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accesses versus sequential accesses, a (very crude) estimate of the effects of caching on random page accesses, and cost to evaluate WHERE- clause expressions. Export critical parameters for this model as SET variables. Also, create SET variables for the planner's enable flags (enable_seqscan, enable_indexscan, etc) so that these can be controlled more conveniently than via PGOPTIONS. Planner now estimates both startup cost (cost before retrieving first tuple) and total cost of each path, so it can optimize queries with LIMIT on a reasonable basis by interpolating between these costs. Same facility is a win for EXISTS(...) subqueries and some other cases. Redesign pathkey representation to achieve a major speedup in planning (I saw as much as 5X on a 10-way join); also minor changes in planner to reduce memory consumption by recycling discarded Path nodes and not constructing unnecessary lists. Minor cleanups to display more-plausible costs in some cases in EXPLAIN output. Initdb forced by change in interface to index cost estimation functions.
195 lines
4.1 KiB
Plaintext
195 lines
4.1 KiB
Plaintext
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/show.sgml,v 1.8 2000/02/15 20:49:07 tgl Exp $
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Postgres documentation
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-->
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<refentry id="SQL-SHOW">
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<refmeta>
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<refentrytitle id="SQL-SHOW-TITLE">
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SHOW
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</refentrytitle>
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>
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SHOW
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</refname>
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<refpurpose>
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Shows run-time parameters for session
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</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<refsynopsisdivinfo>
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<date>1999-07-20</date>
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</refsynopsisdivinfo>
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<synopsis>
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SHOW <replaceable class="PARAMETER">keyword</replaceable>
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</synopsis>
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<refsect2 id="R2-SQL-SHOW-1">
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<refsect2info>
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<date>1998-09-24</date>
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</refsect2info>
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<title>
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Inputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term><replaceable class="PARAMETER">keyword</replaceable></term>
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<listitem>
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<para>
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Refer to <command>SET</command> for more information on available
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arguments.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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<refsect2 id="R2-SQL-SHOW-2">
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<refsect2info>
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<date>1998-09-24</date>
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</refsect2info>
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<title>
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Outputs
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</title>
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<para>
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<variablelist>
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<varlistentry>
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<term><computeroutput>
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NOTICE: <replaceable class="PARAMETER">variable</replaceable> is <replaceable>value</replaceable>
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SHOW VARIABLE
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</computeroutput></term>
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<listitem>
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<para>
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Message returned if successful.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><computeroutput>
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NOTICE: Unrecognized variable <replaceable>value</replaceable>
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</computeroutput></term>
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<listitem>
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<para>
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Message returned if <returnvalue>value</returnvalue> does not exist.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><computeroutput>
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NOTICE: Time zone is unknown
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SHOW VARIABLE
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</computeroutput></term>
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<listitem>
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<para>
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If the <envar>TZ</envar> or <envar>PGTZ</envar> environment
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variable is not set.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect2>
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</refsynopsisdiv>
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<refsect1 id="R1-SQL-SHOW-1">
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<refsect1info>
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<date>1998-09-24</date>
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</refsect1info>
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<title>
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Description
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</title>
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<para>
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<command>SHOW</command> will display the current setting of a
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run-time parameter during a session.
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</para>
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<para>
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These variables can be set using the <command>SET</command> statement,
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and
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can be restored to the default values using the <command>RESET</command>
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statement.
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Parameters and values are case-insensitive.
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</para>
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<refsect2 id="R2-SQL-SHOW-3">
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<refsect2info>
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<date>1998-09-24</date>
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</refsect2info>
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<title>
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Notes
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</title>
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<para>
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<command>SHOW</command> is a <productname>Postgres</productname>
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language extension.
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</para>
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<para>
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Refer to <command>SET</command>/<command>RESET</command>
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to set/reset variable values.
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</para>
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</refsect2>
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</refsect1>
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<refsect1 id="R1-SQL-SHOW-2">
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<title>
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Usage
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</title>
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<para>
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Show the current <literal>DateStyle</literal> setting:
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<programlisting>
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SHOW DateStyle;
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NOTICE:DateStyle is Postgres with US (NonEuropean) conventions
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</programlisting>
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</para>
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<para>
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Show the current genetic optimizer (<literal>geqo</literal>) setting:
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<programlisting>
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SHOW GEQO;
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NOTICE:GEQO is ON
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</programlisting>
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</para>
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</refsect1>
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<refsect1 id="R1-SQL-SHOW-3">
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<title>
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Compatibility
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</title>
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<refsect2 id="R2-SQL-SHOW-4">
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<refsect2info>
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<date>1998-09-24</date>
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</refsect2info>
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<title>
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SQL92
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</title>
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<para>
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There is no <command>SHOW</command> defined in <acronym>SQL92</acronym>.
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</para>
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</refsect2>
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</refsect1>
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</refentry>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:nil
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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sgml-parent-document:nil
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sgml-default-dtd-file:"../reference.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:"/usr/lib/sgml/catalog"
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sgml-local-ecat-files:nil
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End:
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-->
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