Use virtual tuples in row-by-row fetcher

We needlessly form/deform the heap tuples currently. Sometimes we do
need this when we have row marks and need a ctid (UPDATE RETURNING),
but not in this case. The implementation has three parts:

1. Change data fetcher interface to store a tuple into given slot
instead of returning a heap tuple.

2. Expose the creation of virtual tuple in tuple factory.

3. Use these facilities in row-by-row fetcher.

This gives some small speedup. It will become more important in the
future, as other parts of row-by-row fetcher are optimized.

tsl/src/fdw/scan_exec.c

@@ -283,23 +283,12 @@ TupleTableSlot *
 fdw_scan_iterate(ScanState *ss, TsFdwScanState *fsstate)
 {
 	TupleTableSlot *slot = ss->ss_ScanTupleSlot;
-	HeapTuple tuple;
 	DataFetcher *fetcher = fsstate->fetcher;
 
 	if (NULL == fetcher)
 		fetcher = create_data_fetcher(ss, fsstate);
 
-	tuple = fetcher->funcs->get_next_tuple(fetcher);
-
-	if (NULL == tuple)
-		return ExecClearTuple(slot);
-
-	/*
-	 * Return the next tuple. Must force the tuple into the slot since
-	 * CustomScan initializes ss_ScanTupleSlot to a VirtualTupleTableSlot
-	 * while we're storing a HeapTuple.
-	 */
-	ExecForceStoreHeapTuple(tuple, slot, false);
+	fetcher->funcs->store_next_tuple(fetcher, slot);
 
 	return slot;
 }

tsl/src/remote/cursor_fetcher.c

@@ -50,8 +50,7 @@ static void cursor_fetcher_send_fetch_request(DataFetcher *df);
 static int cursor_fetcher_fetch_data(DataFetcher *df);
 static void cursor_fetcher_set_fetch_size(DataFetcher *df, int fetch_size);
 static void cursor_fetcher_set_tuple_memcontext(DataFetcher *df, MemoryContext mctx);
-static HeapTuple cursor_fetcher_get_next_tuple(DataFetcher *df);
-static HeapTuple cursor_fetcher_get_tuple(DataFetcher *df, int row);
+static void cursor_fetcher_store_next_tuple(DataFetcher *df, TupleTableSlot *slot);
 static void cursor_fetcher_rewind(DataFetcher *df);
 static void cursor_fetcher_close(DataFetcher *df);
 
@@ -60,8 +59,7 @@ static DataFetcherFuncs funcs = {
 	.fetch_data = cursor_fetcher_fetch_data,
 	.set_fetch_size = cursor_fetcher_set_fetch_size,
 	.set_tuple_mctx = cursor_fetcher_set_tuple_memcontext,
-	.get_next_tuple = cursor_fetcher_get_next_tuple,
-	.get_tuple = cursor_fetcher_get_tuple,
+	.store_next_tuple = cursor_fetcher_store_next_tuple,
 	.rewind = cursor_fetcher_rewind,
 	.close = cursor_fetcher_close,
 };
@@ -384,20 +382,12 @@ cursor_fetcher_fetch_data(DataFetcher *df)
 	return cursor_fetcher_fetch_data_complete(cursor);
 }
 
-static HeapTuple
-cursor_fetcher_get_tuple(DataFetcher *df, int row)
+static void
+cursor_fetcher_store_next_tuple(DataFetcher *df, TupleTableSlot *slot)
 {
 	CursorFetcher *cursor = cast_fetcher(CursorFetcher, df);
 
-	return data_fetcher_get_tuple(&cursor->state, row);
-}
-
-static HeapTuple
-cursor_fetcher_get_next_tuple(DataFetcher *df)
-{
-	CursorFetcher *cursor = cast_fetcher(CursorFetcher, df);
-
-	return data_fetcher_get_next_tuple(&cursor->state);
+	data_fetcher_store_next_tuple(&cursor->state, slot);
 }
 
 static void

tsl/src/remote/data_fetcher.c

@@ -51,14 +51,17 @@ data_fetcher_validate(DataFetcher *df)
 				 errhint("Shouldn't fetch new data before consuming existing.")));
 }
 
-HeapTuple
-data_fetcher_get_tuple(DataFetcher *df, int row)
+void
+data_fetcher_store_tuple(DataFetcher *df, int row, TupleTableSlot *slot)
 {
 	if (row >= df->num_tuples)
 	{
 		/* No point in another fetch if we already detected EOF, though. */
 		if (df->eof || df->funcs->fetch_data(df) == 0)
-			return NULL;
+		{
+			ExecClearTuple(slot);
+			return;
+		}
 
