Subject: Make attstattarget nullable

From: Peter Eisentraut <[email-masked]>
Date: Tue, 5 Dec 2023 13:52:36 +0100

In [0] it was discussed that we could make attstattarget a nullable 
column, instead of always storing an explicit -1 default value for most 
columns.  This patch implements this.

This changes the pg_attribute field attstattarget into a nullable field 
in the variable-length part of the row.  If no value is set by the user 
for attstattarget, it is now null instead of previously -1.  This saves 
space in pg_attribute and tuple descriptors for most practical 
scenarios.  (ATTRIBUTE_FIXED_PART_SIZE is reduced from 108 to 104.) 
Also, null is the semantically more correct value.

The ANALYZE code internally continues to represent the default 
statistics target by -1, so that that code can avoid having to deal with 
null values.  But that is now contained to ANALYZE code.  The DDL code 
deals with attstattarget possibly null.

For system columns, the field is now always null but the effective value 
0 (don't analyze) is assumed.

To set a column's statistics target to the default value, the new 
command form ALTER TABLE ... SET STATISTICS DEFAULT can be used.  (SET 
STATISTICS -1 still works.)

[0]: 
https://www.postgresql.org/message-id/flat/d07ffc2b-e0e8-77f7-38fb-be921dff71af%40enterprisedb.com
From 174d51a66c80a3284ad97b347a286a7b65a2a440 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <[email-masked]>
Date: Tue, 5 Dec 2023 13:43:30 +0100
Subject: [PATCH v1] Make attstattarget nullable

This changes the pg_attribute field attstattarget into a nullable
field in the variable-length part of the row.  If no value is set by
the user for attstattarget, it is now null instead of previously -1.
This saves space in pg_attribute and tuple descriptors for most
practical scenarios.  (ATTRIBUTE_FIXED_PART_SIZE is reduced from 108
to 104.)  Also, null is the semantically more correct value.

The ANALYZE code internally continues to represent the default
statistics target by -1, so that that code can avoid having to deal
with null values.  But that is now contained to ANALYZE code.  The DDL
code deals with attstattarget possibly null.

For system columns, the field is now always null but the effective
value 0 (don't analyze) is assumed.

To set a column's statistics target to the default value, the new
command form ALTER TABLE ... SET STATISTICS DEFAULT can be used.  (SET
STATISTICS -1 still works.)

TODO: catversion
---
 doc/src/sgml/ref/alter_table.sgml          |  4 +-
 src/backend/access/common/tupdesc.c        |  4 --
 src/backend/bootstrap/bootstrap.c          |  1 -
 src/backend/catalog/genbki.pl              |  1 -
 src/backend/catalog/heap.c                 | 25 ++++++------
 src/backend/catalog/index.c                | 23 ++++++++---
 src/backend/commands/analyze.c             |  7 +++-
 src/backend/commands/tablecmds.c           | 44 +++++++++++++++++-----
 src/backend/parser/gram.y                  | 18 ++++++---
 src/backend/utils/cache/lsyscache.c        | 17 +++++++--
 src/bin/pg_dump/pg_dump.c                  |  7 +++-
 src/include/catalog/pg_attribute.h         | 16 ++++----
 src/include/commands/vacuum.h              |  2 +-
 src/test/regress/expected/create_index.out |  4 +-
 14 files changed, 113 insertions(+), 60 deletions(-)

