codekingpro/portable-devtools

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>20.13. Version and Platform Compatibility</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-locks.html" title="20.12. Lock Management" /><link rel="next" href="runtime-config-error-handling.html" title="20.14. Error Handling" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">20.13. Version and Platform Compatibility</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="runtime-config-locks.html" title="20.12. Lock Management">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-error-handling.html" title="20.14. Error Handling">Next</a></td></tr></table><hr /></div><div class="sect1" id="RUNTIME-CONFIG-COMPATIBLE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">20.13. Version and Platform Compatibility <a href="#RUNTIME-CONFIG-COMPATIBLE" class="id_link">#</a></h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="runtime-config-compatible.html#RUNTIME-CONFIG-COMPATIBLE-VERSION">20.13.1. Previous PostgreSQL Versions</a></span></dt><dt><span class="sect2"><a href="runtime-config-compatible.html#RUNTIME-CONFIG-COMPATIBLE-CLIENTS">20.13.2. Platform and Client Compatibility</a></span></dt></dl></div><div class="sect2" id="RUNTIME-CONFIG-COMPATIBLE-VERSION"><div class="titlepage"><div><div><h3 class="title">20.13.1. Previous PostgreSQL Versions <a href="#RUNTIME-CONFIG-COMPATIBLE-VERSION" class="id_link">#</a></h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt id="GUC-ARRAY-NULLS"><span class="term"><code class="varname">array_nulls</code> (<code class="type">boolean</code>)3      <a id="id-1.6.7.16.2.2.1.1.3" class="indexterm"></a>4      </span> <a href="#GUC-ARRAY-NULLS" class="id_link">#</a></dt><dd><p>5        This controls whether the array input parser recognizes6        unquoted <code class="literal">NULL</code> as specifying a null array element.7        By default, this is <code class="literal">on</code>, allowing array values containing8        null values to be entered.  However, <span class="productname">PostgreSQL</span> versions9        before 8.2 did not support null values in arrays, and therefore would10        treat <code class="literal">NULL</code> as specifying a normal array element with11        the string value <span class="quote">“<span class="quote">NULL</span>”</span>.  For backward compatibility with12        applications that require the old behavior, this variable can be13        turned <code class="literal">off</code>.14       </p><p>15        Note that it is possible to create array values containing null values16        even when this variable is <code class="literal">off</code>.17       </p></dd><dt id="GUC-BACKSLASH-QUOTE"><span class="term"><code class="varname">backslash_quote</code> (<code class="type">enum</code>)18      <a id="id-1.6.7.16.2.2.2.1.3" class="indexterm"></a>19      <a id="id-1.6.7.16.2.2.2.1.4" class="indexterm"></a>20      </span> <a href="#GUC-BACKSLASH-QUOTE" class="id_link">#</a></dt><dd><p>21        This controls whether a quote mark can be represented by22        <code class="literal">\'</code> in a string literal.  The preferred, SQL-standard way23        to represent a quote mark is by doubling it (<code class="literal">''</code>) but24        <span class="productname">PostgreSQL</span> has historically also accepted25        <code class="literal">\'</code>. However, use of <code class="literal">\'</code> creates security risks26        because in some client character set encodings, there are multibyte27        characters in which the last byte is numerically equivalent to ASCII28        <code class="literal">\</code>.  If client-side code does escaping incorrectly then an29        SQL-injection attack is possible.  This risk can be prevented by30        making the server reject queries in which a quote mark appears to be31        escaped by a backslash.32        The allowed values of <code class="varname">backslash_quote</code> are33        <code class="literal">on</code> (allow <code class="literal">\'</code> always),34        <code class="literal">off</code> (reject always), and35        <code class="literal">safe_encoding</code> (allow only if client encoding does not36        allow ASCII <code class="literal">\</code> within a multibyte character).37        <code class="literal">safe_encoding</code> is the default setting.38       </p><p>39        Note that in a standard-conforming string literal, <code class="literal">\</code> just40        means <code class="literal">\</code> anyway.  