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Allow SET STATISTICS on expression indexes

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Index columns are referenced by ordinal number rather than name, e.g.
CREATE INDEX coord_idx ON measured (x, y, (z + t));
ALTER INDEX coord_idx ALTER COLUMN 3 SET STATISTICS 1000;

Incompatibility note for release notes:
\d+ for indexes now also displays Stats Target

Authors: Alexander Korotkov, with contribution by Adrien NAYRAT
Review: Adrien NAYRAT, Simon Riggs
Wordsmith: Simon Riggs
This commit is contained in:
Simon Riggs
2017-09-06 13:46:01 -07:00
parent e09db94c0a
commit 5b6d13eec7
13 changed files with 201 additions and 17 deletions
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39
doc/src/sgml/ref/alter_index.sgml
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@ -26,6 +26,8 @@ ALTER INDEX [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> SET
ALTER INDEX <replaceable class="PARAMETER">name</replaceable> DEPENDS ON EXTENSION <replaceable class="PARAMETER">extension_name</replaceable>
ALTER INDEX [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> SET ( <replaceable class="PARAMETER">storage_parameter</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] )
ALTER INDEX [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> RESET ( <replaceable class="PARAMETER">storage_parameter</replaceable> [, ... ] )
ALTER INDEX [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> ALTER [ COLUMN ] <replaceable class="PARAMETER">column_number</replaceable>
SET STATISTICS <replaceable class="PARAMETER">integer</replaceable>
ALTER INDEX ALL IN TABLESPACE <replaceable class="PARAMETER">name</replaceable> [ OWNED BY <replaceable class="PARAMETER">role_name</replaceable> [, ... ] ]
SET TABLESPACE <replaceable class="PARAMETER">new_tablespace</replaceable> [ NOWAIT ]
</synopsis>
@ -110,6 +112,25 @@ ALTER INDEX ALL IN TABLESPACE <replaceable class="PARAMETER">name</replaceable>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>ALTER [ COLUMN ] <replaceable class="PARAMETER">column_number</replaceable> SET STATISTICS <replaceable class="PARAMETER">integer</replaceable></literal></term>
<listitem>
<para>
This form sets the per-column statistics-gathering target for
subsequent <xref linkend="sql-analyze"> operations, though can
be used only on index columns that are defined as an expression.
Since expressions lack a unique name, we refer to them using the
ordinal number of the index column.
The target can be set in the range 0 to 10000; alternatively, set it
to -1 to revert to using the system default statistics
target (<xref linkend="guc-default-statistics-target">).
For more information on the use of statistics by the
<productname>PostgreSQL</productname> query planner, refer to
<xref linkend="planner-stats">.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
@ -130,6 +151,16 @@ ALTER INDEX ALL IN TABLESPACE <replaceable class="PARAMETER">name</replaceable>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">column_number</replaceable></term>
<listitem>
<para>
The ordinal number refers to the ordinal (left-to-right) position
of the index column.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">name</replaceable></term>
<listitem>
@ -235,6 +266,14 @@ ALTER INDEX distributors SET (fillfactor = 75);
REINDEX INDEX distributors;
</programlisting></para>
<para>
Set the statistics-gathering target for an expression index:
<programlisting>
CREATE INDEX coord_idx ON measured (x, y, (z + t));
ALTER INDEX coord_idx ALTER COLUMN 3 SET STATISTICS 1000;
</programlisting>
</para>
</refsect1>
<refsect1>