diff --git a/doc/src/sgml/ref/alter_table.sgml b/doc/src/sgml/ref/alter_table.sgml
index e1d207bc60..9d637157eb 100644
--- a/doc/src/sgml/ref/alter_table.sgml
+++ b/doc/src/sgml/ref/alter_table.sgml
@@ -50,7 +50,7 @@
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( <replaceable>sequence_options</replaceable> ) ]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> { SET GENERATED { ALWAYS | BY DEFAULT } | SET <replaceable>sequence_option</replaceable> | RESTART [ [ WITH ] <replaceable class="parameter">restart</replaceable> ] } [...]
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> DROP IDENTITY [ IF EXISTS ]
-    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET STATISTICS <replaceable class="parameter">integer</replaceable>
+    ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET STATISTICS { <replaceable class="parameter">integer</replaceable> | DEFAULT }
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET ( <replaceable class="parameter">attribute_option</replaceable> = <replaceable class="parameter">value</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> RESET ( <replaceable class="parameter">attribute_option</replaceable> [, ... ] )
     ALTER [ COLUMN ] <replaceable class="parameter">column_name</replaceable> SET STORAGE { PLAIN | EXTERNAL | EXTENDED | MAIN | DEFAULT }
@@ -317,7 +317,7 @@ <title>Description</title>
       sets the per-column statistics-gathering target for subsequent
       <link linkend="sql-analyze"><command>ANALYZE</command></link> operations.
       The target can be set in the range 0 to 10000; alternatively, set it
-      to -1 to revert to using the system default statistics
+      to <literal>DEFAULT</literal> 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
diff --git a/src/backend/access/common/tupdesc.c b/src/backend/access/common/tupdesc.c
index 8826519e5e..054ccff1e2 100644
--- a/src/backend/access/common/tupdesc.c
+++ b/src/backend/access/common/tupdesc.c
@@ -453,8 +453,6 @@ equalTupleDescs(TupleDesc tupdesc1, TupleDesc tupdesc2)
 			return false;
 		if (attr1->atttypid != attr2->atttypid)
 			return false;
-		if (attr1->attstattarget != attr2->attstattarget)
-			return false;
 		if (attr1->attlen != attr2->attlen)
 			return false;
 		if (attr1->attndims != attr2->attndims)
@@ -639,7 +637,6 @@ TupleDescInitEntry(TupleDesc desc,
 	else if (attributeName != NameStr(att->attname))
 		namestrcpy(&(att->attname), attributeName);
 
-	att->attstattarget = -1;
 	att->attcacheoff = -1;
 	att->atttypmod = typmod;
 
@@ -702,7 +699,6 @@ TupleDescInitBuiltinEntry(TupleDesc desc,
 	Assert(attributeName != NULL);
 	namestrcpy(&(att->attname), attributeName);
 
-	att->attstattarget = -1;
 	att->attcacheoff = -1;
 	att->atttypmod = typmod;
 
diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index e01dca9b7c..c7546da51e 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -552,7 +552,6 @@ DefineAttr(char *name, char *type, int attnum, int nullness)
 	if (OidIsValid(attrtypes[attnum]->attcollation))
 		attrtypes[attnum]->attcollation = C_COLLATION_OID;
 
-	attrtypes[attnum]->attstattarget = -1;
 	attrtypes[attnum]->attcacheoff = -1;
 	attrtypes[attnum]->atttypmod = -1;
 	attrtypes[attnum]->attislocal = true;
diff --git a/src/backend/catalog/genbki.pl b/src/backend/catalog/genbki.pl
index 380bc23c82..13cd2fee14 100644
--- a/src/backend/catalog/genbki.pl
+++ b/src/backend/catalog/genbki.pl
@@ -840,7 +840,6 @@ sub gen_pg_attribute
 				my %row;
 				$row{attnum} = $attnum;
 				$row{attrelid} = $table->{relation_oid};
-				$row{attstattarget} = '0';
 
 				morph_row_for_pgattr(\%row, $schema, $attr, 1);
 				print_bki_insert(\%row, $schema);
diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index 7224d96695..6e08d9b496 100644
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -749,14 +749,16 @@ InsertPgAttributeTuples(Relation pg_attribute_rel,
 		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] = 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];
 		else
 			slot[slotCount]->tts_isnull[Anum_pg_attribute_attoptions - 1] = true;
 