This parameter only affects the handling of41        non-standard-conforming literals, including42        escape string syntax (<code class="literal">E'...'</code>).43       </p></dd><dt id="GUC-ESCAPE-STRING-WARNING"><span class="term"><code class="varname">escape_string_warning</code> (<code class="type">boolean</code>)44      <a id="id-1.6.7.16.2.2.3.1.3" class="indexterm"></a>45      <a id="id-1.6.7.16.2.2.3.1.4" class="indexterm"></a>46      </span> <a href="#GUC-ESCAPE-STRING-WARNING" class="id_link">#</a></dt><dd><p>47        When on, a warning is issued if a backslash (<code class="literal">\</code>)48        appears in an ordinary string literal (<code class="literal">'...'</code>49        syntax) and <code class="varname">standard_conforming_strings</code> is off.50        The default is <code class="literal">on</code>.51       </p><p>52        Applications that wish to use backslash as escape should be53        modified to use escape string syntax (<code class="literal">E'...'</code>),54        because the default behavior of ordinary strings is now to treat55        backslash as an ordinary character, per SQL standard.  This variable56        can be enabled to help locate code that needs to be changed.57       </p></dd><dt id="GUC-LO-COMPAT-PRIVILEGES"><span class="term"><code class="varname">lo_compat_privileges</code> (<code class="type">boolean</code>)58      <a id="id-1.6.7.16.2.2.4.1.3" class="indexterm"></a>59      </span> <a href="#GUC-LO-COMPAT-PRIVILEGES" class="id_link">#</a></dt><dd><p>60        In <span class="productname">PostgreSQL</span> releases prior to 9.0, large objects61        did not have access privileges and were, therefore, always readable62        and writable by all users.  Setting this variable to <code class="literal">on</code>63        disables the new privilege checks, for compatibility with prior64        releases.  The default is <code class="literal">off</code>.65        Only superusers and users with the appropriate <code class="literal">SET</code>66        privilege can change this setting.67       </p><p>68        Setting this variable does not disable all security checks related to69        large objects — only those for which the default behavior has70        changed in <span class="productname">PostgreSQL</span> 9.0.71       </p></dd><dt id="GUC-QUOTE-ALL-IDENTIFIERS"><span class="term"><code class="varname">quote_all_identifiers</code> (<code class="type">boolean</code>)72      <a id="id-1.6.7.16.2.2.5.1.3" class="indexterm"></a>73      </span> <a href="#GUC-QUOTE-ALL-IDENTIFIERS" class="id_link">#</a></dt><dd><p>74        When the database generates SQL, force all identifiers to be quoted,75        even if they are not (currently) keywords.  This will affect the76        output of <code class="command">EXPLAIN</code> as well as the results of functions77        like <code class="function">pg_get_viewdef</code>.  See also the78        <code class="option">--quote-all-identifiers</code> option of79        <a class="xref" href="app-pgdump.html" title="pg_dump"><span class="refentrytitle"><span class="application">pg_dump</span></span></a> and <a class="xref" href="app-pg-dumpall.html" title="pg_dumpall"><span class="refentrytitle"><span class="application">pg_dumpall</span></span></a>.80       </p></dd><dt id="GUC-STANDARD-CONFORMING-STRINGS"><span class="term"><code class="varname">standard_conforming_strings</code> (<code class="type">boolean</code>)81      <a id="id-1.6.7.16.2.2.6.1.3" class="indexterm"></a>82      <a id="id-1.6.7.16.2.2.6.1.4" class="indexterm"></a>83      </span> <a href="#GUC-STANDARD-CONFORMING-STRINGS" class="id_link">#</a></dt><dd><p>84        This controls whether ordinary string literals85        (<code class="literal">'...'</code>) treat backslashes literally, as specified in86        the SQL standard.87        Beginning in <span class="productname">PostgreSQL</span> 9.1, the default is88        <code class="literal">on</code> (prior releases defaulted to <code class="literal">off</code>).89        Applications can check this90        parameter to determine how string literals will be processed.91        The presence of this parameter can also be taken as an indication92        that the escape string syntax (<code class="literal">E'...'