Allow NOT NULL constraints to be added as NOT VALID

This allows them to be added without scanning the table, and validating
them afterwards without holding access exclusive lock on the table after
any violating rows have been deleted or fixed.

Doing ALTER TABLE ... SET NOT NULL for a column that has an invalid
not-null constraint validates that constraint.  ALTER TABLE .. VALIDATE
CONSTRAINT is also supported.  There are various checks on whether an
invalid constraint is allowed in a child table when the parent table has
a valid constraint; this should match what we do for enforced/not
enforced constraints.

pg_attribute.attnotnull is now only an indicator for whether a not-null
constraint exists for the column; whether it's valid or invalid must be
queried in pg_constraint.  Applications can continue to query
pg_attribute.attnotnull as before, but now it's possible that NULL rows
are present in the column even when that's set to true.

For backend internal purposes, we cache the nullability status in
CompactAttribute->attnullability that each tuple descriptor carries
(replacing CompactAttribute.attnotnull, which was a mirror of
Form_pg_attribute.attnotnull).  During the initial tuple descriptor
creation, based on the pg_attribute scan, we set this to UNRESTRICTED if
pg_attribute.attnotnull is false, or to UNKNOWN if it's true; then we
update the latter to VALID or INVALID depending on the pg_constraint
scan.  This flag is also copied when tupledescs are copied.

Comparing tuple descs for equality must also compare the
CompactAttribute.attnullability flag and return false in case of a
mismatch.

pg_dump deals with these constraints by storing the OIDs of invalid
not-null constraints in a separate array, and running a query to obtain
their properties.  The regular table creation SQL omits them entirely.
They are then dealt with in the same way as "separate" CHECK
constraints, and dumped after the data has been loaded.  Because no
additional pg_dump infrastructure was required, we don't bump its
version number.

I decided not to bump catversion either, because the old catalog state
works perfectly in the new world.  (Trying to run with new catalog state
and the old server version would likely run into issues, however.)

System catalogs do not support invalid not-null constraints (because
commit 14e87ffa5c54 didn't allow them to have pg_constraint rows
anyway.)

Author: Rushabh Lathia <[email protected]>
Author: Jian He <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Tested-by: Ashutosh Bapat <[email protected]>
Discussion: https://postgr.es/m/CAGPqQf0KitkNack4F5CFkFi-9Dqvp29Ro=EpcWt=4_hs-Rt+bQ@mail.gmail.com

1 files changed, 227 insertions, 44 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 4397123398e..686f1850cab 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -435,6 +435,9 @@ static void QueueFKConstraintValidation(List **wqueue, Relation conrel, Relation
 static void QueueCheckConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 										   char *constrName, HeapTuple contuple,
 										   bool recurse, bool recursing, LOCKMODE lockmode);
+static void QueueNNConstraintValidation(List **wqueue, Relation conrel, Relation rel,
+										HeapTuple contuple, bool recurse, bool recursing,
+										LOCKMODE lockmode);
 static int	transformColumnNameList(Oid relId, List *colList,
 									int16 *attnums, Oid *atttypids, Oid *attcollids);
 static int	transformFkeyGetPrimaryKey(Relation pkrel, Oid *indexOid,
@@ -498,7 +501,7 @@ static void add_column_collation_dependency(Oid relid, int32 attnum, Oid collid)
 static ObjectAddress ATExecDropNotNull(Relation rel, const char *colName, bool recurse,
 									   LOCKMODE lockmode);
 static void set_attnotnull(List **wqueue, Relation rel, AttrNumber attnum,
-						   LOCKMODE lockmode);
+						   bool is_valid, bool queue_validation);
 static ObjectAddress ATExecSetNotNull(List **wqueue, Relation rel,
 									  char *constrname, char *colName,
 									  bool recurse, bool recursing,
@@ -1340,7 +1343,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 	nncols = AddRelationNotNullConstraints(rel, stmt->nnconstraints,
 										   old_notnulls);
 	foreach_int(attrnum, nncols)
-		set_attnotnull(NULL, rel, attrnum, NoLock);
+		set_attnotnull(NULL, rel, attrnum, true, false);
 
 	ObjectAddressSet(address, RelationRelationId, relationId);
 
@@ -2738,7 +2741,7 @@ MergeAttributes(List *columns, const List *supers, char relpersistence,
 
