Support writable foreign tables.

This patch adds the core-system infrastructure needed to support updates
on foreign tables, and extends contrib/postgres_fdw to allow updates
against remote Postgres servers.  There's still a great deal of room for
improvement in optimization of remote updates, but at least there's basic
functionality there now.

KaiGai Kohei, reviewed by Alexander Korotkov and Laurenz Albe, and rather
heavily revised by Tom Lane.

1 files changed, 34 insertions, 1 deletions

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 989b52da9d4..9799e9ecb41 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -90,6 +90,7 @@ static void ExplainIndexScanDetails(Oid indexid, ScanDirection indexorderdir,
 static void ExplainScanTarget(Scan *plan, ExplainState *es);
 static void ExplainModifyTarget(ModifyTable *plan, ExplainState *es);
 static void ExplainTargetRel(Plan *plan, Index rti, ExplainState *es);
+static void show_modifytable_info(ModifyTableState *mtstate, ExplainState *es);
 static void ExplainMemberNodes(List *plans, PlanState **planstates,
 				   List *ancestors, ExplainState *es);
 static void ExplainSubPlans(List *plans, List *ancestors,
@@ -1341,6 +1342,9 @@ ExplainNode(PlanState *planstate, List *ancestors,
 				show_instrumentation_count("Rows Removed by Filter", 1,
 										   planstate, es);
 			break;
+		case T_ModifyTable:
+			show_modifytable_info((ModifyTableState *) planstate, es);
+			break;
 		case T_Hash:
 			show_hash_info((HashState *) planstate, es);
 			break;
@@ -1840,7 +1844,8 @@ show_foreignscan_info(ForeignScanState *fsstate, ExplainState *es)
 	FdwRoutine *fdwroutine = fsstate->fdwroutine;
 
 	/* Let the FDW emit whatever fields it wants */
-	fdwroutine->ExplainForeignScan(fsstate, es);
+	if (fdwroutine->ExplainForeignScan != NULL)
+		fdwroutine->ExplainForeignScan(fsstate, es);
 }
 
 /*
@@ -2037,6 +2042,34 @@ ExplainTargetRel(Plan *plan, Index rti, ExplainState *es)
 }
 
 /*
+ * Show extra information for a ModifyTable node
+ */
+static void
+show_modifytable_info(ModifyTableState *mtstate, ExplainState *es)
+{
+	FdwRoutine *fdwroutine = mtstate->resultRelInfo->ri_FdwRoutine;
+
+	/*
+	 * 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)
+	{
+		ModifyTable *node = (ModifyTable *) mtstate->ps.plan;
+		List	   *fdw_private = (List *) linitial(node->fdwPrivLists);
+
+		fdwroutine->ExplainForeignModify(mtstate,
+										 mtstate->resultRelInfo,
+										 fdw_private,
+										 0,
+										 es);
+	}
+}
+
+/*
  * Explain the constituent plans of a ModifyTable, Append, MergeAppend,
  * BitmapAnd, or BitmapOr node.
  *