0002-Display-length-and-bounds-histograms-in-p-20231125-2.patch

From 235b2f3de5fff7ae07b0499831435d7b536d6306 Mon Sep 17 00:00:00 2001
From: Alexander Korotkov <akorotkov@postgresql.org>
Date: Sat, 25 Nov 2023 00:38:37 +0200
Subject: [PATCH 2/2] Display length and bounds histograms in pg_stats

Values corresponding to STATISTIC_KIND_RANGE_LENGTH_HISTOGRAM and
STATISTIC_KIND_BOUNDS_HISTOGRAM were not exposed to pg_stats when these
slot kinds were introduced in 918eee0c49.

This commit adds the missing fields to pg_stats.

Catversion is bumped.

Discussion: https://postgr.es/m/flat/b67d8b57-9357-7e82-a2e7-f6ce6eaeec67@postgrespro.ru
Author: Egor Rogov, Soumyadeep Chakraborty
Reviewed-by: Tomas Vondra, Justin Pryzby, Jian He
---
 doc/src/sgml/system-views.sgml       | 39 ++++++++++++++++++++++++++++
 src/backend/catalog/system_views.sql | 23 +++++++++++++++-
 src/test/regress/expected/rules.out  | 26 ++++++++++++++++++-
 3 files changed, 86 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/system-views.sgml b/doc/src/sgml/system-views.sgml
index 7078491c4c0..0ef17456318 100644
--- a/doc/src/sgml/system-views.sgml
+++ b/doc/src/sgml/system-views.sgml
@@ -3799,6 +3799,45 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
        non-null elements.  (Null for scalar types.)
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>range_length_histogram</structfield> <type>anyarray</type>
+      </para>
+      <para>
+       A histogram of the lengths of non-empty and non-null range values of a
+       range type column. (Null for non-range types.)
+      </para>
+      <para>
+       This histogram is calculated using the <literal>subtype_diff</literal>
+       range function regardless of whether range bounds are inclusive.
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>range_empty_frac</structfield> <type>float4</type>
+      </para>
+      <para>
+       Fraction of column entries whose values are empty ranges.
+       (Null for non-range types.)
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>range_bounds_histogram</structfield> <type>anyarray</type>
+      </para>
+      <para>
+       A histogram of lower and upper bounds of non-empty and non-null range
+       values. (Null for non-range types.)
+      </para>
+      <para>
+       These two histograms are represented as a single array of ranges, whose
+       lower bounds represent the histogram of lower bounds, and upper bounds
+       represent the histogram of upper bounds.
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index b65f6b52490..11d18ed9dd6 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -243,7 +243,28 @@ CREATE VIEW pg_stats WITH (security_barrier) AS
             WHEN stakind3 = 5 THEN stanumbers3
             WHEN stakind4 = 5 THEN stanumbers4
             WHEN stakind5 = 5 THEN stanumbers5
-        END AS elem_count_histogram
+        END AS elem_count_histogram,
+        CASE
+            WHEN stakind1 = 6 THEN stavalues1
+            WHEN stakind2 = 6 THEN stavalues2
+            WHEN stakind3 = 6 THEN stavalues3
+            WHEN stakind4 = 6 THEN stavalues4
+            WHEN stakind5 = 6 THEN stavalues5
+        END AS range_length_histogram,
+        CASE
+            WHEN stakind1 = 6 THEN stanumbers1[1]
+            WHEN stakind2 = 6 THEN stanumbers2[1]
+            WHEN stakind3 = 6 THEN stanumbers3[1]
+            WHEN stakind4 = 6 THEN stanumbers4[1]
+            WHEN stakind5 = 6 THEN stanumbers5[1]
+        END AS range_empty_frac,
+        CASE
+            WHEN stakind1 = 7 THEN stavalues1
+            WHEN stakind2 = 7 THEN stavalues2
+            WHEN stakind3 = 7 THEN stavalues3
+            WHEN stakind4 = 7 THEN stavalues4
+            WHEN stakind5 = 7 THEN stavalues5
+            END AS range_bounds_histogram
     FROM pg_statistic s JOIN pg_class c ON (c.oid = s.starelid)
          JOIN pg_attribute a ON (c.oid = attrelid AND attnum = s.staattnum)
          LEFT JOIN pg_namespace n ON (n.oid = c.relnamespace)
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 1442c43d9c5..05070393b99 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2466,7 +2466,31 @@ pg_stats| SELECT n.nspname AS schemaname,
             WHEN (s.stakind4 = 5) THEN s.stanumbers4
             WHEN (s.stakind5 = 5) THEN s.stanumbers5
             ELSE NULL::real[]
-        END AS elem_count_histogram
+        END AS elem_count_histogram,
+        CASE
+            WHEN (s.stakind1 = 6) THEN s.stavalues1
+            WHEN (s.stakind2 = 6) THEN s.stavalues2
+            WHEN (s.stakind3 = 6) THEN s.stavalues3
+            WHEN (s.stakind4 = 6) THEN s.stavalues4
+            WHEN (s.stakind5 = 6) THEN s.stavalues5
+            ELSE NULL::anyarray
+        END AS range_length_histogram,
+        CASE
+            WHEN (s.stakind1 = 6) THEN s.stanumbers1[1]
+            WHEN (s.stakind2 = 6) THEN s.stanumbers2[1]
+            WHEN (s.stakind3 = 6) THEN s.stanumbers3[1]
+            WHEN (s.stakind4 = 6) THEN s.stanumbers4[1]
+            WHEN (s.stakind5 = 6) THEN s.stanumbers5[1]
+            ELSE NULL::real
+        END AS range_empty_frac,
+        CASE
+            WHEN (s.stakind1 = 7) THEN s.stavalues1
+            WHEN (s.stakind2 = 7) THEN s.stavalues2
+            WHEN (s.stakind3 = 7) THEN s.stavalues3
+            WHEN (s.stakind4 = 7) THEN s.stavalues4
+            WHEN (s.stakind5 = 7) THEN s.stavalues5
+            ELSE NULL::anyarray
+        END AS range_bounds_histogram
    FROM (((pg_statistic s
      JOIN pg_class c ON ((c.oid = s.starelid)))
      JOIN pg_attribute a ON (((c.oid = a.attrelid) AND (a.attnum = s.staattnum))))
-- 
2.39.3 (Apple Git-145)