 		/* More data was fetched so need to reset row index */
 		row = 0;
@@ -68,20 +71,23 @@ data_fetcher_get_tuple(DataFetcher *df, int row)
 	Assert(df->tuples != NULL);
 	Assert(row >= 0 && row < df->num_tuples);
 
-	return df->tuples[row];
+	/*
+	 * Return the next tuple. Must force the tuple into the slot since
+	 * CustomScan initializes ss_ScanTupleSlot to a VirtualTupleTableSlot
+	 * while we're storing a HeapTuple.
+	 */
+	ExecForceStoreHeapTuple(df->tuples[row], slot, /* shouldFree = */ false);
 }
 
-HeapTuple
-data_fetcher_get_next_tuple(DataFetcher *df)
+void
+data_fetcher_store_next_tuple(DataFetcher *df, TupleTableSlot *slot)
 {
-	HeapTuple tuple = data_fetcher_get_tuple(df, df->next_tuple_idx);
+	data_fetcher_store_tuple(df, df->next_tuple_idx, slot);
 
-	if (tuple != NULL)
+	if (!TupIsNull(slot))
 		df->next_tuple_idx++;
 
 	Assert(df->next_tuple_idx <= df->num_tuples);
-
-	return tuple;
 }
 
 void

tsl/src/remote/data_fetcher.h

@@ -28,8 +28,7 @@ typedef struct DataFetcherFuncs
 	/* Set the fetch (batch) size */
 	void (*set_fetch_size)(DataFetcher *data_fetcher, int fetch_size);
 	void (*set_tuple_mctx)(DataFetcher *data_fetcher, MemoryContext mctx);
-	HeapTuple (*get_next_tuple)(DataFetcher *data_fetcher);
-	HeapTuple (*get_tuple)(DataFetcher *data_fetcher, int row);
+	void (*store_next_tuple)(DataFetcher *data_fetcher, TupleTableSlot *slot);
 	void (*rewind)(DataFetcher *data_fetcher);
 	void (*close)(DataFetcher *data_fetcher);
 } DataFetcherFuncs;
@@ -67,8 +66,8 @@ extern void data_fetcher_init(DataFetcher *df, TSConnection *conn, const char *s
 							  StmtParams *params, Relation rel, ScanState *ss,
 							  List *retrieved_attrs);
 
-extern HeapTuple data_fetcher_get_tuple(DataFetcher *df, int row);
-extern HeapTuple data_fetcher_get_next_tuple(DataFetcher *df);
+extern void data_fetcher_store_tuple(DataFetcher *df, int row, TupleTableSlot *slot);
+extern void data_fetcher_store_next_tuple(DataFetcher *df, TupleTableSlot *slot);
 extern void data_fetcher_set_fetch_size(DataFetcher *df, int fetch_size);
 extern void data_fetcher_set_tuple_mctx(DataFetcher *df, MemoryContext mctx);
 extern void data_fetcher_validate(DataFetcher *df);

tsl/src/remote/row_by_row_fetcher.c

@@ -13,6 +13,10 @@
 typedef struct RowByRowFetcher
 {
 	DataFetcher state;
+
+	/* Data for virtual tuples of the current retrieved batch. */
+	Datum *batch_values;
+	bool *batch_nulls;
 } RowByRowFetcher;
 
 static void row_by_row_fetcher_send_fetch_request(DataFetcher *df);
@@ -20,8 +24,7 @@ static void row_by_row_fetcher_reset(RowByRowFetcher *fetcher);
 static int row_by_row_fetcher_fetch_data(DataFetcher *df);
 static void row_by_row_fetcher_set_fetch_size(DataFetcher *df, int fetch_size);
 static void row_by_row_fetcher_set_tuple_memcontext(DataFetcher *df, MemoryContext mctx);
-static HeapTuple row_by_row_fetcher_get_next_tuple(DataFetcher *df);
-static HeapTuple row_by_row_fetcher_get_tuple(DataFetcher *df, int row);
+static void row_by_row_fetcher_store_next_tuple(DataFetcher *df, TupleTableSlot *slot);
 static void row_by_row_fetcher_rescan(DataFetcher *df);
 static void row_by_row_fetcher_close(DataFetcher *df);
 
