Add functions pg_set_attribute_stats() and pg_clear_attribute_stats().

Enable manipulation of attribute statistics. Only superficial
validation is performed, so it's possible to add nonsense, and it's up
to the planner (or other users of statistics) to behave reasonably in
that case.

Bump catalog version.

Author: Corey Huinker
Discussion: https://postgr.es/m/CADkLM=eErgzn7ECDpwFcptJKOk9SxZEk5Pot4d94eVTZsvj3gw@mail.gmail.com

Author: jeff-davis

doc/src/sgml/func.sgml

@@ -30222,6 +30222,78 @@ DETAIL:  Make sure pg_wal_replay_wait() isn't called within a transaction with a
         </para>
        </entry>
       </row>
+
+      <row>
+       <entry role="func_table_entry">
+        <para role="func_signature">
+         <indexterm>
+          <primary>pg_set_attribute_stats</primary>
+         </indexterm>
+         <function>pg_set_attribute_stats</function> (
+         <parameter>relation</parameter> <type>regclass</type>,
+         <parameter>attname</parameter> <type>name</type>,
+         <parameter>inherited</parameter> <type>boolean</type>
+         <optional>, <parameter>null_frac</parameter> <type>real</type></optional>
+         <optional>, <parameter>avg_width</parameter> <type>integer</type></optional>
+         <optional>, <parameter>n_distinct</parameter> <type>real</type></optional>
+         <optional>, <parameter>most_common_vals</parameter> <type>text</type>, <parameter>most_common_freqs</parameter> <type>real[]</type> </optional>
+         <optional>, <parameter>histogram_bounds</parameter> <type>text</type> </optional>
+         <optional>, <parameter>correlation</parameter> <type>real</type> </optional>
+         <optional>, <parameter>most_common_elems</parameter> <type>text</type>, <parameter>most_common_elem_freqs</parameter> <type>real[]</type> </optional>
+         <optional>, <parameter>elem_count_histogram</parameter> <type>real[]</type> </optional>
+         <optional>, <parameter>range_length_histogram</parameter> <type>text</type> </optional>
+         <optional>, <parameter>range_empty_frac</parameter> <type>real</type> </optional>
+         <optional>, <parameter>range_bounds_histogram</parameter> <type>text</type> </optional> )
+         <returnvalue>void</returnvalue>
+        </para>
+        <para>
+         Creates or updates attribute-level statistics for the given relation
+         and attribute name to the specified values. The parameters correspond
+         to to attributes of the same name found in the <link
+         linkend="view-pg-stats"><structname>pg_stats</structname></link>
+         view.
+        </para>
+        <para>
+         Optional parameters default to <literal>NULL</literal>, which leave
+         the corresponding statistic unchanged.
+        </para>
+        <para>
+         Ordinarily, these statistics are collected automatically or updated
+         as a part of <xref linkend="sql-vacuum"/> or <xref
+         linkend="sql-analyze"/>, so it's not necessary to call this
+         function. However, it may be useful when testing the effects of
+         statistics on the planner to understand or anticipate plan changes.
+        </para>
+        <para>
+         The caller must have the <literal>MAINTAIN</literal> privilege on
+         the table or be the owner of the database.
+        </para>
+       </entry>
+      </row>
+
+      <row>
+       <entry role="func_table_entry">
+        <para role="func_signature">
+         <indexterm>
+          <primary>pg_clear_attribute_stats</primary>
+         </indexterm>
+         <function>pg_clear_attribute_stats</function> (
+         <parameter>relation</parameter> <type>regclass</type>,
+         <parameter>attname</parameter> <type>name</type>,
+         <parameter>inherited</parameter> <type>boolean</type> )
+         <returnvalue>boolean</returnvalue>
+        </para>
+        <para>
+         Clears table-level statistics for the given relation attribute, as
+         though the table was newly created.
+        </para>
+        <para>
+         The caller must have the <literal>MAINTAIN</literal> privilege on
+         the table or be the owner of the database.
+        </para>
+       </entry>
+      </row>
+
      </tbody>
     </tgroup>
    </table>

src/backend/catalog/system_functions.sql

@@ -649,6 +649,28 @@ LANGUAGE INTERNAL
 CALLED ON NULL INPUT VOLATILE
 AS 'pg_set_relation_stats';
 
+CREATE OR REPLACE FUNCTION
+  pg_set_attribute_stats(relation regclass,
+                         attname name,
+                         inherited bool,
+                         null_frac real DEFAULT NULL,
+                         avg_width integer DEFAULT NULL,
+                         n_distinct real DEFAULT NULL,
+                         most_common_vals text DEFAULT NULL,
+                         most_common_freqs real[] DEFAULT NULL,
+                         histogram_bounds text DEFAULT NULL,
+                         correlation real DEFAULT NULL,
+                         most_common_elems text DEFAULT NULL,
+                         most_common_elem_freqs real[] DEFAULT NULL,
+                         elem_count_histogram real[] DEFAULT NULL,
+                         range_length_histogram text DEFAULT NULL,
+                         range_empty_frac real DEFAULT NULL,
+                         range_bounds_histogram text DEFAULT NULL)
+RETURNS void
+LANGUAGE INTERNAL
+CALLED ON NULL INPUT VOLATILE
+AS 'pg_set_attribute_stats';
+
 --
 -- The default permissions for functions mean that anyone can execute them.
 -- A number of functions shouldn't be executable by just anyone, but rather

src/backend/statistics/Makefile

@@ -13,6 +13,7 @@ top_builddir = ../../..
 include $(top_builddir)/src/Makefile.global
 
 OBJS = \
+	attribute_stats.o \
 	dependencies.o \
 	extended_stats.o \
 	mcv.o \