[Peter Eisentraut <peter.eisentraut@enterprisedb.com>]

After the discussion in [0] ff., I was looking around in pg_attribute 
and noticed that we could possibly save 4 bytes.  We could change both 
attstattarget and attinhcount from int4 to int2, which together with 
some reordering would save 4 bytes from the fixed portion.

attstattarget is already limited to 10000, so this wouldn't lose 
anything.  For attinhcount, I don't see any documented limits.  But it 
seems unlikely to me that someone would need more than 32k immediate 
inheritance parents on a column.  (Maybe an overflow check would be 
useful, though, to prevent shenanigans.)

The attached patch seems to work.  Thoughts?


[0]: 
https://www.postgresql.org/message-id/20230313204119.4mkepdvixcxrwpsc%40awork3.anarazel.de

Attachments:

0001-Save-a-few-bytes-in-pg_attribute.patch (text/plain, 7.3K) download
From 400f44d18875c40605147c8d81793c6dcc46f8a6 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 20 Mar 2023 09:51:20 +0100
Subject: [PATCH] Save a few bytes in pg_attribute

attstattarget and attinhcount can be converted to int16 (from int32).
---
 doc/src/sgml/catalogs.sgml         | 36 +++++++++++++++---------------
 src/backend/catalog/heap.c         |  4 ++--
 src/backend/catalog/index.c        |  2 +-
 src/include/catalog/pg_attribute.h | 20 ++++++++---------
 4 files changed, 31 insertions(+), 31 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index 746baf5053..ad5d15ec49 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -1164,23 +1164,6 @@ <title><structname>pg_attribute</structname> Columns</title>
       </para></entry>
      </row>
 
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>attstattarget</structfield> <type>int4</type>
-      </para>
-      <para>
-       <structfield>attstattarget</structfield> controls the level of detail
-       of statistics accumulated for this column by
-       <link linkend="sql-analyze"><command>ANALYZE</command></link>.
-       A zero value indicates that no statistics should be collected.
-       A negative value says to use the system default statistics target.
-       The exact meaning of positive values is data type-dependent.
-       For scalar data types, <structfield>attstattarget</structfield>
-       is both the target number of <quote>most common values</quote>
-       to collect, and the target number of histogram bins to create.
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>attlen</structfield> <type>int2</type>
@@ -1362,7 +1345,7 @@ <title><structname>pg_attribute</structname> Columns</title>
 
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>attinhcount</structfield> <type>int4</type>
+       <structfield>attinhcount</structfield> <type>int2</type>
       </para>
       <para>
        The number of direct ancestors this column has.  A column with a
@@ -1370,6 +1353,23 @@ <title><structname>pg_attribute</structname> Columns</title>
       </para></entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>attstattarget</structfield> <type>int2</type>
+      </para>
+      <para>
+       <structfield>attstattarget</structfield> controls the level of detail
+       of statistics accumulated for this column by
+       <link linkend="sql-analyze"><command>ANALYZE</command></link>.
+       A zero value indicates that no statistics should be collected.
+       A negative value says to use the system default statistics target.
+       The exact meaning of positive values is data type-dependent.
+       For scalar data types, <structfield>attstattarget</structfield>
+       is both the target number of <quote>most common values</quote>
+       to collect, and the target number of histogram bins to create.
+      </para></entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>attcollation</structfield> <type>oid</type>
diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index 4f006820b8..c67dfffa56 100644
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -732,7 +732,6 @@ InsertPgAttributeTuples(Relation pg_attribute_rel,
 
