Reuse abbreviated keys in ordered [set] aggregates.

When processing ordered aggregates following a sort that could make use
of the abbreviated key optimization, only call the equality operator to
compare successive pairs of tuples when their abbreviated keys were not
equal.

Peter Geoghegan, reviewd by Andreas Karlsson and by me.

2 files changed, 75 insertions, 32 deletions

diff --git a/src/backend/utils/adt/orderedsetaggs.c b/src/backend/utils/adt/orderedsetaggs.c
index 57201fd03d4..fe44d561295 100644
--- a/src/backend/utils/adt/orderedsetaggs.c
+++ b/src/backend/utils/adt/orderedsetaggs.c
@@ -453,7 +453,7 @@ percentile_disc_final(PG_FUNCTION_ARGS)
 			elog(ERROR, "missing row in percentile_disc");
 	}
 
-	if (!tuplesort_getdatum(osastate->sortstate, true, &val, &isnull))
+	if (!tuplesort_getdatum(osastate->sortstate, true, &val, &isnull, NULL))
 		elog(ERROR, "missing row in percentile_disc");
 
 	/*
@@ -553,7 +553,7 @@ percentile_cont_final_common(FunctionCallInfo fcinfo,
 	if (!tuplesort_skiptuples(osastate->sortstate, first_row, true))
 		elog(ERROR, "missing row in percentile_cont");
 
-	if (!tuplesort_getdatum(osastate->sortstate, true, &first_val, &isnull))
+	if (!tuplesort_getdatum(osastate->sortstate, true, &first_val, &isnull, NULL))
 		elog(ERROR, "missing row in percentile_cont");
 	if (isnull)
 		PG_RETURN_NULL();
@@ -564,7 +564,7 @@ percentile_cont_final_common(FunctionCallInfo fcinfo,
 	}
 	else
 	{
-		if (!tuplesort_getdatum(osastate->sortstate, true, &second_val, &isnull))
+		if (!tuplesort_getdatum(osastate->sortstate, true, &second_val, &isnull, NULL))
 			elog(ERROR, "missing row in percentile_cont");
 
 		if (isnull)
@@ -792,7 +792,7 @@ percentile_disc_multi_final(PG_FUNCTION_ARGS)
 				if (!tuplesort_skiptuples(osastate->sortstate, target_row - rownum - 1, true))
 					elog(ERROR, "missing row in percentile_disc");
 
-				if (!tuplesort_getdatum(osastate->sortstate, true, &val, &isnull))
+				if (!tuplesort_getdatum(osastate->sortstate, true, &val, &isnull, NULL))
 					elog(ERROR, "missing row in percentile_disc");
 
 				rownum = target_row;
@@ -921,7 +921,8 @@ percentile_cont_multi_final_common(FunctionCallInfo fcinfo,
 				if (!tuplesort_skiptuples(osastate->sortstate, first_row - rownum - 1, true))
 					elog(ERROR, "missing row in percentile_cont");
 
-				if (!tuplesort_getdatum(osastate->sortstate, true, &first_val, &isnull) || isnull)
+				if (!tuplesort_getdatum(osastate->sortstate, true, &first_val,
+										&isnull, NULL) || isnull)
 					elog(ERROR, "missing row in percentile_cont");
 
 				rownum = first_row;
@@ -941,7 +942,8 @@ percentile_cont_multi_final_common(FunctionCallInfo fcinfo,
 			/* Fetch second_row if needed */
 			if (second_row > rownum)
 			{
-				if (!tuplesort_getdatum(osastate->sortstate, true, &second_val, &isnull) || isnull)
+				if (!tuplesort_getdatum(osastate->sortstate, true, &second_val,
+										&isnull, NULL) || isnull)
 					elog(ERROR, "missing row in percentile_cont");
 				rownum++;
 			}
@@ -1016,6 +1018,8 @@ mode_final(PG_FUNCTION_ARGS)
 	int64		last_val_freq = 0;
 	bool		last_val_is_mode = false;
 	FmgrInfo   *equalfn;
+	Datum		abbrev_val = (Datum) 0;
+	Datum		last_abbrev_val = (Datum) 0;
 	bool		shouldfree;
 
 	Assert(AggCheckCallContext(fcinfo, NULL) == AGG_CONTEXT_AGGREGATE);
@@ -1042,7 +1046,7 @@ mode_final(PG_FUNCTION_ARGS)
 	tuplesort_performsort(osastate->sortstate);
 
