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

3 files changed, 191 insertions, 44 deletions

diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 75b45f7cd5d..366c4af27fa 100644
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -297,9 +297,8 @@ analyze_rel(Oid relid, RangeVar *relation, int options, List *va_cols,
  *	do_analyze_rel() -- analyze one relation, recursively or not
  *
  * Note that "acquirefunc" is only relevant for the non-inherited case.
- * If we supported foreign tables in inheritance trees,
- * acquire_inherited_sample_rows would need to determine the appropriate
- * acquirefunc for each child table.
+ * For the inherited case, acquire_inherited_sample_rows() determines the
+ * appropriate acquirefunc for each child table.
  */
 static void
 do_analyze_rel(Relation onerel, int options, List *va_cols,
@@ -1448,7 +1447,8 @@ compare_rows(const void *a, const void *b)
  *
  * This has the same API as acquire_sample_rows, except that rows are
  * collected from all inheritance children as well as the specified table.
- * We fail and return zero if there are no inheritance children.
+ * We fail and return zero if there are no inheritance children, or if all
+ * children are foreign tables that don't support ANALYZE.
  */
 static int
 acquire_inherited_sample_rows(Relation onerel, int elevel,
@@ -1457,6 +1457,7 @@ acquire_inherited_sample_rows(Relation onerel, int elevel,
 {
 	List	   *tableOIDs;
 	Relation   *rels;
+	AcquireSampleRowsFunc *acquirefuncs;
 	double	   *relblocks;
 	double		totalblocks;
 	int			numrows,
@@ -1491,10 +1492,12 @@ acquire_inherited_sample_rows(Relation onerel, int elevel,
 	}
 
 	/*
-	 * Count the blocks in all the relations.  The result could overflow
-	 * BlockNumber, so we use double arithmetic.
+	 * Identify acquirefuncs to use, and count blocks in all the relations.
+	 * The result could overflow BlockNumber, so we use double arithmetic.
 	 */
 	rels = (Relation *) palloc(list_length(tableOIDs) * sizeof(Relation));
+	acquirefuncs = (AcquireSampleRowsFunc *)
+		palloc(list_length(tableOIDs) * sizeof(AcquireSampleRowsFunc));
 	relblocks = (double *) palloc(list_length(tableOIDs) * sizeof(double));
 	totalblocks = 0;
 	nrels = 0;
@@ -1502,6 +1505,8 @@ acquire_inherited_sample_rows(Relation onerel, int elevel,
 	{
 		Oid			childOID = lfirst_oid(lc);
 		Relation	childrel;
+		AcquireSampleRowsFunc acquirefunc = NULL;
+		BlockNumber relpages = 0;
 
 		/* We already got the needed lock */
 		childrel = heap_open(childOID, NoLock);
@@ -1515,13 +1520,67 @@ acquire_inherited_sample_rows(Relation onerel, int elevel,
 			continue;
 		}
 
+		/* Check table type (MATVIEW can't happen, but might as well allow) */
+		if (childrel->rd_rel->relkind == RELKIND_RELATION ||
+			childrel->rd_rel->relkind == RELKIND_MATVIEW)
+		{
+			/* Regular table, so use the regular row acquisition function */
+			acquirefunc = acquire_sample_rows;
+			relpages = RelationGetNumberOfBlocks(childrel);
+		}
+		else if (childrel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		{
+			/*
+			 * For a foreign table, call the FDW's hook function to see
+			 * whether it supports analysis.
+			 */
+			FdwRoutine *fdwroutine;
+			bool		ok = false;
+
+			fdwroutine = GetFdwRoutineForRelation(childrel, false);
+
+			if (fdwroutine->AnalyzeForeignTable != NULL)
+				ok = fdwroutine->AnalyzeForeignTable(childrel,
+													 &acquirefunc,
+													 &relpages);
+
+			if (!ok)
+			{
+				/* ignore, but release the lock on it */
+				Assert(childrel != onerel);
+				heap_close(childrel, AccessShareLock);
+				continue;
+			}
+		}
+		else
+		{
+			/* ignore, but release the lock on it */
+			Assert(childrel != onerel);
+			heap_close(childrel, AccessShareLock);
+			continue;
+		}
+
+		/* OK, we'll process this child */
 		rels[nrels] = childrel;
-		relblocks[nrels] = (double) RelationGetNumberOfBlocks(childrel);
-		totalblocks += relblocks[nrels];
+		acquirefuncs[nrels] = acquirefunc;
+		relblocks[nrels] = (double) relpages;
+		totalblocks += (double) relpages;
 		nrels++;
 	}
 
 	/*
+	 * If we don't have at least two tables to consider, fail.
+	 */
+	if (nrels < 2)
+	{
+		ereport(elevel,
+				(errmsg("skipping analyze of \"%s.%s\" inheritance tree --- this inheritance tree contains no analyzable child tables",
+						get_namespace_name(RelationGetNamespace(onerel)),
+						RelationGetRelationName(onerel))));
+		return 0;
+	}
+
+	/*
 	 * Now sample rows from each relation, proportionally to its fraction of
 	 * the total block count.  (This might be less than desirable if the child
 	 * rels have radically different free-space percentages, but it's not
@@ -1533,6 +1592,7 @@ acquire_inherited_sample_rows(Relation onerel, int elevel,
 	for (i = 0; i < nrels; i++)
 	{
 		Relation	childrel = rels[i];
+		AcquireSampleRowsFunc acquirefunc = acquirefuncs[i];
 		double		childblocks = relblocks[i];
 
 		if (childblocks > 0)
@@ -1549,12 +1609,9 @@ acquire_inherited_sample_rows(Relation onerel, int elevel,
 							tdrows;
 
