Include result relation info in direct modify ForeignScan nodes.

FDWs that can perform an UPDATE/DELETE remotely using the "direct modify"
set of APIs need to access the ResultRelInfo of the target table. That's
currently available in EState.es_result_relation_info, but the next
commit will remove that field.

This commit adds a new resultRelation field in ForeignScan, to store the
target relation's RT index, and the corresponding ResultRelInfo in
ForeignScanState. The FDW's PlanDirectModify callback is expected to set
'resultRelation' along with 'operation'. The core code doesn't need them
for anything, they are for the convenience of FDW's Begin- and
IterateDirectModify callbacks.

Authors: Amit Langote, Etsuro Fujita
Discussion: https://www.postgresql.org/message-id/CA%2BHiwqGEmiib8FLiHMhKB%2BCH5dRgHSLc5N5wnvc4kym%2BZYpQEQ%40mail.gmail.com

8 files changed, 27 insertions, 0 deletions

diff --git a/src/backend/executor/nodeForeignscan.c b/src/backend/executor/nodeForeignscan.c
index 513471ab9b9..0b20f94035e 100644
--- a/src/backend/executor/nodeForeignscan.c
+++ b/src/backend/executor/nodeForeignscan.c
@@ -215,6 +215,13 @@ ExecInitForeignScan(ForeignScan *node, EState *estate, int eflags)
 	scanstate->fdwroutine = fdwroutine;
 	scanstate->fdw_state = NULL;
 
+	/*
+	 * For the FDW's convenience, look up the modification target relation's.
+	 * ResultRelInfo.
+	 */
+	if (node->resultRelation > 0)
+		scanstate->resultRelInfo = estate->es_result_relations[node->resultRelation - 1];
+
 	/* Initialize any outer plan. */
 	if (outerPlan(node))
 		outerPlanState(scanstate) =
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 4d79f70950b..2b4d7654cc7 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -758,6 +758,7 @@ _copyForeignScan(const ForeignScan *from)
 	COPY_NODE_FIELD(fdw_recheck_quals);
 	COPY_BITMAPSET_FIELD(fs_relids);
 	COPY_SCALAR_FIELD(fsSystemCol);
+	COPY_SCALAR_FIELD(resultRelation);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/outfuncs.c b/src/backend/nodes/outfuncs.c
index f441ae3c519..08a049232e0 100644
--- a/src/backend/nodes/outfuncs.c
+++ b/src/backend/nodes/outfuncs.c
@@ -695,6 +695,7 @@ _outForeignScan(StringInfo str, const ForeignScan *node)
 	WRITE_NODE_FIELD(fdw_recheck_quals);
 	WRITE_BITMAPSET_FIELD(fs_relids);
 	WRITE_BOOL_FIELD(fsSystemCol);
+	WRITE_INT_FIELD(resultRelation);
 }
 
 static void
diff --git a/src/backend/nodes/readfuncs.c b/src/backend/nodes/readfuncs.c
index 3a54765f5ca..ab7b535caae 100644
--- a/src/backend/nodes/readfuncs.c
+++ b/src/backend/nodes/readfuncs.c
@@ -2014,6 +2014,7 @@ _readForeignScan(void)
 	READ_NODE_FIELD(fdw_recheck_quals);
 	READ_BITMAPSET_FIELD(fs_relids);
 	READ_BOOL_FIELD(fsSystemCol);
+	READ_INT_FIELD(resultRelation);
 
 	READ_DONE();
 }
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 881eaf48133..94280a730c4 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -5530,7 +5530,11 @@ make_foreignscan(List *qptlist,
 	plan->lefttree = outer_plan;
 	plan->righttree = NULL;
 	node->scan.scanrelid = scanrelid;
+
+	/* these may be overridden by the FDW's PlanDirectModify callback. */
 	node->operation = CMD_SELECT;
+	node->resultRelation = 0;
+
 	/* fs_server will be filled in by create_foreignscan_plan */
 	node->fs_server = InvalidOid;
 	node->fdw_exprs = fdw_exprs;
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 6847ff6f447..8b433714259 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1310,6 +1310,10 @@ set_foreignscan_references(PlannerInfo *root,
 	}
 
 	fscan->fs_relids = offset_relid_set(fscan->fs_relids, rtoffset);
+
+	/* Adjust resultRelation if it's valid */
+	if (fscan->resultRelation > 0)
+		fscan->resultRelation += rtoffset;
 }
 
 /*
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index a926ff17118..d9b09c59206 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1777,6 +1777,7 @@ typedef struct ForeignScanState
 	ScanState	ss;				/* its first field is NodeTag */
 	ExprState  *fdw_recheck_quals;	/* original quals not in ss.ps.qual */
 	Size		pscan_len;		/* size of parallel coordination information */
+	ResultRelInfo *resultRelInfo;	/* result rel info, if UPDATE or DELETE */
 	/* use struct pointer to avoid including fdwapi.h here */
 	struct FdwRoutine *fdwroutine;
 	void	   *fdw_state;		/* foreign-data wrapper can keep state here */
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index a7bdf3497e1..7e6b10f86b9 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -599,12 +599,20 @@ typedef struct WorkTableScan
  * When the plan node represents a foreign join, scan.scanrelid is zero and
  * fs_relids must be consulted to identify the join relation.  (fs_relids
  * is valid for simple scans as well, but will always match scan.scanrelid.)
+ *
+ * If the FDW's PlanDirectModify() callback decides to repurpose a ForeignScan
+ * node to perform the UPDATE or DELETE operation directly in the remote
+ * server, it sets 'operation' and 'resultRelation' to identify the operation
+ * type and target relation.  Note that these fields are only set if the
+ * modification is performed *fully* remotely; otherwise, the modification is
+ * driven by a local ModifyTable node and 'operation' is left to CMD_SELECT.
  * ----------------
  */
 typedef struct ForeignScan
 {
 	Scan		scan;
 	CmdType		operation;		/* SELECT/INSERT/UPDATE/DELETE */
+	Index		resultRelation; /* direct modification target's RT index */
 	Oid			fs_server;		/* OID of foreign server */
 	List	   *fdw_exprs;		/* expressions that FDW may evaluate */
 	List	   *fdw_private;	/* private data for FDW */