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Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
2001-05-07 02:43:27 +02:00
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Merge documentation into one book. (Build with "make html".) Replace vague cross-references with real links.
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$Header: /cvsroot/pgsql/doc/src/sgml/ref/analyze.sgml,v 1.11 2003/03/25 16:15:39 petere Exp $
Use PostgreSQL consistantly throughout docs. Before, usage was split evenly between Postgres and PostgreSQL.
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PostgreSQL documentation
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
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<refentry id="SQL-ANALYZE">
<refmeta>
Augment the date/time examples in the User's Guide to reflect the newer capabilities of specifying time zones as intervals per SQL9x. Put refentrytitle contents on the same line as the tag. Otherwise, leading whitespace is propagated into the product, which (at least) messes up the ToC layout. Remove (some) docinfo tags containing dates. Best to omit if the dates are not accurate; maybe use CVS dates instead or leave them out.
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<refentrytitle id="sql-analyze-title">ANALYZE</refentrytitle>
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
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<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>
ANALYZE
</refname>
<refpurpose>
Put some kind of grammatical uniformity in the <refpurpose> lines.
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collect statistics about a database
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
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</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
<date>2001-05-04</date>
</refsynopsisdivinfo>
<synopsis>
ANALYZE [ VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> [ (<replaceable class="PARAMETER">column</replaceable> [, ...] ) ] ]
</synopsis>
<refsect2 id="R2-SQL-ANALYZE-1">
<refsect2info>
<date>2001-05-04</date>
</refsect2info>
<title>
Inputs
</title>
<para>
<variablelist>
<varlistentry>
<term>VERBOSE</term>
<listitem>
<para>
Enables display of progress messages.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">table</replaceable></term>
<listitem>
<para>
Update SQL-command reference pages for schema features.
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The name (possibly schema-qualified) of a specific table to
analyze. Defaults to all tables in the current database.
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
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</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">column</replaceable></term>
<listitem>
<para>
The name of a specific column to analyze. Defaults to all columns.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
<refsect2 id="R2-SQL-ANALYZE-2">
<refsect2info>
<date>2001-05-04</date>
</refsect2info>
<title>
Outputs
</title>
<para>
<variablelist>
<varlistentry>
<term><computeroutput>
<returnvalue>ANALYZE</returnvalue>
</computeroutput></term>
<listitem>
<para>
The command is complete.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
</refsynopsisdiv>
<refsect1 id="R1-SQL-ANALYZE-1">
<refsect1info>
<date>2001-05-04</date>
</refsect1info>
<title>
Description
</title>
<para>
<command>ANALYZE</command> collects statistics about the contents of
Use PostgreSQL consistantly throughout docs. Before, usage was split evenly between Postgres and PostgreSQL.
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<productname>PostgreSQL</productname> tables, and stores the results in
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
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the system table <literal>pg_statistic</literal>. Subsequently,
the query planner uses the statistics to help determine the most efficient
execution plans for queries.
</para>
<para>
With no parameter, <command>ANALYZE</command> examines every table in the
current database. With a parameter, <command>ANALYZE</command> examines
only that table. It is further possible to give a list of column names,
in which case only the statistics for those columns are updated.
</para>
<refsect2 id="R2-SQL-ANALYZE-3">
<refsect2info>
<date>2001-05-04</date>
</refsect2info>
<title>
Notes
</title>
<para>
It is a good idea to run <command>ANALYZE</command> periodically, or
just after making major changes in the contents of a table. Accurate
statistics will help the planner to choose the most appropriate query
plan, and thereby improve the speed of query processing. A common
Update various obsolete remarks about VACUUM.
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strategy is to run <xref linkend="sql-vacuum" endterm="sql-vacuum-title">
and <command>ANALYZE</command> once a day during a low-usage time of day.
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
2001-05-07 02:43:27 +02:00
</para>
<para>
Update various obsolete remarks about VACUUM.
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Unlike <command>VACUUM FULL</command>,
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
2001-05-07 02:43:27 +02:00
<command>ANALYZE</command> requires
only a read lock on the target table, so it can run in parallel with
other activity on the table.