-		/* start out with empty permissions and empty options */
+		/*
+		 * The remaining fields are not set for new columns.
+		 */
+		slot[slotCount]->tts_isnull[Anum_pg_attribute_attstattarget - 1] = true;
 		slot[slotCount]->tts_isnull[Anum_pg_attribute_attacl - 1] = true;
 		slot[slotCount]->tts_isnull[Anum_pg_attribute_attfdwoptions - 1] = true;
 		slot[slotCount]->tts_isnull[Anum_pg_attribute_attmissingval - 1] = true;
@@ -818,9 +820,6 @@ AddNewAttributeTuples(Oid new_rel_oid,
 
 	indstate = CatalogOpenIndexes(rel);
 
-	/* set stats detail level to a sane default */
-	for (int i = 0; i < natts; i++)
-		tupdesc->attrs[i].attstattarget = -1;
 	InsertPgAttributeTuples(rel, tupdesc, new_rel_oid, NULL, indstate);
 
 	/* add dependencies on their datatypes and collations */
@@ -1647,6 +1646,9 @@ RemoveAttributeById(Oid relid, AttrNumber attnum)
 	HeapTuple	tuple;
 	Form_pg_attribute attStruct;
 	char		newattname[NAMEDATALEN];
+	Datum		valuesAtt[Natts_pg_attribute] = {0};
+	bool		nullsAtt[Natts_pg_attribute] = {0};
+	bool		replacesAtt[Natts_pg_attribute] = {0};
 
 	/*
 	 * Grab an exclusive lock on the target table, which we will NOT release
@@ -1683,7 +1685,8 @@ RemoveAttributeById(Oid relid, AttrNumber attnum)
 	attStruct->attnotnull = false;
 
 	/* We don't want to keep stats for it anymore */
-	attStruct->attstattarget = 0;
+	nullsAtt[Anum_pg_attribute_attstattarget - 1] = true;
+	replacesAtt[Anum_pg_attribute_attstattarget - 1] = true;
 
 	/* Unset this so no one tries to look up the generation expression */
 	attStruct->attgenerated = '\0';
@@ -1698,10 +1701,6 @@ RemoveAttributeById(Oid relid, AttrNumber attnum)
 	/* clear the missing value if any */
 	if (attStruct->atthasmissing)
 	{
-		Datum		valuesAtt[Natts_pg_attribute] = {0};
-		bool		nullsAtt[Natts_pg_attribute] = {0};
-		bool		replacesAtt[Natts_pg_attribute] = {0};
-
 		/* update the tuple - set atthasmissing and attmissingval */
 		valuesAtt[Anum_pg_attribute_atthasmissing - 1] =
 			BoolGetDatum(false);
@@ -1709,11 +1708,11 @@ RemoveAttributeById(Oid relid, AttrNumber attnum)
 		valuesAtt[Anum_pg_attribute_attmissingval - 1] = (Datum) 0;
 		nullsAtt[Anum_pg_attribute_attmissingval - 1] = true;
 		replacesAtt[Anum_pg_attribute_attmissingval - 1] = true;
-
-		tuple = heap_modify_tuple(tuple, RelationGetDescr(attr_rel),
-								  valuesAtt, nullsAtt, replacesAtt);
 	}
 
+	tuple = heap_modify_tuple(tuple, RelationGetDescr(attr_rel),
+							  valuesAtt, nullsAtt, replacesAtt);
+
 	CatalogTupleUpdate(attr_rel, &tuple->t_self, tuple);
 
 	/*
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index b8c7945322..60fa4e5c4a 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -325,7 +325,6 @@ ConstructTupleDescriptor(Relation heapRelation,
 