 		/*
 		 * Request attnotnull on columns that have a not-null constraint
-		 * that's not marked NO INHERIT.
+		 * that's not marked NO INHERIT (even if not valid).
 		 */
 		nnconstrs = RelationGetNotNullConstraints(RelationGetRelid(relation),
 												  true, false);
@@ -6207,24 +6210,28 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap)
 	{
 		/*
 		 * If we are rebuilding the tuples OR if we added any new but not
-		 * verified not-null constraints, check all not-null constraints. This
-		 * is a bit of overkill but it minimizes risk of bugs.
+		 * verified not-null constraints, check all *valid* not-null
+		 * constraints. This is a bit of overkill but it minimizes risk of
+		 * bugs.
 		 *
-		 * notnull_attrs does *not* collect attribute numbers for not-null
-		 * constraints over virtual generated columns; instead, they are
-		 * collected in notnull_virtual_attrs.
+		 * notnull_attrs does *not* collect attribute numbers for valid
+		 * not-null constraints over virtual generated columns; instead, they
+		 * are collected in notnull_virtual_attrs for verification elsewhere.
 		 */
 		for (i = 0; i < newTupDesc->natts; i++)
 		{
-			Form_pg_attribute attr = TupleDescAttr(newTupDesc, i);
+			CompactAttribute *attr = TupleDescCompactAttr(newTupDesc, i);
 
-			if (attr->attnotnull && !attr->attisdropped)
+			if (attr->attnullability == ATTNULLABLE_VALID &&
+				!attr->attisdropped)
 			{
-				if (attr->attgenerated != ATTRIBUTE_GENERATED_VIRTUAL)
-					notnull_attrs = lappend_int(notnull_attrs, attr->attnum);
+				Form_pg_attribute wholeatt = TupleDescAttr(newTupDesc, i);
+
+				if (wholeatt->attgenerated != ATTRIBUTE_GENERATED_VIRTUAL)
+					notnull_attrs = lappend_int(notnull_attrs, wholeatt->attnum);
 				else
 					notnull_virtual_attrs = lappend_int(notnull_virtual_attrs,
-														attr->attnum);
+														wholeatt->attnum);
 			}
 		}
 		if (notnull_attrs || notnull_virtual_attrs)
@@ -7809,18 +7816,23 @@ ATExecDropNotNull(Relation rel, const char *colName, bool recurse,
 }
 
 /*
- * Helper to set pg_attribute.attnotnull if it isn't set, and to tell phase 3
- * to verify it.
+ * set_attnotnull
+ *		Helper to update/validate the pg_attribute status of a not-null
+ *		constraint
  *
- * When called to alter an existing table, 'wqueue' must be given so that we
- * can queue a check that existing tuples pass the constraint.  When called
- * from table creation, 'wqueue' should be passed as NULL.
+ * pg_attribute.attnotnull is set true, if it isn't already.
+ * If queue_validation is true, also set up wqueue to validate the constraint.
+ * wqueue may be given as NULL when validation is not needed (e.g., on table
+ * creation).
  */
 static void
 set_attnotnull(List **wqueue, Relation rel, AttrNumber attnum,
-			   LOCKMODE lockmode)
+			   bool is_valid, bool queue_validation)
 {
 	Form_pg_attribute attr;
+	CompactAttribute *thisatt;
+
+	Assert(!queue_validation || wqueue);
 
 	CheckAlterTableIsSafe(rel);
 
@@ -7844,8 +7856,11 @@ set_attnotnull(List **wqueue, Relation rel, AttrNumber attnum,
 			elog(ERROR, "cache lookup failed for attribute %d of relation %u",
 				 attnum, RelationGetRelid(rel));
 
+		thisatt = TupleDescCompactAttr(RelationGetDescr(rel), attnum - 1);
+		thisatt->attnullability = ATTNULLABLE_VALID;
+
 		attr = (Form_pg_attribute) GETSTRUCT(tuple);
-		Assert(!attr->attnotnull);
+
 		attr->attnotnull = true;
 		CatalogTupleUpdate(attr_rel, &tuple->t_self, tuple);
 
@@ -7853,7 +7868,8 @@ set_attnotnull(List **wqueue, Relation rel, AttrNumber attnum,
 		 * If the nullness isn't already proven by validated constraints, have
 		 * ALTER TABLE phase 3 test for it.
 		 */
-		if (wqueue && !NotNullImpliedByRelConstraints(rel, attr))
+		if (queue_validation && wqueue &&
+			!NotNullImpliedByRelConstraints(rel, attr))
 		{
 			AlteredTableInfo *tab;
 