 		slot[slotCount]->tts_values[Anum_pg_attribute_attname - 1] = NameGetDatum(&attrs->attname);
 		slot[slotCount]->tts_values[Anum_pg_attribute_atttypid - 1] = ObjectIdGetDatum(attrs->atttypid);
-		slot[slotCount]->tts_values[Anum_pg_attribute_attstattarget - 1] = Int32GetDatum(attrs->attstattarget);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attlen - 1] = Int16GetDatum(attrs->attlen);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attnum - 1] = Int16GetDatum(attrs->attnum);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attndims - 1] = Int32GetDatum(attrs->attndims);
@@ -749,7 +748,8 @@ InsertPgAttributeTuples(Relation pg_attribute_rel,
 		slot[slotCount]->tts_values[Anum_pg_attribute_attgenerated - 1] = CharGetDatum(attrs->attgenerated);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attisdropped - 1] = BoolGetDatum(attrs->attisdropped);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attislocal - 1] = BoolGetDatum(attrs->attislocal);
-		slot[slotCount]->tts_values[Anum_pg_attribute_attinhcount - 1] = Int32GetDatum(attrs->attinhcount);
+		slot[slotCount]->tts_values[Anum_pg_attribute_attinhcount - 1] = Int16GetDatum(attrs->attinhcount);
+		slot[slotCount]->tts_values[Anum_pg_attribute_attstattarget - 1] = Int16GetDatum(attrs->attstattarget);
 		slot[slotCount]->tts_values[Anum_pg_attribute_attcollation - 1] = ObjectIdGetDatum(attrs->attcollation);
 		if (attoptions && attoptions[natts] != (Datum) 0)
 			slot[slotCount]->tts_values[Anum_pg_attribute_attoptions - 1] = attoptions[natts];
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 7777e7ec77..bccea1c749 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1812,7 +1812,7 @@ index_concurrently_swap(Oid newIndexId, Oid oldIndexId, const char *oldName)
 			memset(repl_repl, false, sizeof(repl_repl));
 
 			repl_repl[Anum_pg_attribute_attstattarget - 1] = true;
-			repl_val[Anum_pg_attribute_attstattarget - 1] = Int32GetDatum(attstattarget);
+			repl_val[Anum_pg_attribute_attstattarget - 1] = Int16GetDatum(attstattarget);
 
 			newTuple = heap_modify_tuple(attrTuple,
 										 RelationGetDescr(pg_attribute),
diff --git a/src/include/catalog/pg_attribute.h b/src/include/catalog/pg_attribute.h
index b561e17781..a0d6409036 100644
--- a/src/include/catalog/pg_attribute.h
+++ b/src/include/catalog/pg_attribute.h
@@ -52,15 +52,6 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
 	 */
 	Oid			atttypid BKI_LOOKUP_OPT(pg_type);
 
-	/*
-	 * attstattarget is the target number of statistics datapoints to collect
-	 * during VACUUM ANALYZE of this column.  A zero here indicates that we do
-	 * not wish to collect any stats about this column. A "-1" here indicates
-	 * that no value has been explicitly set for this column, so ANALYZE
-	 * should use the default setting.
-	 */
-	int32		attstattarget BKI_DEFAULT(-1);
-
 	/*
 	 * attlen is a copy of the typlen field from pg_type for this attribute.
 	 * See atttypid comments above.
@@ -165,7 +156,16 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
 	bool		attislocal BKI_DEFAULT(t);
 
 	/* Number of times inherited from direct parent relation(s) */
-	int32		attinhcount BKI_DEFAULT(0);
+	int16		attinhcount BKI_DEFAULT(0);
+
+	/*
+	 * attstattarget is the target number of statistics datapoints to collect
+	 * during VACUUM ANALYZE of this column.  A zero here indicates that we do
+	 * not wish to collect any stats about this column. A "-1" here indicates
+	 * that no value has been explicitly set for this column, so ANALYZE
+	 * should use the default setting.
+	 */
+	int16		attstattarget BKI_DEFAULT(-1);
 
 	/* attribute's collation, if any */
 	Oid			attcollation BKI_LOOKUP_OPT(pg_collation);

base-commit: 0b51d423e974557e821d890c0a3a49e419a19caa
-- 
2.39.2