 		MemSet(to, 0, ATTRIBUTE_FIXED_PART_SIZE);
 		to->attnum = i + 1;
-		to->attstattarget = -1;
 		to->attcacheoff = -1;
 		to->attislocal = true;
 		to->attcollation = (i < numkeyatts) ? collationIds[i] : InvalidOid;
@@ -1780,31 +1779,45 @@ index_concurrently_swap(Oid newIndexId, Oid oldIndexId, const char *oldName)
 		while (HeapTupleIsValid((attrTuple = systable_getnext(scan))))
 		{
 			Form_pg_attribute att = (Form_pg_attribute) GETSTRUCT(attrTuple);
+			HeapTuple	tp;
+			Datum		dat1,
+						dat2;
+			bool		isnull1,
+						isnull2;
 			Datum		repl_val[Natts_pg_attribute];
 			bool		repl_null[Natts_pg_attribute];
 			bool		repl_repl[Natts_pg_attribute];
-			int			attstattarget;
 			HeapTuple	newTuple;
 
 			/* Ignore dropped columns */
 			if (att->attisdropped)
 				continue;
 
+			dat1 = heap_getattr(attrTuple, Anum_pg_attribute_attstattarget, RelationGetDescr(pg_attribute), &isnull1);
+
 			/*
 			 * Get attstattarget from the old index and refresh the new value.
 			 */
-			attstattarget = get_attstattarget(oldIndexId, att->attnum);
+			tp = SearchSysCache2(ATTNUM, ObjectIdGetDatum(oldIndexId), Int16GetDatum(att->attnum));
+			if (!HeapTupleIsValid(tp))
+				elog(ERROR, "cache lookup failed for attribute %d of relation %u",
+					 att->attnum, oldIndexId);
+			dat2 = SysCacheGetAttr(ATTNUM, tp, Anum_pg_attribute_attstattarget, &isnull2);
+			ReleaseSysCache(tp);
 
 			/* no need for a refresh if both match */
-			if (attstattarget == att->attstattarget)
+			if ((isnull1 && isnull2) || (!isnull1 && !isnull2 && DatumGetInt16(dat1) == DatumGetInt16(dat2)))
 				continue;
 
 			memset(repl_val, 0, sizeof(repl_val));
 			memset(repl_null, false, sizeof(repl_null));
 			memset(repl_repl, false, sizeof(repl_repl));
 
+			if (isnull2)
+				repl_null[Anum_pg_attribute_attstattarget - 1] = true;
+			else
+				repl_val[Anum_pg_attribute_attstattarget - 1] = dat2;
 			repl_repl[Anum_pg_attribute_attstattarget - 1] = true;
-			repl_val[Anum_pg_attribute_attstattarget - 1] = Int16GetDatum(attstattarget);
 
 			newTuple = heap_modify_tuple(attrTuple,
 										 RelationGetDescr(pg_attribute),
diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index e264ffdcf2..116ac23fa4 100644
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -1001,6 +1001,7 @@ static VacAttrStats *
 examine_attribute(Relation onerel, int attnum, Node *index_expr)
 {
 	Form_pg_attribute attr = TupleDescAttr(onerel->rd_att, attnum - 1);
+	int			attstattarget;
 	HeapTuple	typtuple;
 	VacAttrStats *stats;
 	int			i;
@@ -1010,15 +1011,17 @@ examine_attribute(Relation onerel, int attnum, Node *index_expr)
 	if (attr->attisdropped)
 		return NULL;
 
+	attstattarget = get_attstattarget(RelationGetRelid(onerel), attnum);
+
 	/* Don't analyze column if user has specified not to */
-	if (attr->attstattarget == 0)
+	if (attstattarget == 0)
 		return NULL;
 
 	/*
 	 * Create the VacAttrStats struct.
 	 */
 	stats = (VacAttrStats *) palloc0(sizeof(VacAttrStats));
-	stats->attstattarget = attr->attstattarget;
+	stats->attstattarget = attstattarget;
 
