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, 37 insertions, 5 deletions

diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
index 288b29e44a9..1f2a23bcdd6 100644
--- a/src/backend/executor/execMain.c
+++ b/src/backend/executor/execMain.c
@@ -44,6 +44,7 @@
 #include "catalog/namespace.h"
 #include "commands/trigger.h"
 #include "executor/execdebug.h"
+#include "foreign/fdwapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
 #include "optimizer/clauses.h"
@@ -1005,6 +1006,7 @@ void
 CheckValidResultRel(Relation resultRel, CmdType operation)
 {
 	TriggerDesc *trigDesc = resultRel->trigdesc;
+	FdwRoutine *fdwroutine;
 
 	switch (resultRel->rd_rel->relkind)
 	{
@@ -1069,10 +1071,35 @@ CheckValidResultRel(Relation resultRel, CmdType operation)
 							RelationGetRelationName(resultRel))));
 			break;
 		case RELKIND_FOREIGN_TABLE:
-			ereport(ERROR,
-					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-					 errmsg("cannot change foreign table \"%s\"",
-							RelationGetRelationName(resultRel))));
+			/* Okay only if the FDW supports it */
+			fdwroutine = GetFdwRoutineForRelation(resultRel, false);
+			switch (operation)
+			{
+				case CMD_INSERT:
+					if (fdwroutine->ExecForeignInsert == NULL)
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("cannot insert into foreign table \"%s\"",
+										RelationGetRelationName(resultRel))));
+					break;
+				case CMD_UPDATE:
+					if (fdwroutine->ExecForeignUpdate == NULL)
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("cannot update foreign table \"%s\"",
+										RelationGetRelationName(resultRel))));
+					break;
+				case CMD_DELETE:
+					if (fdwroutine->ExecForeignDelete == NULL)
+						ereport(ERROR,
+								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+								 errmsg("cannot delete from foreign table \"%s\"",
+										RelationGetRelationName(resultRel))));
+					break;
+				default:
+					elog(ERROR, "unrecognized CmdType: %d", (int) operation);
+					break;
+			}
 			break;
 		default:
 			ereport(ERROR,
@@ -1126,7 +1153,7 @@ CheckValidRowMarkRel(Relation rel, RowMarkType markType)
 							RelationGetRelationName(rel))));
 			break;
 		case RELKIND_FOREIGN_TABLE:
-			/* Perhaps we can support this someday, but not today */
+			/* Should not get here */
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 					 errmsg("cannot lock rows in foreign table \"%s\"",
@@ -1180,6 +1207,11 @@ InitResultRelInfo(ResultRelInfo *resultRelInfo,
 		resultRelInfo->ri_TrigWhenExprs = NULL;
 		resultRelInfo->ri_TrigInstrument = NULL;
 	}
+	if (resultRelationDesc->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
+		resultRelInfo->ri_FdwRoutine = GetFdwRoutineForRelation(resultRelationDesc, true);
+	else
+		resultRelInfo->ri_FdwRoutine = NULL;
+	resultRelInfo->ri_FdwState = NULL;
 	resultRelInfo->ri_ConstraintExprs = NULL;
 	resultRelInfo->ri_junkFilter = NULL;
 	resultRelInfo->ri_projectReturning = NULL;