Allow foreign tables to participate in inheritance.

Foreign tables can now be inheritance children, or parents.  Much of the
system was already ready for this, but we had to fix a few things of
course, mostly in the area of planner and executor handling of row locks.

As side effects of this, allow foreign tables to have NOT VALID CHECK
constraints (and hence to accept ALTER ... VALIDATE CONSTRAINT), and to
accept ALTER SET STORAGE and ALTER SET WITH/WITHOUT OIDS.  Continuing to
disallow these things would've required bizarre and inconsistent special
cases in inheritance behavior.  Since foreign tables don't enforce CHECK
constraints anyway, a NOT VALID one is a complete no-op, but that doesn't
mean we shouldn't allow it.  And it's possible that some FDWs might have
use for SET STORAGE or SET WITH OIDS, though doubtless they will be no-ops
for most.

An additional change in support of this is that when a ModifyTable node
has multiple target tables, they will all now be explicitly identified
in EXPLAIN output, for example:

 Update on pt1  (cost=0.00..321.05 rows=3541 width=46)
   Update on pt1
   Foreign Update on ft1
   Foreign Update on ft2
   Update on child3
   ->  Seq Scan on pt1  (cost=0.00..0.00 rows=1 width=46)
   ->  Foreign Scan on ft1  (cost=100.00..148.03 rows=1170 width=46)
   ->  Foreign Scan on ft2  (cost=100.00..148.03 rows=1170 width=46)
   ->  Seq Scan on child3  (cost=0.00..25.00 rows=1200 width=46)

This was done mainly to provide an unambiguous place to attach "Remote SQL"
fields, but it is useful for inherited updates even when no foreign tables
are involved.

Shigeru Hanada and Etsuro Fujita, reviewed by Ashutosh Bapat and Kyotaro
Horiguchi, some additional hacking by me

1 files changed, 23 insertions, 13 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 41474575055..a9f79431e5c 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -1504,10 +1504,11 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
 		 */
 		relation = heap_openrv(parent, ShareUpdateExclusiveLock);
 
-		if (relation->rd_rel->relkind != RELKIND_RELATION)
+		if (relation->rd_rel->relkind != RELKIND_RELATION &&
+			relation->rd_rel->relkind != RELKIND_FOREIGN_TABLE)
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("inherited relation \"%s\" is not a table",
+					 errmsg("inherited relation \"%s\" is not a table or foreign table",
 							parent->relname)));
 		/* Permanent rels cannot inherit from temporary ones */
 		if (relpersistence != RELPERSISTENCE_TEMP &&
@@ -3157,7 +3158,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			pass = AT_PASS_MISC;
 			break;
 		case AT_SetStorage:		/* ALTER COLUMN SET STORAGE */
-			ATSimplePermissions(rel, ATT_TABLE | ATT_MATVIEW);
+			ATSimplePermissions(rel, ATT_TABLE | ATT_MATVIEW | ATT_FOREIGN_TABLE);
 			ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
 			/* No command-specific prep needed */
 			pass = AT_PASS_MISC;
@@ -3245,14 +3246,14 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			pass = AT_PASS_MISC;
 			break;
 		case AT_AddOids:		/* SET WITH OIDS */
-			ATSimplePermissions(rel, ATT_TABLE);
+			ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 			if (!rel->rd_rel->relhasoids || recursing)
 				ATPrepAddOids(wqueue, rel, recurse, cmd, lockmode);
 			/* Recursion occurs during execution phase */
 			pass = AT_PASS_ADD_COL;
 			break;
 		case AT_DropOids:		/* SET WITHOUT OIDS */
-			ATSimplePermissions(rel, ATT_TABLE);
+			ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 			/* Performs own recursion */
 			if (rel->rd_rel->relhasoids)
 			{
@@ -3280,17 +3281,23 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			pass = AT_PASS_MISC;
 			break;
 		case AT_AddInherit:		/* INHERIT */
-			ATSimplePermissions(rel, ATT_TABLE);
+			ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 			/* This command never recurses */
 			ATPrepAddInherit(rel);
 			pass = AT_PASS_MISC;
 			break;
+		case AT_DropInherit:	/* NO INHERIT */
+			ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
+			/* This command never recurses */
+			/* No command-specific prep needed */
+			pass = AT_PASS_MISC;
+			break;
 		case AT_AlterConstraint:		/* ALTER CONSTRAINT */
 			ATSimplePermissions(rel, ATT_TABLE);
 			pass = AT_PASS_MISC;
 			break;
 		case AT_ValidateConstraint:		/* VALIDATE CONSTRAINT */
-			ATSimplePermissions(rel, ATT_TABLE);
+			ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 			/* Recursion occurs during execution phase */
 			/* No command-specific prep needed except saving recurse flag */
 			if (recurse)
@@ -3318,7 +3325,6 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 		case AT_EnableAlwaysRule:
 		case AT_EnableReplicaRule:
 		case AT_DisableRule:
-		case AT_DropInherit:	/* NO INHERIT */
 		case AT_AddOf:			/* OF */
 		case AT_DropOf: /* NOT OF */
 		case AT_EnableRowSecurity:
@@ -4637,7 +4643,7 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
 
 	/* At top level, permission check was done in ATPrepCmd, else do it */
 	if (recursing)
-		ATSimplePermissions(rel, ATT_TABLE);
+		ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 
 	attrdesc = heap_open(AttributeRelationId, RowExclusiveLock);
 
@@ -5533,7 +5539,7 @@ ATExecDropColumn(List **wqueue, Relation rel, const char *colName,
 
 	/* At top level, permission check was done in ATPrepCmd, else do it */
 	if (recursing)
-		ATSimplePermissions(rel, ATT_TABLE);
+		ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 
 	/*
 	 * get the number of the attribute
@@ -5926,7 +5932,7 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 
 	/* At top level, permission check was done in ATPrepCmd, else do it */
 	if (recursing)
-		ATSimplePermissions(rel, ATT_TABLE);
+		ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 
 	/*
 	 * Call AddRelationNewConstraints to do the work, making sure it works on
@@ -7084,6 +7090,10 @@ validateCheckConstraint(Relation rel, HeapTuple constrtup)
 	bool		isnull;
 	Snapshot	snapshot;
 
+	/* VALIDATE CONSTRAINT is a no-op for foreign tables */
+	if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		return;
+
 	constrForm = (Form_pg_constraint) GETSTRUCT(constrtup);
 
 	estate = CreateExecutorState();
@@ -7426,7 +7436,7 @@ ATExecDropConstraint(Relation rel, const char *constrName,
 
 	/* At top level, permission check was done in ATPrepCmd, else do it */
 	if (recursing)
-		ATSimplePermissions(rel, ATT_TABLE);
+		ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 
 	conrel = heap_open(ConstraintRelationId, RowExclusiveLock);
 
@@ -9681,7 +9691,7 @@ ATExecAddInherit(Relation child_rel, RangeVar *parent, LOCKMODE lockmode)
 	 * Must be owner of both parent and child -- child was checked by
 	 * ATSimplePermissions call in ATPrepCmd
 	 */
-	ATSimplePermissions(parent_rel, ATT_TABLE);
+	ATSimplePermissions(parent_rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 
 	/* Permanent rels cannot inherit from temporary ones */
 	if (parent_rel->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&