 	/* Scan tuples and count frequencies */
-	while (tuplesort_getdatum(osastate->sortstate, true, &val, &isnull))
+	while (tuplesort_getdatum(osastate->sortstate, true, &val, &isnull, &abbrev_val))
 	{
 		/* we don't expect any nulls, but ignore them if found */
 		if (isnull)
@@ -1054,8 +1058,10 @@ mode_final(PG_FUNCTION_ARGS)
 			mode_val = last_val = val;
 			mode_freq = last_val_freq = 1;
 			last_val_is_mode = true;
+			last_abbrev_val = abbrev_val;
 		}
-		else if (DatumGetBool(FunctionCall2(equalfn, val, last_val)))
+		else if (abbrev_val == last_abbrev_val &&
+				 DatumGetBool(FunctionCall2(equalfn, val, last_val)))
 		{
 			/* value equal to previous value, count it */
 			if (last_val_is_mode)
@@ -1078,6 +1084,8 @@ mode_final(PG_FUNCTION_ARGS)
 			if (shouldfree && !last_val_is_mode)
 				pfree(DatumGetPointer(last_val));
 			last_val = val;
+			/* avoid equality function calls by reusing abbreviated keys */
+			last_abbrev_val = abbrev_val;
 			last_val_freq = 1;
 			last_val_is_mode = false;
 		}
@@ -1181,7 +1189,7 @@ hypothetical_rank_common(FunctionCallInfo fcinfo, int flag,
 	tuplesort_performsort(osastate->sortstate);
 
 	/* iterate till we find the hypothetical row */
-	while (tuplesort_gettupleslot(osastate->sortstate, true, slot))
+	while (tuplesort_gettupleslot(osastate->sortstate, true, slot, NULL))
 	{
 		bool		isnull;
 		Datum		d = slot_getattr(slot, nargs + 1, &isnull);
@@ -1266,6 +1274,8 @@ hypothetical_dense_rank_final(PG_FUNCTION_ARGS)
 	int64		duplicate_count = 0;
 	OSAPerGroupState *osastate;
 	int			numDistinctCols;
+	Datum		abbrevVal = (Datum) 0;
+	Datum		abbrevOld = (Datum) 0;
 	AttrNumber *sortColIdx;
 	FmgrInfo   *equalfns;
 	TupleTableSlot *slot;
@@ -1342,7 +1352,7 @@ hypothetical_dense_rank_final(PG_FUNCTION_ARGS)
 	slot2 = extraslot;
 
 	/* iterate till we find the hypothetical row */
-	while (tuplesort_gettupleslot(osastate->sortstate, true, slot))
+	while (tuplesort_gettupleslot(osastate->sortstate, true, slot, &abbrevVal))
 	{
 		bool		isnull;
 		Datum		d = slot_getattr(slot, nargs + 1, &isnull);
@@ -1353,6 +1363,7 @@ hypothetical_dense_rank_final(PG_FUNCTION_ARGS)
 
 		/* count non-distinct tuples */
 		if (!TupIsNull(slot2) &&
+			abbrevVal == abbrevOld &&
 			execTuplesMatch(slot, slot2,
 							numDistinctCols,
 							sortColIdx,
@@ -1363,6 +1374,8 @@ hypothetical_dense_rank_final(PG_FUNCTION_ARGS)
 		tmpslot = slot2;
 		slot2 = slot;
 		slot = tmpslot;
+		/* avoid execTuplesMatch() calls by reusing abbreviated keys */
+		abbrevOld = abbrevVal;
 
 		rank++;
 
diff --git a/src/backend/utils/sort/tuplesort.c b/src/backend/utils/sort/tuplesort.c
index a30e1707a79..67d86ed83b4 100644
--- a/src/backend/utils/sort/tuplesort.c
+++ b/src/backend/utils/sort/tuplesort.c
@@ -1280,7 +1280,8 @@ tuplesort_putindextuplevalues(Tuplesortstate *state, Relation rel,
 		 * converter it won't expect NULL values, and cost model is not
 		 * required to account for NULL, so in that case we avoid calling
 		 * converter and just set datum1 to zeroed representation (to be
-		 * consistent).
+		 * consistent, and to support cheap inequality tests for NULL
+		 * abbreviated keys).
 		 */
 		stup.datum1 = original;
 	}
@@ -1349,7 +1350,11 @@ tuplesort_putdatum(Tuplesortstate *state, Datum val, bool isNull)
 
 	if (isNull || state->datumTypeByVal)
 	{
-		stup.datum1 = val;
+		/*
+		 * Set datum1 to zeroed representation for NULLs (to be consistent, and
+		 * to support cheap inequality tests for NULL abbreviated keys).
+		 */
+		stup.datum1 = !isNull ? val : (Datum) 0;
 		stup.isnull1 = isNull;
 		stup.tuple = NULL;		/* no separate storage */
 	}
@@ -1866,10 +1871,17 @@ tuplesort_gettuple_common(Tuplesortstate *state, bool forward,
  * Fetch the next tuple in either forward or back direction.
  * If successful, put tuple in slot and return TRUE; else, clear the slot
  * and return FALSE.
+ *
+ * Caller may optionally be passed back abbreviated value (on TRUE return
+ * value) when abbreviation was used, which can be used to cheaply avoid
+ * equality checks that might otherwise be required.  Caller can safely make a
+ * determination of "non-equal tuple" based on simple binary inequality.  A
+ * NULL value in leading attribute will set abbreviated value to zeroed
+ * representation, which caller may rely on in abbreviated inequality check.
  */
 bool
 tuplesort_gettupleslot(Tuplesortstate *state, bool forward,
-					   TupleTableSlot *slot)
+					   TupleTableSlot *slot, Datum *abbrev)
 {
 	MemoryContext oldcontext = MemoryContextSwitchTo(state->sortcontext);
 	SortTuple	stup;
@@ -1882,6 +1894,10 @@ tuplesort_gettupleslot(Tuplesortstate *state, bool forward,
 