@@ -7866,6 +7882,10 @@ set_attnotnull(List **wqueue, Relation rel, AttrNumber attnum,
 		table_close(attr_rel, RowExclusiveLock);
 		heap_freetuple(tuple);
 	}
+	else
+	{
+		CacheInvalidateRelcache(rel);
+	}
 }
 
 /*
@@ -7951,6 +7971,15 @@ ATExecSetNotNull(List **wqueue, Relation rel, char *conName, char *colName,
 			conForm->conislocal = true;
 			changed = true;
 		}
+		else if (!conForm->convalidated)
+		{
+			/*
+			 * Flip attnotnull and convalidated, and also validate the
+			 * constraint.
+			 */
+			return ATExecValidateConstraint(wqueue, rel, NameStr(conForm->conname),
+											recurse, recursing, lockmode);
+		}
 
 		if (changed)
 		{
@@ -8013,8 +8042,8 @@ ATExecSetNotNull(List **wqueue, Relation rel, char *conName, char *colName,
 	InvokeObjectPostAlterHook(RelationRelationId,
 							  RelationGetRelid(rel), attnum);
 
-	/* Mark pg_attribute.attnotnull for the column */
-	set_attnotnull(wqueue, rel, attnum, lockmode);
+	/* Mark pg_attribute.attnotnull for the column and queue validation */
+	set_attnotnull(wqueue, rel, attnum, true, true);
 
 	/*
 	 * Recurse to propagate the constraint to children that don't have one.
@@ -9417,7 +9446,6 @@ ATPrepAddPrimaryKey(List **wqueue, Relation rel, AlterTableCmd *cmd,
 					bool recurse, LOCKMODE lockmode,
 					AlterTableUtilityContext *context)
 {
-	ListCell   *lc;
 	Constraint *pkconstr;
 
 	pkconstr = castNode(Constraint, cmd->def);
@@ -9436,33 +9464,73 @@ ATPrepAddPrimaryKey(List **wqueue, Relation rel, AlterTableCmd *cmd,
 											 lockmode);
 		foreach_oid(childrelid, children)
 		{
-			foreach(lc, pkconstr->keys)
+			foreach_node(String, attname, pkconstr->keys)
 			{
 				HeapTuple	tup;
 				Form_pg_attribute attrForm;
-				char	   *attname = strVal(lfirst(lc));
 
-				tup = SearchSysCacheAttName(childrelid, attname);
+				tup = SearchSysCacheAttName(childrelid, strVal(attname));
 				if (!tup)
 					elog(ERROR, "cache lookup failed for attribute %s of relation %u",
-						 attname, childrelid);
+						 strVal(attname), childrelid);
 				attrForm = (Form_pg_attribute) GETSTRUCT(tup);
 				if (!attrForm->attnotnull)
 					ereport(ERROR,
 							errmsg("column \"%s\" of table \"%s\" is not marked NOT NULL",
-								   attname, get_rel_name(childrelid)));
+								   strVal(attname), get_rel_name(childrelid)));
 				ReleaseSysCache(tup);
 			}
 		}
 	}
 
-	/* Insert not-null constraints in the queue for the PK columns */
-	foreach(lc, pkconstr->keys)
+	/* Verify that columns are not-null, or request that they be made so */
+	foreach_node(String, column, pkconstr->keys)
 	{
 		AlterTableCmd *newcmd;
 		Constraint *nnconstr;
+		HeapTuple	tuple;
+
+		/*
+		 * First check if a suitable constraint exists.  If it does, we don't
+		 * need to request another one.  We do need to bail out if it's not
+		 * valid, though.
+		 */
+		tuple = findNotNullConstraint(RelationGetRelid(rel), strVal(column));
+		if (tuple != NULL)
+		{
+			Form_pg_constraint conForm = (Form_pg_constraint) GETSTRUCT(tuple);
+
+			/* a NO INHERIT constraint is no good */
+			if (conForm->connoinherit)
+				ereport(ERROR,
+						errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						errmsg("cannot create primary key on column \"%s\"",
+							   strVal(column)),
+				/*- translator: third %s is a constraint characteristic such as NOT VALID */
+						errdetail("The constraint \"%s\" on column \"%s\", marked %s, is incompatible with a primary key.",
+								  NameStr(conForm->conname), strVal(column), "NO INHERIT"),
+						errhint("You will need to make it inheritable using %s.",
+								"ALTER TABLE ... ALTER CONSTRAINT ... INHERIT"));
+
+			/* an unvalidated constraint is no good */
+			if (!conForm->convalidated)
+				ereport(ERROR,
+						errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+						errmsg("cannot create primary key on column \"%s\"",
+							   strVal(column)),
+				/*- translator: third %s is a constraint characteristic such as NOT VALID */
+						errdetail("The constraint \"%s\" on column \"%s\", marked %s, is incompatible with a primary key.",
+								  NameStr(conForm->conname), strVal(column), "NOT VALID"),
+						errhint("You will need to validate it using %s.",
+								"ALTER TABLE ... VALIDATE CONSTRAINT"));
+
+			/* All good with this one; don't request another */
+			heap_freetuple(tuple);
+			continue;
+		}
 