@@ -30,8 +33,7 @@ static DataFetcherFuncs funcs = {
 	.fetch_data = row_by_row_fetcher_fetch_data,
 	.set_fetch_size = row_by_row_fetcher_set_fetch_size,
 	.set_tuple_mctx = row_by_row_fetcher_set_tuple_memcontext,
-	.get_next_tuple = row_by_row_fetcher_get_next_tuple,
-	.get_tuple = row_by_row_fetcher_get_tuple,
+	.store_next_tuple = row_by_row_fetcher_store_next_tuple,
 	.rewind = row_by_row_fetcher_rescan,
 	.close = row_by_row_fetcher_close,
 };
@@ -149,7 +151,14 @@ row_by_row_fetcher_complete(RowByRowFetcher *fetcher)
 	 */
 	MemoryContextReset(fetcher->state.batch_mctx);
 	oldcontext = MemoryContextSwitchTo(fetcher->state.batch_mctx);
-	fetcher->state.tuples = palloc0(fetcher->state.fetch_size * sizeof(HeapTuple));
+	const int nattrs = tuplefactory_get_nattrs(fetcher->state.tf);
+	const int total = nattrs * fetcher->state.fetch_size;
+	fetcher->batch_nulls = palloc(sizeof(bool) * total);
+	for (int i = 0; i < total; i++)
+	{
+		fetcher->batch_nulls[i] = true;
+	}
+	fetcher->batch_values = palloc0(sizeof(Datum) * total);
 
 	PG_TRY();
 	{
@@ -199,8 +208,19 @@ row_by_row_fetcher_complete(RowByRowFetcher *fetcher)
 			 * it explicitly, otherwise same as batch_mctx */
 			MemoryContextSwitchTo(fetcher->state.tuple_mctx);
 
-			fetcher->state.tuples[i] =
-				tuplefactory_make_tuple(fetcher->state.tf, res, 0, PQbinaryTuples(res));
+			PG_USED_FOR_ASSERTS_ONLY ItemPointer ctid =
+				tuplefactory_make_virtual_tuple(fetcher->state.tf,
+												res,
+												0,
+												PQbinaryTuples(res),
+												&fetcher->batch_values[i * nattrs],
+												&fetcher->batch_nulls[i * nattrs]);
+
+			/*
+			 * This fetcher uses virtual tuples that can't hold ctid, so if we're
+			 * receiving a ctid here, we're doing something wrong.
+			 */
+			Assert(ctid == NULL);
 
 			async_response_result_close(response);
 			response = NULL;
@@ -259,20 +279,43 @@ row_by_row_fetcher_fetch_data(DataFetcher *df)
 	return row_by_row_fetcher_complete(fetcher);
 }
 
-static HeapTuple
-row_by_row_fetcher_get_tuple(DataFetcher *df, int row)
+static void
+row_by_row_fetcher_store_tuple(DataFetcher *df, int row, TupleTableSlot *slot)
 {
 	RowByRowFetcher *fetcher = cast_fetcher(RowByRowFetcher, df);
 
-	return data_fetcher_get_tuple(&fetcher->state, row);
+	ExecClearTuple(slot);
+
+	if (row >= df->num_tuples)
+	{
+		if (df->eof || df->funcs->fetch_data(df) == 0)
+		{
+			return;
+		}
+
+		row = 0;
+		Assert(row == df->next_tuple_idx);
+	}
+
+	Assert(fetcher->batch_values != NULL);
+	Assert(fetcher->batch_nulls != NULL);
+	Assert(row >= 0 && row < df->num_tuples);
+
+	const int nattrs = tuplefactory_get_nattrs(fetcher->state.tf);
+	slot->tts_values = &fetcher->batch_values[nattrs * row];
+	slot->tts_isnull = &fetcher->batch_nulls[nattrs * row];
+	ExecStoreVirtualTuple(slot);
 }
 
-static HeapTuple
-row_by_row_fetcher_get_next_tuple(DataFetcher *df)
+static void
+row_by_row_fetcher_store_next_tuple(DataFetcher *df, TupleTableSlot *slot)
 {
-	RowByRowFetcher *fetcher = cast_fetcher(RowByRowFetcher, df);
+	row_by_row_fetcher_store_tuple(df, df->next_tuple_idx, slot);
 
-	return data_fetcher_get_next_tuple(&fetcher->state);
+	if (!TupIsNull(slot))
+		df->next_tuple_idx++;
+
+	Assert(df->next_tuple_idx <= df->num_tuples);
 }
 
 DataFetcher *

tsl/src/remote/tuplefactory.c

@@ -231,24 +231,23 @@ tuplefactory_reset_mctx(TupleFactory *tf)
 	MemoryContextReset(tf->temp_mctx);
 }
 
-HeapTuple
-tuplefactory_make_tuple(TupleFactory *tf, PGresult *res, int row, int format)
+int
+tuplefactory_get_nattrs(TupleFactory *tf)
+{
+	return tf->tupdesc->natts;
+}
+
+ItemPointer
+tuplefactory_make_virtual_tuple(TupleFactory *tf, PGresult *res, int row, int format, Datum *values,
+								bool *nulls)
 {
-	HeapTuple tuple;
 	ItemPointer ctid = NULL;
-	MemoryContext oldcontext;
 	ListCell *lc;
 	int j;
 	StringInfo buf;
 