 	if (stup.tuple)
 	{
+		/* Record abbreviated key for caller */
+		if (state->sortKeys->abbrev_converter && abbrev)
+			*abbrev = stup.datum1;
+
 		ExecStoreMinimalTuple((MinimalTuple) stup.tuple, slot, should_free);
 		return true;
 	}
@@ -1937,10 +1953,17 @@ tuplesort_getindextuple(Tuplesortstate *state, bool forward,
  *
  * If the Datum is pass-by-ref type, the returned value is freshly palloc'd
  * and is now owned by the caller.
+ *
+ * Caller may optionally be passed back abbreviated value (on TRUE return
+ * value) when abbreviation was used, which can be used to cheaply avoid
+ * equality checks that might otherwise be required.  Caller can safely make a
+ * determination of "non-equal tuple" based on simple binary inequality.  A
+ * NULL value will have a zeroed abbreviated value representation, which caller
+ * may rely on in abbreviated inequality check.
  */
 bool
 tuplesort_getdatum(Tuplesortstate *state, bool forward,
-				   Datum *val, bool *isNull)
+				   Datum *val, bool *isNull, Datum *abbrev)
 {
 	MemoryContext oldcontext = MemoryContextSwitchTo(state->sortcontext);
 	SortTuple	stup;
@@ -1952,6 +1975,10 @@ tuplesort_getdatum(Tuplesortstate *state, bool forward,
 		return false;
 	}
 
+	/* Record abbreviated key for caller */
+	if (state->sortKeys->abbrev_converter && abbrev)
+		*abbrev = stup.datum1;
+
 	if (stup.isnull1 || state->datumTypeByVal)
 	{
 		*val = stup.datum1;
@@ -2232,21 +2259,6 @@ mergeruns(Tuplesortstate *state)
 	Assert(state->status == TSS_BUILDRUNS);
 	Assert(state->memtupcount == 0);
 
-	/*
-	 * If we produced only one initial run (quite likely if the total data
-	 * volume is between 1X and 2X workMem), we can just use that tape as the
-	 * finished output, rather than doing a useless merge.  (This obvious
-	 * optimization is not in Knuth's algorithm.)
-	 */
-	if (state->currentRun == 1)
-	{
-		state->result_tape = state->tp_tapenum[state->destTape];
-		/* must freeze and rewind the finished output tape */
-		LogicalTapeFreeze(state->tapeset, state->result_tape);
-		state->status = TSS_SORTEDONTAPE;
-		return;
-	}
-
 	if (state->sortKeys != NULL && state->sortKeys->abbrev_converter != NULL)
 	{
 		/*
@@ -2263,6 +2275,21 @@ mergeruns(Tuplesortstate *state)
 		state->sortKeys->abbrev_full_comparator = NULL;
 	}
 
+	/*
+	 * If we produced only one initial run (quite likely if the total data
+	 * volume is between 1X and 2X workMem), we can just use that tape as the
+	 * finished output, rather than doing a useless merge.  (This obvious
+	 * optimization is not in Knuth's algorithm.)
+	 */
+	if (state->currentRun == 1)
+	{
+		state->result_tape = state->tp_tapenum[state->destTape];
+		/* must freeze and rewind the finished output tape */
+		LogicalTapeFreeze(state->tapeset, state->result_tape);
+		state->status = TSS_SORTEDONTAPE;
+		return;
+	}
+
 	/* End of step D2: rewind all output tapes to prepare for merging */
 	for (tapenum = 0; tapenum < state->tapeRange; tapenum++)
 		LogicalTapeRewind(state->tapeset, tapenum, false);
@@ -3164,7 +3191,8 @@ copytup_heap(Tuplesortstate *state, SortTuple *stup, void *tup)
 		 * converter it won't expect NULL values, and cost model is not
 		 * required to account for NULL, so in that case we avoid calling
 		 * converter and just set datum1 to zeroed representation (to be
-		 * consistent).
+		 * consistent, and to support cheap inequality tests for NULL
+		 * abbreviated keys).
 		 */
 		stup->datum1 = original;
 	}
@@ -3406,7 +3434,8 @@ copytup_cluster(Tuplesortstate *state, SortTuple *stup, void *tup)
 		 * converter it won't expect NULL values, and cost model is not
 		 * required to account for NULL, so in that case we avoid calling
 		 * converter and just set datum1 to zeroed representation (to be
-		 * consistent).
+		 * consistent, and to support cheap inequality tests for NULL
+		 * abbreviated keys).
 		 */
 		stup->datum1 = original;
 	}
@@ -3710,7 +3739,8 @@ copytup_index(Tuplesortstate *state, SortTuple *stup, void *tup)
 		 * converter it won't expect NULL values, and cost model is not
 		 * required to account for NULL, so in that case we avoid calling
 		 * converter and just set datum1 to zeroed representation (to be
-		 * consistent).
+		 * consistent, and to support cheap inequality tests for NULL
+		 * abbreviated keys).
 		 */
 		stup->datum1 = original;
 	}