERVER-VERSION"><span class="term"><code class="varname">server_version</code> (<code class="type">string</code>)95 <a id="id-1.6.7.18.3.12.1.3" class="indexterm"></a>96 </span> <a href="#GUC-SERVER-VERSION" class="id_link">#</a></dt><dd><p>97 Reports the version number of the server. It is determined by the98 value of <code class="literal">PG_VERSION</code> when building the server.99 </p></dd><dt id="GUC-SERVER-VERSION-NUM"><span class="term"><code class="varname">server_version_num</code> (<code class="type">integer</code>)100 <a id="id-1.6.7.18.3.13.1.3" class="indexterm"></a>101 </span> <a href="#GUC-SERVER-VERSION-NUM" class="id_link">#</a></dt><dd><p>102 Reports the version number of the server as an integer. It is determined103 by the value of <code class="literal">PG_VERSION_NUM</code> when building the server.104 </p></dd><dt id="GUC-SHARED-MEMORY-SIZE"><span class="term"><code class="varname">shared_memory_size</code> (<code class="type">integer</code>)105 <a id="id-1.6.7.18.3.14.1.3" class="indexterm"></a>106 </span> <a href="#GUC-SHARED-MEMORY-SIZE" class="id_link">#</a></dt><dd><p>107 Reports the size of the main shared memory area, rounded up to the108 nearest megabyte.109 </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>)110 <a id="id-1.6.7.18.3.15.1.3" class="indexterm"></a>111 </span> <a href="#GUC-SHARED-MEMORY-SIZE-IN-HUGE-PAGES" class="id_link">#</a></dt><dd><p>112 Reports the number of huge pages that are needed for the main shared113 memory area based on the specified <a class="xref" href="runtime-config-resource.html#GUC-HUGE-PAGE-SIZE">huge_page_size</a>.114 If huge pages are not supported, this will be <code class="literal">-1</code>.115 </p><p>116 This setting is supported only on <span class="productname">Linux</span>. It117 is always set to <code class="literal">-1</code> on other platforms. For more118 details about using huge pages on <span class="productname">Linux</span>, see119 <a class="xref" href="kernel-resources.html#LINUX-HUGE-PAGES" title="19.4.5. Linux Huge Pages">Section 19.4.5</a>.120 </p></dd><dt id="GUC-SSL-LIBRARY"><span class="term"><code class="varname">ssl_library</code> (<code class="type">string</code>)121 <a id="id-1.6.7.18.3.16.1.3" class="indexterm"></a>122 </span> <a href="#GUC-SSL-LIBRARY" class="id_link">#</a></dt><dd><p>123 Reports the name of the SSL library that this124 <span class="productname">PostgreSQL</span> server was built with (even if125 SSL is not currently configured or in use on this instance), for126 example <code class="literal">OpenSSL</code>, or an empty string if none.127 </p></dd><dt id="GUC-WAL-BLOCK-SIZE"><span class="term"><code class="varname">wal_block_size</code> (<code class="type">integer</code>)128 <a id="id-1.6.7.18.3.17.1.3" class="indexterm"></a>129 </span> <a href="#GUC-WAL-BLOCK-SIZE" class="id_link">#</a></dt><dd><p>130 Reports the size of a WAL disk block. It is determined by the value131 of <code class="literal">XLOG_BLCKSZ</code> when building the server. The default value132 is 8192 bytes.133 </p></dd><dt id="GUC-WAL-SEGMENT-SIZE"><span class="term"><code class="varname">wal_segment_size</code> (<code class="type">integer</code>)134 <a id="id-1.6.7.18.3.18.1.3" class="indexterm"></a>135 </span> <a href="#GUC-WAL-SEGMENT-SIZE" class="id_link">#</a></dt><dd><p>136 Reports the size of write ahead log segments. The default value is137 16MB. See <a class="xref" href="wal-configuration.html" title="30.5. WAL Configuration">Section 30.5</a> for more information.138 </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. 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