 	/*
 	 * When analyzing an expression index, believe the expression tree's type
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 6b0a20010e..77bb17c479 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -7124,7 +7124,6 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	attribute.attrelid = myrelid;
 	namestrcpy(&(attribute.attname), colDef->colname);
 	attribute.atttypid = typeOid;
-	attribute.attstattarget = -1;
 	attribute.attlen = tform->typlen;
 	attribute.attnum = newattnum;
 	if (list_length(colDef->typeName->arrayBounds) > PG_INT16_MAX)
@@ -8453,10 +8452,14 @@ ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newVa
 {
 	int			newtarget;
 	Relation	attrelation;
-	HeapTuple	tuple;
+	HeapTuple	tuple,
+				newtuple;
 	Form_pg_attribute attrtuple;
 	AttrNumber	attnum;
 	ObjectAddress address;
+	Datum		repl_val[Natts_pg_attribute];
+	bool		repl_null[Natts_pg_attribute];
+	bool		repl_repl[Natts_pg_attribute];
 
 	/*
 	 * We allow referencing columns by numbers only for indexes, since table
@@ -8469,8 +8472,18 @@ ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newVa
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("cannot refer to non-index column by number")));
 
-	Assert(IsA(newValue, Integer));
-	newtarget = intVal(newValue);
+	if (newValue)
+	{
+		Assert(IsA(newValue, Integer));
+		newtarget = intVal(newValue);
+	}
+	else
+	{
+		/*
+		 * -1 was used in previous versions to represent the default setting
+		 */
+		newtarget = -1;
+	}
 
 	/*
 	 * Limit target to a sane range
@@ -8495,7 +8508,7 @@ ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newVa
 
 	if (colName)
 	{
-		tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);
+		tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);
 
 		if (!HeapTupleIsValid(tuple))
 			ereport(ERROR,
@@ -8505,7 +8518,7 @@ ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newVa
 	}
 	else
 	{
-		tuple = SearchSysCacheCopyAttNum(RelationGetRelid(rel), colNum);
+		tuple = SearchSysCacheAttNum(RelationGetRelid(rel), colNum);
 
 		if (!HeapTupleIsValid(tuple))
 			ereport(ERROR,
@@ -8539,16 +8552,27 @@ ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newVa
 					 errhint("Alter statistics on table column instead.")));
 	}
 
-	attrtuple->attstattarget = newtarget;
-
-	CatalogTupleUpdate(attrelation, &tuple->t_self, tuple);
+	/* Build new tuple. */
+	memset(repl_null, false, sizeof(repl_null));
+	memset(repl_repl, false, sizeof(repl_repl));
+	if (newtarget != -1)
+		repl_val[Anum_pg_attribute_attstattarget - 1] = newtarget;
+	else
+		repl_null[Anum_pg_attribute_attstattarget - 1] = true;
+	repl_repl[Anum_pg_attribute_attstattarget - 1] = true;
+	newtuple = heap_modify_tuple(tuple, RelationGetDescr(attrelation),
+								 repl_val, repl_null, repl_repl);
+	CatalogTupleUpdate(attrelation, &tuple->t_self, newtuple);
 
 	InvokeObjectPostAlterHook(RelationRelationId,
 							  RelationGetRelid(rel),
 							  attrtuple->attnum);
 	ObjectAddressSubSet(address, RelationRelationId,
 						RelationGetRelid(rel), attnum);
-	heap_freetuple(tuple);
+
+	heap_freetuple(newtuple);
+
+	ReleaseSysCache(tuple);
 
 	table_close(attrelation, RowExclusiveLock);
 
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index d631ac89a9..b86bc0c298 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -337,6 +337,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 %type <list>	alter_table_cmds alter_type_cmds
 %type <list>    alter_identity_column_option_list
 %type <defelt>  alter_identity_column_option
+%type <node>	set_statistics_value
 