 	Assert(row < PQntuples(res));
 
-	/*
-	 * Do the following work in a temp context that we reset after each tuple.
-	 * This cleans up not only the data we have direct access to, but any
-	 * cruft the I/O functions might leak.
-	 */
-	oldcontext = MemoryContextSwitchTo(tf->temp_mctx);
 	buf = makeStringInfo();
 
 	/* Install error callback */
@@ -290,27 +289,27 @@ tuplefactory_make_tuple(TupleFactory *tf, PGresult *res, int row, int format)
 		{
 			/* ordinary column */
 			Assert(i <= tf->tupdesc->natts);
-			tf->nulls[i - 1] = (valstr == NULL);
+			nulls[i - 1] = (valstr == NULL);
 
 			if (format == FORMAT_TEXT)
 			{
 				Assert(!tf->attconv->binary);
 				/* Apply the input function even to nulls, to support domains */
-				tf->values[i - 1] = InputFunctionCall(&tf->attconv->conv_funcs[i - 1],
-													  valstr,
-													  tf->attconv->ioparams[i - 1],
-													  tf->attconv->typmods[i - 1]);
+				values[i - 1] = InputFunctionCall(&tf->attconv->conv_funcs[i - 1],
+												  valstr,
+												  tf->attconv->ioparams[i - 1],
+												  tf->attconv->typmods[i - 1]);
 			}
 			else
 			{
 				Assert(tf->attconv->binary);
 				if (valstr != NULL)
-					tf->values[i - 1] = ReceiveFunctionCall(&tf->attconv->conv_funcs[i - 1],
-															buf,
-															tf->attconv->ioparams[i - 1],
-															tf->attconv->typmods[i - 1]);
+					values[i - 1] = ReceiveFunctionCall(&tf->attconv->conv_funcs[i - 1],
+														buf,
+														tf->attconv->ioparams[i - 1],
+														tf->attconv->typmods[i - 1]);
 				else
-					tf->values[i - 1] = PointerGetDatum(NULL);
+					values[i - 1] = PointerGetDatum(NULL);
 			}
 		}
 		else if (i == SelfItemPointerAttributeNumber)
@@ -341,12 +340,27 @@ tuplefactory_make_tuple(TupleFactory *tf, PGresult *res, int row, int format)
 	if (j > 0 && j != PQnfields(res))
 		elog(ERROR, "remote query result does not match the foreign table");
 
+	return ctid;
+}
+
+HeapTuple
+tuplefactory_make_tuple(TupleFactory *tf, PGresult *res, int row, int format)
+{
+	/*
+	 * Do the following work in a temp context that we reset after each tuple.
+	 * This cleans up not only the data we have direct access to, but any
+	 * cruft the I/O functions might leak.
+	 */
+	MemoryContext oldcontext = MemoryContextSwitchTo(tf->temp_mctx);
+
+	ItemPointer ctid = tuplefactory_make_virtual_tuple(tf, res, row, format, tf->values, tf->nulls);
+
 	/*
 	 * Build the result tuple in caller's memory context.
 	 */
 	MemoryContextSwitchTo(oldcontext);
 
-	tuple = heap_form_tuple(tf->tupdesc, tf->values, tf->nulls);
+	HeapTuple tuple = heap_form_tuple(tf->tupdesc, tf->values, tf->nulls);
 
 	/*
 	 * If we have a CTID to return, install it in both t_self and t_ctid.

tsl/src/remote/tuplefactory.h

@@ -21,8 +21,11 @@ extern TupleFactory *tuplefactory_create_for_tupdesc(TupleDesc tupdesc, bool for
 extern TupleFactory *tuplefactory_create_for_rel(Relation rel, List *retrieved_attrs);
 extern TupleFactory *tuplefactory_create_for_scan(ScanState *ss, List *retrieved_attrs);
 extern HeapTuple tuplefactory_make_tuple(TupleFactory *tf, PGresult *res, int row, int format);
+extern ItemPointer tuplefactory_make_virtual_tuple(TupleFactory *tf, PGresult *res, int row,
+												   int format, Datum *values, bool *nulls);
 extern bool tuplefactory_is_binary(TupleFactory *tf);
 extern void tuplefactory_set_per_tuple_mctx_reset(TupleFactory *tf, bool reset);
 extern void tuplefactory_reset_mctx(TupleFactory *tf);
+extern int tuplefactory_get_nattrs(TupleFactory *tf);
 
 #endif /* TIMESCALEDB_TSL_REMOTE_TUPLEFACTORY_H */