 				/* Fetch a random sample of the child's rows */
-				childrows = acquire_sample_rows(childrel,
-												elevel,
-												rows + numrows,
-												childtargrows,
-												&trows,
-												&tdrows);
+				childrows = (*acquirefunc) (childrel, elevel,
+											rows + numrows, childtargrows,
+											&trows, &tdrows);
 
 				/* We may need to convert from child's rowtype to parent's */
 				if (childrows > 0 &&
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index a951c55ed34..315a52849c9 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -2187,6 +2187,10 @@ ExplainScanTarget(Scan *plan, ExplainState *es)
 
 /*
  * Show the target of a ModifyTable node
+ *
+ * Here we show the nominal target (ie, the relation that was named in the
+ * original query).  If the actual target(s) is/are different, we'll show them
+ * in show_modifytable_info().
  */
 static void
 ExplainModifyTarget(ModifyTable *plan, ExplainState *es)
@@ -2303,30 +2307,106 @@ ExplainTargetRel(Plan *plan, Index rti, ExplainState *es)
 
 /*
  * Show extra information for a ModifyTable node
+ *
+ * We have two objectives here.  First, if there's more than one target table
+ * or it's different from the nominal target, identify the actual target(s).
+ * Second, give FDWs a chance to display extra info about foreign targets.
  */
 static void
 show_modifytable_info(ModifyTableState *mtstate, ExplainState *es)
 {
-	FdwRoutine *fdwroutine = mtstate->resultRelInfo->ri_FdwRoutine;
+	ModifyTable *node = (ModifyTable *) mtstate->ps.plan;
+	const char *operation;
+	const char *foperation;
+	bool		labeltargets;
+	int			j;
 
-	/*
-	 * If the first target relation is a foreign table, call its FDW to
-	 * display whatever additional fields it wants to.  For now, we ignore the
-	 * possibility of other targets being foreign tables, although the API for
-	 * ExplainForeignModify is designed to allow them to be processed.
-	 */
-	if (fdwroutine != NULL &&
-		fdwroutine->ExplainForeignModify != NULL)
+	switch (node->operation)
 	{
-		ModifyTable *node = (ModifyTable *) mtstate->ps.plan;
-		List	   *fdw_private = (List *) linitial(node->fdwPrivLists);
-
-		fdwroutine->ExplainForeignModify(mtstate,
-										 mtstate->resultRelInfo,
-										 fdw_private,
-										 0,
-										 es);
+		case CMD_INSERT:
+			operation = "Insert";
+			foperation = "Foreign Insert";
+			break;
+		case CMD_UPDATE:
+			operation = "Update";
+			foperation = "Foreign Update";
+			break;
+		case CMD_DELETE:
+			operation = "Delete";
+			foperation = "Foreign Delete";
+			break;
+		default:
+			operation = "???";
+			foperation = "Foreign ???";
+			break;
+	}
+
+	/* Should we explicitly label target relations? */
+	labeltargets = (mtstate->mt_nplans > 1 ||
+					(mtstate->mt_nplans == 1 &&
+	   mtstate->resultRelInfo->ri_RangeTableIndex != node->nominalRelation));
+
+	if (labeltargets)
+		ExplainOpenGroup("Target Tables", "Target Tables", false, es);
+
+	for (j = 0; j < mtstate->mt_nplans; j++)
+	{
+		ResultRelInfo *resultRelInfo = mtstate->resultRelInfo + j;
+		FdwRoutine *fdwroutine = resultRelInfo->ri_FdwRoutine;
+
+		if (labeltargets)
+		{
+			/* Open a group for this target */
+			ExplainOpenGroup("Target Table", NULL, true, es);
+
+			/*
+			 * In text mode, decorate each target with operation type, so that
+			 * ExplainTargetRel's output of " on foo" will read nicely.
+			 */
+			if (es->format == EXPLAIN_FORMAT_TEXT)
+			{
+				appendStringInfoSpaces(es->str, es->indent * 2);
+				appendStringInfoString(es->str,
+									   fdwroutine ? foperation : operation);
+			}
+
+			/* Identify target */
+			ExplainTargetRel((Plan *) node,
+							 resultRelInfo->ri_RangeTableIndex,
+							 es);
+
+			if (es->format == EXPLAIN_FORMAT_TEXT)
+			{
+				appendStringInfoChar(es->str, '\n');
+				es->indent++;
+			}
+		}
+
+		/* Give FDW a chance */
+		if (fdwroutine && fdwroutine->ExplainForeignModify != NULL)
+		{
+			List	   *fdw_private = (List *) list_nth(node->fdwPrivLists, j);
+
+			fdwroutine->ExplainForeignModify(mtstate,
+											 resultRelInfo,
+											 fdw_private,
+											 j,
+											 es);
+		}
+
+		if (labeltargets)
+		{
+			/* Undo the indentation we added in text format */
+			if (es->format == EXPLAIN_FORMAT_TEXT)
+				es->indent--;
+
+			/* Close the group */
+			ExplainCloseGroup("Target Table", NULL, true, es);
+		}
 	}
+
+	if (labeltargets)
+		ExplainCloseGroup("Target Tables", "Target Tables", false, es);
 }
 
 /*
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 &&