 %type <list>	createdb_opt_list createdb_opt_items copy_opt_list
 				transaction_mode_list
@@ -2436,18 +2437,18 @@ alter_table_cmd:
 					n->missing_ok = true;
 					$$ = (Node *) n;
 				}
-			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET STATISTICS <SignedIconst> */
-			| ALTER opt_column ColId SET STATISTICS SignedIconst
+			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET STATISTICS */
+			| ALTER opt_column ColId SET STATISTICS set_statistics_value
 				{
 					AlterTableCmd *n = makeNode(AlterTableCmd);
 
 					n->subtype = AT_SetStatistics;
 					n->name = $3;
-					n->def = (Node *) makeInteger($6);
+					n->def = $6;
 					$$ = (Node *) n;
 				}
-			/* ALTER TABLE <name> ALTER [COLUMN] <colnum> SET STATISTICS <SignedIconst> */
-			| ALTER opt_column Iconst SET STATISTICS SignedIconst
+			/* ALTER TABLE <name> ALTER [COLUMN] <colnum> SET STATISTICS */
+			| ALTER opt_column Iconst SET STATISTICS set_statistics_value
 				{
 					AlterTableCmd *n = makeNode(AlterTableCmd);
 
@@ -2459,7 +2460,7 @@ alter_table_cmd:
 
 					n->subtype = AT_SetStatistics;
 					n->num = (int16) $3;
-					n->def = (Node *) makeInteger($6);
+					n->def = $6;
 					$$ = (Node *) n;
 				}
 			/* ALTER TABLE <name> ALTER [COLUMN] <colname> SET ( column_parameter = value [, ... ] ) */
@@ -3060,6 +3061,11 @@ alter_identity_column_option:
 				}
 		;
 
+set_statistics_value:
+			SignedIconst					{ $$ = (Node *) makeInteger($1); }
+			| DEFAULT						{ $$ = NULL; }
+		;
+
 PartitionBoundSpec:
 			/* a HASH partition */
 			FOR VALUES WITH '(' hash_partbound ')'
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index fc6d267e44..238d25d81d 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -878,23 +878,34 @@ get_attnum(Oid relid, const char *attname)
  *		Given the relation id and the attribute number,
  *		return the "attstattarget" field from the attribute relation.
  *
+ *		Returns	-1 if attstattarget is null.
+ *
+ *		Always returns 0 for system columns.
+ *
  *		Errors if not found.
  */
 int
 get_attstattarget(Oid relid, AttrNumber attnum)
 {
 	HeapTuple	tp;
-	Form_pg_attribute att_tup;
+	Datum		dat;
+	bool		isnull;
 	int			result;
 
+	if (attnum < 0)
+		return 0;
+
 	tp = SearchSysCache2(ATTNUM,
 						 ObjectIdGetDatum(relid),
 						 Int16GetDatum(attnum));
 	if (!HeapTupleIsValid(tp))
 		elog(ERROR, "cache lookup failed for attribute %d of relation %u",
 			 attnum, relid);
-	att_tup = (Form_pg_attribute) GETSTRUCT(tp);
-	result = att_tup->attstattarget;
+	dat = SysCacheGetAttr(ATTNUM, tp, Anum_pg_attribute_attstattarget, &isnull);
+	if (isnull)
+		result = -1;
+	else
+		result = DatumGetInt16(dat);
 	ReleaseSysCache(tp);
 	return result;
 }
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 8c0b5486b9..bc3651a73a 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -8682,7 +8682,10 @@ getTableAttrs(Archive *fout, TableInfo *tblinfo, int numTables)
 						 tbinfo->dobj.name);
 			tbinfo->attnames[j] = pg_strdup(PQgetvalue(res, r, i_attname));
 			tbinfo->atttypnames[j] = pg_strdup(PQgetvalue(res, r, i_atttypname));
-			tbinfo->attstattarget[j] = atoi(PQgetvalue(res, r, i_attstattarget));
+			if (PQgetisnull(res, r, i_attstattarget))
+				tbinfo->attstattarget[j] = -1;
+			else
+				tbinfo->attstattarget[j] = atoi(PQgetvalue(res, r, i_attstattarget));
 			tbinfo->attstorage[j] = *(PQgetvalue(res, r, i_attstorage));
 			tbinfo->typstorage[j] = *(PQgetvalue(res, r, i_typstorage));
 			tbinfo->attidentity[j] = *(PQgetvalue(res, r, i_attidentity));
@@ -16261,7 +16264,7 @@ dumpTableSchema(Archive *fout, const TableInfo *tbinfo)
 			/*
 			 * Dump per-column statistics information. We only issue an ALTER
 			 * TABLE statement if the attstattarget entry for this column is
-			 * non-negative (i.e. it's not the default value)
+			 * not the default value.
 			 */
 			if (tbinfo->attstattarget[j] >= 0)
 				appendPQExpBuffer(q, "ALTER %sTABLE ONLY %s ALTER COLUMN %s SET STATISTICS %d;\n",
diff --git a/src/include/catalog/pg_attribute.h b/src/include/catalog/pg_attribute.h
index 672a5a16ff..337a2d5bf9 100644
--- a/src/include/catalog/pg_attribute.h
+++ b/src/include/catalog/pg_attribute.h
@@ -158,22 +158,22 @@ CATALOG(pg_attribute,1249,AttributeRelationId) BKI_BOOTSTRAP BKI_ROWTYPE_OID(75,
 	/* Number of times inherited from direct parent relation(s) */
 	int16		attinhcount BKI_DEFAULT(0);
 