</para>
<para>
For large tables, <command>ANALYZE</command> takes a random sample of the
table contents, rather than examining every row. This allows even very
large tables to be analyzed in a small amount of time. Note however
that the statistics are only approximate, and will change slightly each
time <command>ANALYZE</command> is run, even if the actual table contents
did not change. This may result in small changes in the planner's
estimated costs shown by <command>EXPLAIN</command>.
</para>
<para>
The collected statistics usually include a list of some of the most common
values in each column and a histogram showing the approximate data
distribution in each column. One or both of these may be omitted if
<command>ANALYZE</command> deems them uninteresting (for example, in
a unique-key column, there are no common values) or if the column
Spell-check and markup police
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data type does not support the appropriate operators. There is more
Merge documentation into one book. (Build with "make html".) Replace vague cross-references with real links.
2003-03-25 17:15:44 +01:00
information about the statistics in <xref linkend="maintenance">.
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
2001-05-07 02:43:27 +02:00
</para>
<para>
Instead of having a configure-time DEFAULT_ATTSTATTARGET, store -1 in attstattarget to indicate 'use the default'. The default is now a GUC variable default_statistics_target, and so may be changed on the fly. Along the way we gain the ability to have pg_dump dump the per-column statistics target when it's not the default. Patch by Neil Conway, with some kibitzing from Tom Lane.
2002-07-31 19:19:54 +02:00
The extent of analysis can be controlled by adjusting the
<literal>default_statistics_target</> parameter variable, or on a
column-by-column basis by setting the per-column
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
2001-05-07 02:43:27 +02:00
statistics target with <command>ALTER TABLE ALTER COLUMN SET
STATISTICS</command> (see
<xref linkend="sql-altertable" endterm="sql-altertable-title">). The
target value sets the maximum number of entries in the most-common-value
list and the maximum number of bins in the histogram. The default
target value is 10, but this can be adjusted up or down to trade off
accuracy of planner estimates against the time taken for
Instead of having a configure-time DEFAULT_ATTSTATTARGET, store -1 in attstattarget to indicate 'use the default'. The default is now a GUC variable default_statistics_target, and so may be changed on the fly. Along the way we gain the ability to have pg_dump dump the per-column statistics target when it's not the default. Patch by Neil Conway, with some kibitzing from Tom Lane.
2002-07-31 19:19:54 +02:00
<command>ANALYZE</command> and the amount of space occupied
in <literal>pg_statistic</literal>.
Rewrite of planner statistics-gathering code. ANALYZE is now available as a separate statement (though it can still be invoked as part of VACUUM, too). pg_statistic redesigned to be more flexible about what statistics are stored. ANALYZE now collects a list of several of the most common values, not just one, plus a histogram (not just the min and max values). Random sampling is used to make the process reasonably fast even on very large tables. The number of values and histogram bins collected is now user-settable via an ALTER TABLE command. There is more still to do; the new stats are not being used everywhere they could be in the planner. But the remaining changes for this project should be localized, and the behavior is already better than before. A not-very-related change is that sorting now makes use of btree comparison routines if it can find one, rather than invoking '<' twice.
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In particular, setting the statistics target to zero disables collection of
statistics for that column. It may be useful to do that for columns that
are never used as part of the WHERE, GROUP BY, or ORDER BY clauses of
queries, since the planner will have no use for statistics on such columns.
</para>
<para>
The largest statistics target among the columns being analyzed determines
the number of table rows sampled to prepare the statistics. Increasing
the target causes a proportional increase in the time and space needed
to do <command>ANALYZE</command>.
</para>
</refsect2>
</refsect1>
<refsect1 id="R1-SQL-ANALYZE-3">
<title>
Compatibility
</title>
<refsect2 id="R2-SQL-ANALYZE-4">
<refsect2info>
<date>2001-05-04</date>
</refsect2info>
<title>
SQL92
</title>
<para>
There is no <command>ANALYZE</command> statement in <acronym>SQL92</acronym>.
</para>
</refsect2>
</refsect1>
</refentry>
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