-		nnconstr = makeNotNullConstraint(lfirst(lc));
+		/* This column is not already not-null, so add it to the queue */
+		nnconstr = makeNotNullConstraint(column);
 
 		newcmd = makeNode(AlterTableCmd);
 		newcmd->subtype = AT_AddConstraint;
@@ -9836,11 +9904,15 @@ ATAddCheckNNConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 			constr->conname = ccon->name;
 
 		/*
-		 * If adding a not-null constraint, set the pg_attribute flag and tell
-		 * phase 3 to verify existing rows, if needed.
+		 * If adding a valid not-null constraint, set the pg_attribute flag
+		 * and tell phase 3 to verify existing rows, if needed.  For an
+		 * invalid constraint, just set attnotnull, without queueing
+		 * verification.
 		 */
 		if (constr->contype == CONSTR_NOTNULL)
-			set_attnotnull(wqueue, rel, ccon->attnum, lockmode);
+			set_attnotnull(wqueue, rel, ccon->attnum,
+						   !constr->skip_validation,
+						   !constr->skip_validation);
 
 		ObjectAddressSet(address, ConstraintRelationId, ccon->conoid);
 	}
@@ -12811,11 +12883,12 @@ ATExecValidateConstraint(List **wqueue, Relation rel, char *constrName,
 
 	con = (Form_pg_constraint) GETSTRUCT(tuple);
 	if (con->contype != CONSTRAINT_FOREIGN &&
-		con->contype != CONSTRAINT_CHECK)
+		con->contype != CONSTRAINT_CHECK &&
+		con->contype != CONSTRAINT_NOTNULL)
 		ereport(ERROR,
-				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-				 errmsg("constraint \"%s\" of relation \"%s\" is not a foreign key or check constraint",
-						constrName, RelationGetRelationName(rel))));
+				errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				errmsg("constraint \"%s\" of relation \"%s\" is not a foreign key, check, or not-null constraint",
+					   constrName, RelationGetRelationName(rel)));
 
 	if (!con->conenforced)
 		ereport(ERROR,
@@ -12833,6 +12906,11 @@ ATExecValidateConstraint(List **wqueue, Relation rel, char *constrName,
 			QueueCheckConstraintValidation(wqueue, conrel, rel, constrName,
 										   tuple, recurse, recursing, lockmode);
 		}
+		else if (con->contype == CONSTRAINT_NOTNULL)
+		{
+			QueueNNConstraintValidation(wqueue, conrel, rel,
+										tuple, recurse, recursing, lockmode);
+		}
 
 		ObjectAddressSet(address, ConstraintRelationId, con->oid);
 	}
@@ -13050,6 +13128,109 @@ QueueCheckConstraintValidation(List **wqueue, Relation conrel, Relation rel,
 }
 
