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diff --git a/doc/src/sgml/html/runtime-config-compatible.html b/doc/src/sgml/html/runtime-config-compatible.html new file mode 100644 index 0000000..04639fe --- /dev/null +++ b/doc/src/sgml/html/runtime-config-compatible.html @@ -0,0 +1,143 @@ +<?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>20.13. 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 15.4 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</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</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>) + <a id="id-1.6.7.16.2.2.1.1.3" class="indexterm"></a> + </span></dt><dd><p> + This controls whether the array input parser recognizes + unquoted <code class="literal">NULL</code> as specifying a null array element. + By default, this is <code class="literal">on</code>, allowing array values containing + null values to be entered. However, <span class="productname">PostgreSQL</span> versions + before 8.2 did not support null values in arrays, and therefore would + treat <code class="literal">NULL</code> as specifying a normal array element with + the string value <span class="quote">“<span class="quote">NULL</span>”</span>. For backward compatibility with + applications that require the old behavior, this variable can be + turned <code class="literal">off</code>. + </p><p> + Note that it is possible to create array values containing null values + even when this variable is <code class="literal">off</code>. + </p></dd><dt id="GUC-BACKSLASH-QUOTE"><span class="term"><code class="varname">backslash_quote</code> (<code class="type">enum</code>) + <a id="id-1.6.7.16.2.2.2.1.3" class="indexterm"></a> + <a id="id-1.6.7.16.2.2.2.1.4" class="indexterm"></a> + </span></dt><dd><p> + This controls whether a quote mark can be represented by + <code class="literal">\'</code> in a string literal. The preferred, SQL-standard way + to represent a quote mark is by doubling it (<code class="literal">''</code>) but + <span class="productname">PostgreSQL</span> has historically also accepted + <code class="literal">\'</code>. However, use of <code class="literal">\'</code> creates security risks + because in some client character set encodings, there are multibyte + characters in which the last byte is numerically equivalent to ASCII + <code class="literal">\</code>. If client-side code does escaping incorrectly then an + SQL-injection attack is possible. This risk can be prevented by + making the server reject queries in which a quote mark appears to be + escaped by a backslash. + The allowed values of <code class="varname">backslash_quote</code> are + <code class="literal">on</code> (allow <code class="literal">\'</code> always), + <code class="literal">off</code> (reject always), and + <code class="literal">safe_encoding</code> (allow only if client encoding does not + allow ASCII <code class="literal">\</code> within a multibyte character). + <code class="literal">safe_encoding</code> is the default setting. + </p><p> + Note that in a standard-conforming string literal, <code class="literal">\</code> just + means <code class="literal">\</code> anyway. This parameter only affects the handling of + non-standard-conforming literals, including + escape string syntax (<code class="literal">E'...'</code>). + </p></dd><dt id="GUC-ESCAPE-STRING-WARNING"><span class="term"><code class="varname">escape_string_warning</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.16.2.2.3.1.3" class="indexterm"></a> + <a id="id-1.6.7.16.2.2.3.1.4" class="indexterm"></a> + </span></dt><dd><p> + When on, a warning is issued if a backslash (<code class="literal">\</code>) + appears in an ordinary string literal (<code class="literal">'...'</code> + syntax) and <code class="varname">standard_conforming_strings</code> is off. + The default is <code class="literal">on</code>. + </p><p> + Applications that wish to use backslash as escape should be + modified to use escape string syntax (<code class="literal">E'...'</code>), + because the default behavior of ordinary strings is now to treat + backslash as an ordinary character, per SQL standard. This variable + can be enabled to help locate code that needs to be changed. + </p></dd><dt id="GUC-LO-COMPAT-PRIVILEGES"><span class="term"><code class="varname">lo_compat_privileges</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.16.2.2.4.1.3" class="indexterm"></a> + </span></dt><dd><p> + In <span class="productname">PostgreSQL</span> releases prior to 9.0, large objects + did not have access privileges and were, therefore, always readable + and writable by all users. Setting this variable to <code class="literal">on</code> + disables the new privilege checks, for compatibility with prior + releases. The default is <code class="literal">off</code>. + Only superusers and users with the appropriate <code class="literal">SET</code> + privilege can change this setting. + </p><p> + Setting this variable does not disable all security checks related to + large objects — only those for which the default behavior has + changed in <span class="productname">PostgreSQL</span> 9.0. + </p></dd><dt id="GUC-QUOTE-ALL-IDENTIFIERS"><span class="term"><code class="varname">quote_all_identifiers</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.16.2.2.5.1.3" class="indexterm"></a> + </span></dt><dd><p> + When the database generates SQL, force all identifiers to be quoted, + even if they are not (currently) keywords. This will affect the + output of <code class="command">EXPLAIN</code> as well as the results of functions + like <code class="function">pg_get_viewdef</code>. See also the + <code class="option">--quote-all-identifiers</code> option of + <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>. + </p></dd><dt id="GUC-STANDARD-CONFORMING-STRINGS"><span class="term"><code class="varname">standard_conforming_strings</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.16.2.2.6.1.3" class="indexterm"></a> + <a id="id-1.6.7.16.2.2.6.1.4" class="indexterm"></a> + </span></dt><dd><p> + This controls whether ordinary string literals + (<code class="literal">'...'</code>) treat backslashes literally, as specified in + the SQL standard. + Beginning in <span class="productname">PostgreSQL</span> 9.1, the default is + <code class="literal">on</code> (prior releases defaulted to <code class="literal">off</code>). + Applications can check this + parameter to determine how string literals will be processed. + The presence of this parameter can also be taken as an indication + that the escape string syntax (<code class="literal">E'...'</code>) is supported. + 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>) + should be used if an application desires + backslashes to be treated as escape characters. + </p></dd><dt id="GUC-SYNCHRONIZE-SEQSCANS"><span class="term"><code class="varname">synchronize_seqscans</code> (<code class="type">boolean</code>) + <a id="id-1.6.7.16.2.2.7.1.3" class="indexterm"></a> + </span></dt><dd><p> + This allows sequential scans of large tables to synchronize with each + other, so that concurrent scans read the same block at about the + same time and hence share the I/O workload. When this is enabled, + a scan might start in the middle of the table and then <span class="quote">“<span class="quote">wrap + around</span>”</span> the end to cover all rows, so as to synchronize with the + activity of scans already in progress. This can result in + unpredictable changes in the row ordering returned by queries that + have no <code class="literal">ORDER BY</code> clause. Setting this parameter to + <code class="literal">off</code> ensures the pre-8.3 behavior in which a sequential + scan always starts from the beginning of the table. The default + is <code class="literal">on</code>. + </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</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>) + <a id="id-1.6.7.16.3.2.1.1.3" class="indexterm"></a> + <a id="id-1.6.7.16.3.2.1.1.4" class="indexterm"></a> + </span></dt><dd><p> + When on, expressions of the form <code class="literal"><em class="replaceable"><code>expr</code></em> = + NULL</code> (or <code class="literal">NULL = + <em class="replaceable"><code>expr</code></em></code>) are treated as + <code class="literal"><em class="replaceable"><code>expr</code></em> IS NULL</code>, that is, they + return true if <em class="replaceable"><code>expr</code></em> evaluates to the null value, + and false otherwise. The correct SQL-spec-compliant behavior of + <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> is to always + return null (unknown). Therefore this parameter defaults to + <code class="literal">off</code>. + </p><p> + However, filtered forms in <span class="productname">Microsoft + Access</span> generate queries that appear to use + <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> to test for + null values, so if you use that interface to access the database you + might want to turn this option on. Since expressions of the + form <code class="literal"><em class="replaceable"><code>expr</code></em> = NULL</code> always + return the null value (using the SQL standard interpretation), they are not + very useful and do not appear often in normal applications so + this option does little harm in practice. But new users are + frequently confused about the semantics of expressions + involving null values, so this option is off by default. + </p><p> + Note that this option only affects the exact form <code class="literal">= NULL</code>, + not other comparison operators or other expressions + that are computationally equivalent to some expression + involving the equals operator (such as <code class="literal">IN</code>). + Thus, this option is not a general fix for bad programming. + </p><p> + Refer to <a class="xref" href="functions-comparison.html" title="9.2. Comparison Functions and Operators">Section 9.2</a> for related information. + </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 15.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 20.14. Error Handling</td></tr></table></div></body></html>
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