Save a few cycles in EXPLAIN and related commands by not bothering to form

a physical tuple in do_tup_output().  A virtual tuple is easier to set up
and also easier for most tuple receivers to process.  Per my comment on
Robert Haas' recent patch in this code.

diff --git a/src/backend/executor/execTuples.c b/src/backend/executor/execTuples.c
index 598ef503b7b46d3011dd8af8298d77747d0eecfc..c983066307834609cb4de6dfd68aa081a5b7bbd4 100644 (file)
--- a/src/backend/executor/execTuples.c
+++ b/src/backend/executor/execTuples.c
@@ -1215,27 +1215,28 @@ begin_tup_output_tupdesc(DestReceiver *dest, TupleDesc tupdesc)
 
 /*
  * write a single tuple
- *
- * XXX This could be made more efficient, since in reality we probably only
- * need a virtual tuple.
  */
 void
 do_tup_output(TupOutputState *tstate, Datum *values, bool *isnull)
 {
-       TupleDesc       tupdesc = tstate->slot->tts_tupleDescriptor;
-       HeapTuple       tuple;
+       TupleTableSlot *slot = tstate->slot;
+       int                     natts = slot->tts_tupleDescriptor->natts;
 
-       /* form a tuple */
-       tuple = heap_form_tuple(tupdesc, values, isnull);
+       /* make sure the slot is clear */
+       ExecClearTuple(slot);
 
-       /* put it in a slot */
-       ExecStoreTuple(tuple, tstate->slot, InvalidBuffer, true);
+       /* insert data */
+       memcpy(slot->tts_values, values, natts * sizeof(Datum));
+       memcpy(slot->tts_isnull, isnull, natts * sizeof(bool));
+
+       /* mark slot as containing a virtual tuple */
+       ExecStoreVirtualTuple(slot);
 
        /* send the tuple to the receiver */
-       (*tstate->dest->receiveSlot) (tstate->slot, tstate->dest);
+       (*tstate->dest->receiveSlot) (slot, tstate->dest);
 
        /* clean up */
-       ExecClearTuple(tstate->slot);
+       ExecClearTuple(slot);
 }
 
 /*