</code>) is supported.93        Escape string syntax (<a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS-ESCAPE" title="4.1.2.2. String Constants with C-Style Escapes">Section 4.1.2.2</a>)94        should be used if an application desires95        backslashes to be treated as escape characters.96       </p></dd><dt id="GUC-SYNCHRONIZE-SEQSCANS"><span class="term"><code class="varname">synchronize_seqscans</code> (<code class="type">boolean</code>)97      <a id="id-1.6.7.16.2.2.7.1.3" class="indexterm"></a>98      </span> <a href="#GUC-SYNCHRONIZE-SEQSCANS" class="id_link">#</a></dt><dd><p>99        This allows sequential scans of large tables to synchronize with each100        other, so that concurrent scans read the same block at about the101        same time and hence share the I/O workload.  When this is enabled,102        a scan might start in the middle of the table and then <span class="quote">“<span class="quote">wrap103        around</span>”</span> the end to cover all rows, so as to synchronize with the104        activity of scans already in progress.  This can result in105        unpredictable changes in the row ordering returned by queries that106        have no <code class="literal">ORDER BY</code> clause.  Setting this parameter to107        <code class="literal">off</code> ensures the pre-8.3 behavior in which a sequential108        scan always starts from the beginning of the table.  The default109        is <code class="literal">on</code>.110       </p></dd></dl></div></div><div class="sect2" id="RUNTIME-CONFIG-COMPATIBLE-CLIENTS"><div class="titlepage"><div><div><h3 class="title">20.13.2. Platform and Client Compatibility <a href="#RUNTIME-CONFIG-COMPATIBLE-CLIENTS" class="id_link">#</a></h3></div></div></div><div class="variablelist"><dl class="variablelist"><dt id="GUC-TRANSFORM-NULL-EQUALS"><span class="term"><code class="varname">transform_null_equals</code> (<code class="type">boolean</code>)111      <a id="id-1.6.7.16.3.2.1.1.3" class="indexterm"></a>112      <a id="id-1.6.7.16.3.2.1.1.4" class="indexterm"></a>113      </span> <a href="#GUC-TRANSFORM-NULL-EQUALS" class="id_link">#</a></dt><dd><p>114        When on, expressions of the form <code class="literal"><em class="replaceable"><code>expr</code></em> =115        NULL</code> (or <code class="literal">NULL =116        <em class="replaceable"><code>expr</code></em></code>) are treated as117        <code class="literal"><em class="replaceable"><code>expr</code></em> IS NULL</code>, that is, they118        return true if <em class="replaceable"><code>expr</code></em> evaluates to the null value,119        and false otherwise. The correct SQL-spec-compliant behavior of120        <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> is to always121        return null (unknown). Therefore this parameter defaults to122        <code class="literal">off</code>.123       </p><p>124        However, filtered forms in <span class="productname">Microsoft125        Access</span> generate queries that appear to use126        <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> to test for127        null values, so if you use that interface to access the database you128        might want to turn this option on.  Since expressions of the129        form <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> always130        return the null value (using the SQL standard interpretation), they are not131        very useful and do not appear often in normal applications so132        this option does little harm in practice.  But new users are133        frequently confused about the semantics of expressions134        involving null values, so this option is off by default.135       </p><p>136        Note that this option only affects the exact form <code class="literal">= NULL</code>,137        not other comparison operators or other expressions138        that are computationally equivalent to some expression139        involving the equals operator (such as <code class="literal">IN</code>).140        Thus, this option is not a general fix for bad programming.141       </p><p>142        Refer to <a class="xref" href="functions-comparison.html" title="9.2. Comparison Functions and Operators">Section 9.2</a> for related information.143       </p></dd></dl></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="runtime-config-locks.html" title="20.12. Lock Management">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-error-handling.html" title="20.14. Error Handling">Next</a></td></tr><tr><td width="40%" align="left" valign="top">20.12. Lock Management </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 20.14. Error Handling</td></tr></table></div></body></html>