 /*
+ * QueueNNConstraintValidation
+ *
+ * Add an entry to the wqueue to validate the given not-null constraint in
+ * Phase 3 and update the convalidated field in the pg_constraint catalog for
+ * the specified relation and all its inheriting children.
+ */
+static void
+QueueNNConstraintValidation(List **wqueue, Relation conrel, Relation rel,
+							HeapTuple contuple, bool recurse, bool recursing,
+							LOCKMODE lockmode)
+{
+	Form_pg_constraint con;
+	AlteredTableInfo *tab;
+	HeapTuple	copyTuple;
+	Form_pg_constraint copy_con;
+	List	   *children = NIL;
+	AttrNumber	attnum;
+	char	   *colname;
+
+	con = (Form_pg_constraint) GETSTRUCT(contuple);
+	Assert(con->contype == CONSTRAINT_NOTNULL);
+
+	attnum = extractNotNullColumn(contuple);
+
+	/*
+	 * If we're recursing, we've already done this for parent, so skip it.
+	 * Also, if the constraint is a NO INHERIT constraint, we shouldn't try to
+	 * look for it in the children.
+	 *
+	 * We recurse before validating on the parent, to reduce risk of
+	 * deadlocks.
+	 */
+	if (!recursing && !con->connoinherit)
+		children = find_all_inheritors(RelationGetRelid(rel), lockmode, NULL);
+
+	colname = get_attname(RelationGetRelid(rel), attnum, false);
+	foreach_oid(childoid, children)
+	{
+		Relation	childrel;
+		HeapTuple	contup;
+		Form_pg_constraint childcon;
+		char	   *conname;
+
+		if (childoid == RelationGetRelid(rel))
+			continue;
+
+		/*
+		 * If we are told not to recurse, there had better not be any child
+		 * tables, because we can't mark the constraint on the parent valid
+		 * unless it is valid for all child tables.
+		 */
+		if (!recurse)
+			ereport(ERROR,
+					errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					errmsg("constraint must be validated on child tables too"));
+
+		/*
+		 * The column on child might have a different attnum, so search by
+		 * column name.
+		 */
+		contup = findNotNullConstraint(childoid, colname);
+		if (!contup)
+			elog(ERROR, "cache lookup failed for not-null constraint on column \"%s\" of relation \"%s\"",
+				 colname, get_rel_name(childoid));
+		childcon = (Form_pg_constraint) GETSTRUCT(contup);
+		if (childcon->convalidated)
+			continue;
+
+		/* find_all_inheritors already got lock */
+		childrel = table_open(childoid, NoLock);
+		conname = pstrdup(NameStr(childcon->conname));
+
+		/* XXX improve ATExecValidateConstraint API to avoid double search */
+		ATExecValidateConstraint(wqueue, childrel, conname,
+								 false, true, lockmode);
+		table_close(childrel, NoLock);
+	}
+
+	/* Set attnotnull appropriately without queueing another validation */
+	set_attnotnull(NULL, rel, attnum, true, false);
+
+	tab = ATGetQueueEntry(wqueue, rel);
+	tab->verify_new_notnull = true;
+
+	/*
+	 * Invalidate relcache so that others see the new validated constraint.
+	 */
+	CacheInvalidateRelcache(rel);
+
+	/*
+	 * Now update the catalogs, while we have the door open.
+	 */
+	copyTuple = heap_copytuple(contuple);
+	copy_con = (Form_pg_constraint) GETSTRUCT(copyTuple);
+	copy_con->convalidated = true;
+	CatalogTupleUpdate(conrel, &copyTuple->t_self, copyTuple);
+
+	InvokeObjectPostAlterHook(ConstraintRelationId, con->oid, 0);
+
+	heap_freetuple(copyTuple);
+}
+
+/*
  * transformColumnNameList - transform list of column names
  *
  * Lookup each name and return its attnum and, optionally, type and collation
@@ -19770,17 +19951,19 @@ PartConstraintImpliedByRelConstraint(Relation scanrel,
 
 		for (i = 1; i <= natts; i++)
 		{
-			Form_pg_attribute att = TupleDescAttr(scanrel->rd_att, i - 1);
+			CompactAttribute *att = TupleDescCompactAttr(scanrel->rd_att, i - 1);
 
-			if (att->attnotnull && !att->attisdropped)
+			/* invalid not-null constraint must be ignored here */
+			if (att->attnullability == ATTNULLABLE_VALID && !att->attisdropped)
 			{
+				Form_pg_attribute wholeatt = TupleDescAttr(scanrel->rd_att, i - 1);
 				NullTest   *ntest = makeNode(NullTest);
 
 				ntest->arg = (Expr *) makeVar(1,
 											  i,
-											  att->atttypid,
-											  att->atttypmod,
-											  att->attcollation,
+											  wholeatt->atttypid,
+											  wholeatt->atttypmod,
+											  wholeatt->attcollation,
 											  0);
 				ntest->nulltesttype = IS_NOT_NULL;