1 files changed, 116 insertions, 1 deletions

diff --git a/src/backend/catalog/pg_constraint.c b/src/backend/catalog/pg_constraint.c
index 45a99af774e..aaf3537d3f5 100644
--- a/src/backend/catalog/pg_constraint.c
+++ b/src/backend/catalog/pg_constraint.c
@@ -19,6 +19,7 @@
 #include "access/htup_details.h"
 #include "access/sysattr.h"
 #include "access/table.h"
+#include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
 #include "catalog/heap.h"
@@ -933,6 +934,8 @@ RemoveConstraintById(Oid conId)
 	Relation	conDesc;
 	HeapTuple	tup;
 	Form_pg_constraint con;
+	bool		dropping_pk = false;
+	List	   *unconstrained_cols = NIL;
 
 	conDesc = table_open(ConstraintRelationId, RowExclusiveLock);
 
@@ -957,7 +960,9 @@ RemoveConstraintById(Oid conId)
 		/*
 		 * We need to update the relchecks count if it is a check constraint
 		 * being dropped.  This update will force backends to rebuild relcache
-		 * entries when we commit.
+		 * entries when we commit.  For not-null and primary key constraints,
+		 * obtain the list of columns affected, so that we can reset their
+		 * attnotnull flags below.
 		 */
 		if (con->contype == CONSTRAINT_CHECK)
 		{
@@ -984,6 +989,36 @@ RemoveConstraintById(Oid conId)
 
 			table_close(pgrel, RowExclusiveLock);
 		}
+		else if (con->contype == CONSTRAINT_NOTNULL)
+		{
+			unconstrained_cols = list_make1_int(extractNotNullColumn(tup));
+		}
+		else if (con->contype == CONSTRAINT_PRIMARY)
+		{
+			Datum		adatum;
+			ArrayType  *arr;
+			int			numkeys;
+			bool		isNull;
+			int16	   *attnums;
+
+			dropping_pk = true;
+
+			adatum = heap_getattr(tup, Anum_pg_constraint_conkey,
+								  RelationGetDescr(conDesc), &isNull);
+			if (isNull)
+				elog(ERROR, "null conkey for constraint %u", con->oid);
+			arr = DatumGetArrayTypeP(adatum);	/* ensure not toasted */
+			numkeys = ARR_DIMS(arr)[0];
+			if (ARR_NDIM(arr) != 1 ||
+				numkeys < 0 ||
+				ARR_HASNULL(arr) ||
+				ARR_ELEMTYPE(arr) != INT2OID)
+				elog(ERROR, "conkey is not a 1-D smallint array");
+			attnums = (int16 *) ARR_DATA_PTR(arr);
+
+			for (int i = 0; i < numkeys; i++)
+				unconstrained_cols = lappend_int(unconstrained_cols, attnums[i]);
+		}
 
 		/* Keep lock on constraint's rel until end of xact */
 		table_close(rel, NoLock);
@@ -1003,6 +1038,86 @@ RemoveConstraintById(Oid conId)
 	/* Fry the constraint itself */
 	CatalogTupleDelete(conDesc, &tup->t_self);
 
+	/*
+	 * If this was a NOT NULL or the primary key, the constrained columns must
+	 * have had pg_attribute.attnotnull set.  See if we need to reset it, and
+	 * do so.
+	 */
+	if (unconstrained_cols != NIL)
+	{
+		Relation	tablerel;
+		Relation	attrel;
+		Bitmapset  *pkcols;
+		ListCell   *lc;
+
+		/* Make the above deletion visible */
+		CommandCounterIncrement();
+
+		tablerel = table_open(con->conrelid, NoLock);	/* already have lock */
+		attrel = table_open(AttributeRelationId, RowExclusiveLock);
+
+		/*
+		 * We want to test columns for their presence in the primary key, but
+		 * only if we're not dropping it.
+		 */
+		pkcols = dropping_pk ? NULL :
+			RelationGetIndexAttrBitmap(tablerel,
+									   INDEX_ATTR_BITMAP_PRIMARY_KEY);
+
+		foreach(lc, unconstrained_cols)
+		{
+			AttrNumber	attnum = lfirst_int(lc);
+			HeapTuple	atttup;
+			HeapTuple	contup;
+			Bitmapset  *ircols;
+			Form_pg_attribute attForm;
+
+			/*
+			 * Obtain pg_attribute tuple and verify conditions on it.  We use
+			 * a copy we can scribble on.
+			 */
+			atttup = SearchSysCacheCopyAttNum(con->conrelid, attnum);
+			if (!HeapTupleIsValid(atttup))
+				elog(ERROR, "cache lookup failed for attribute %d of relation %u",
+					 attnum, con->conrelid);
+			attForm = (Form_pg_attribute) GETSTRUCT(atttup);
+
+			/*
+			 * Since the above deletion has been made visible, we can now
+			 * search for any remaining constraints setting this column as
+			 * not-nullable; if we find any, no need to reset attnotnull.
+			 */
+			if (bms_is_member(attnum - FirstLowInvalidHeapAttributeNumber,
+							  pkcols))
+				continue;
+			contup = findNotNullConstraintAttnum(con->conrelid, attnum);
+			if (contup)
+				continue;
+
+			/*
+			 * Also no reset if the column is in the replica identity or it's
+			 * a generated column
+			 */
+			if (attForm->attidentity != '\0')
+				continue;
+			ircols = RelationGetIndexAttrBitmap(tablerel,
+												INDEX_ATTR_BITMAP_IDENTITY_KEY);
+			if (bms_is_member(attnum - FirstLowInvalidHeapAttributeNumber,
+							  ircols))
+				continue;
+
+			/* Reset attnotnull */
+			if (attForm->attnotnull)
+			{
+				attForm->attnotnull = false;
+				CatalogTupleUpdate(attrel, &atttup->t_self, atttup);
+			}
+		}
+
+		table_close(attrel, RowExclusiveLock);
+		table_close(tablerel, NoLock);
+	}
+
 	/* Clean up */
 	ReleaseSysCache(tup);
 	table_close(conDesc, RowExclusiveLock);