Save a few bytes in pg_attribute

Change the columns attndims, attstattarget, and attinhcount from int32
to int16, and reorder a bit.  This saves some space (currently 4
bytes) in pg_attribute and tuple descriptors, which translates into
small performance benefits and/or room for new columns in pg_attribute
needed by future features.

attndims and attinhcount are never realistically used with values
larger than int16.  Just to be sure, add some overflow checks.
attstattarget is currently limited explicitly to 10000.

For consistency, pg_constraint.coninhcount is also changed like
attinhcount.

Discussion: https://www.postgresql.org/message-id/flat/d07ffc2b-e0e8-77f7-38fb-be921dff71af%40enterprisedb.com

1 files changed, 28 insertions, 0 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index c510a01fd8d..3147dddf286 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -2650,6 +2650,10 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 				 */
 
 				def->inhcount++;
+				if (def->inhcount < 0)
+					ereport(ERROR,
+							errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+							errmsg("too many inheritance parents"));
 
 				newattmap->attnums[parent_attno - 1] = exist_attno;
 			}
@@ -3173,6 +3177,10 @@ MergeCheckConstraint(List *constraints, char *name, Node *expr)
 		{
 			/* OK to merge */
 			ccon->inhcount++;
+			if (ccon->inhcount < 0)
+				ereport(ERROR,
+						errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+						errmsg("too many inheritance parents"));
 			return true;
 		}
 
@@ -6828,6 +6836,10 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 
 			/* Bump the existing child att's inhcount */
 			childatt->attinhcount++;
+			if (childatt->attinhcount < 0)
+				ereport(ERROR,
+						errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+						errmsg("too many inheritance parents"));
 			CatalogTupleUpdate(attrdesc, &tuple->t_self, tuple);
 
 			heap_freetuple(tuple);
@@ -6919,6 +6931,10 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	attribute.attstattarget = (newattnum > 0) ? -1 : 0;
 	attribute.attlen = tform->typlen;
 	attribute.attnum = newattnum;
+	if (list_length(colDef->typeName->arrayBounds) > PG_INT16_MAX)
+		ereport(ERROR,
+				errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				errmsg("too many array dimensions"));
 	attribute.attndims = list_length(colDef->typeName->arrayBounds);
 	attribute.atttypmod = typmod;
 	attribute.attbyval = tform->typbyval;
@@ -12924,6 +12940,10 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 	attTup->atttypid = targettype;
 	attTup->atttypmod = targettypmod;
 	attTup->attcollation = targetcollid;
+	if (list_length(typeName->arrayBounds) > PG_INT16_MAX)
+		ereport(ERROR,
+				errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				errmsg("too many array dimensions"));
 	attTup->attndims = list_length(typeName->arrayBounds);
 	attTup->attlen = tform->typlen;
 	attTup->attbyval = tform->typbyval;
@@ -15155,6 +15175,10 @@ MergeAttributesIntoExisting(Relation child_rel, Relation parent_rel)
 			 * later on, this change will just roll back.)
 			 */
 			childatt->attinhcount++;
+			if (childatt->attinhcount < 0)
+				ereport(ERROR,
+						errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+						errmsg("too many inheritance parents"));
 
 			/*
 			 * In case of partitions, we must enforce that value of attislocal
@@ -15292,6 +15316,10 @@ MergeConstraintsIntoExisting(Relation child_rel, Relation parent_rel)
 			child_copy = heap_copytuple(child_tuple);
 			child_con = (Form_pg_constraint) GETSTRUCT(child_copy);
 			child_con->coninhcount++;
+			if (child_con->coninhcount < 0)
+				ereport(ERROR,
+						errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+						errmsg("too many inheritance parents"));
 
 			/*
 			 * In case of partitions, an inherited constraint must be