+	/* attribute's collation, if any */
+	Oid			attcollation BKI_LOOKUP_OPT(pg_collation);
+
+#ifdef CATALOG_VARLEN			/* variable-length fields start here */
+	/* NOTE: The following fields are not present in tuple descriptors. */
+
 	/*
 	 * 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
+	 * not wish to collect any stats about this column. A NULL here indicates
 	 * that no value has been explicitly set for this column, so ANALYZE
 	 * should use the default setting.
 	 *
 	 * int16 is sufficient for the current max value (MAX_STATISTICS_TARGET).
 	 */
-	int16		attstattarget BKI_DEFAULT(-1);
-
-	/* attribute's collation, if any */
-	Oid			attcollation BKI_LOOKUP_OPT(pg_collation);
-
-#ifdef CATALOG_VARLEN			/* variable-length fields start here */
-	/* NOTE: The following fields are not present in tuple descriptors. */
+	int16		attstattarget BKI_DEFAULT(_null_) BKI_FORCE_NULL;
 
 	/* Column-level access permissions */
 	aclitem		attacl[1] BKI_DEFAULT(_null_);
diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index 4af02940c5..ea096ee8a8 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -121,7 +121,7 @@ typedef struct VacAttrStats
 	 * than the underlying column/expression.  Therefore, use these fields for
 	 * information about the datatype being fed to the typanalyze function.
 	 */
-	int			attstattarget;
+	int			attstattarget;	/* -1 to use default */
 	Oid			attrtypid;		/* type of data being analyzed */
 	int32		attrtypmod;		/* typmod of data being analyzed */
 	Form_pg_type attrtype;		/* copy of pg_type row for attrtypid */
diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out
index acfd9d1f4f..b63182d5e6 100644
--- a/src/test/regress/expected/create_index.out
+++ b/src/test/regress/expected/create_index.out
@@ -2706,8 +2706,8 @@ SELECT attrelid::regclass, attnum, attstattarget
          attrelid          | attnum | attstattarget 
 ---------------------------+--------+---------------
  concur_exprs_index_expr   |      1 |           100
- concur_exprs_index_pred   |      1 |            -1
- concur_exprs_index_pred_2 |      1 |            -1
+ concur_exprs_index_pred   |      1 |              
+ concur_exprs_index_pred_2 |      1 |              
 (3 rows)
 
 DROP TABLE concur_exprs_tab;

base-commit: b8ba7344e9eb9bb505a92900b2a59257ef718135
-- 
2.43.0