tableam: Use in CREATE TABLE AS and CREATE MATERIALIZED VIEW.

Previously those directly performed a heap_insert(). Use
table_insert() instead.  The input slot of those routines is not of
the target relation - we could fix that by copying if necessary, but
that'd not be beneficial for performance. As those codepaths don't
access any AM specific tuple fields (say xmin/xmax), there's no need
to use an AM specific slot.

Author: Andres Freund
Reviewed-By: Haribabu Kommi
Discussion: https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de

src/backend/commands/createas.c

@@ -27,6 +27,7 @@
 #include "access/heapam.h"
 #include "access/reloptions.h"
 #include "access/htup_details.h"
+#include "access/tableam.h"
 #include "access/sysattr.h"
 #include "access/xact.h"
 #include "access/xlog.h"
@@ -572,25 +573,24 @@ static bool
 intorel_receive(TupleTableSlot *slot, DestReceiver *self)
 {
 	DR_intorel *myState = (DR_intorel *) self;
-	HeapTuple	tuple;
 
 	/*
-	 * get the heap tuple out of the tuple table slot, making sure we have a
-	 * writable copy
+	 * Note that the input slot might not be of the type of the target
+	 * relation. That's supported by table_insert(), but slightly less
+	 * efficient than inserting with the right slot - but the alternative
+	 * would be to copy into a slot of the right type, which would not be
+	 * cheap either. This also doesn't allow accessing per-AM data (say a
+	 * tuple's xmin), but since we don't do that here...
 	 */
-	tuple = ExecCopySlotHeapTuple(slot);
 
-	heap_insert(myState->rel,
-				tuple,
-				myState->output_cid,
-				myState->hi_options,
-				myState->bistate);
+	table_insert(myState->rel,
+				 slot,
+				 myState->output_cid,
+				 myState->hi_options,
+				 myState->bistate);
 
 	/* We know this is a newly created relation, so there are no indexes */
 
-	/* Free the copied tuple. */
-	heap_freetuple(tuple);
-
 	return true;
 }