Specialize tuplesort routines for different kinds of abbreviated keys

Previously, the specialized tuplesort routine inlined handling for
reverse-sort and NULLs-ordering but called the datum comparator via a
pointer in the SortSupport struct parameter. Testing has showed that we
can get a useful performance gain by specializing datum comparison for
the different representations of abbreviated keys -- signed and unsigned
64-bit integers and signed 32-bit integers. Almost all abbreviatable data
types will benefit -- the only exception for now is numeric, since the
datum comparison is more complex. The performance gain depends on data
type and input distribution, but often falls in the range of 10-20% faster.

Thomas Munro

Reviewed by Peter Geoghegan, review and performance testing by me

Discussion:
https://www.postgresql.org/message-id/CA%2BhUKGKKYttZZk-JMRQSVak%3DCXSJ5fiwtirFf%3Dn%3DPAbumvn1Ww%40mail.gmail.com

1 files changed, 3 insertions, 20 deletions

diff --git a/src/backend/utils/adt/mac.c b/src/backend/utils/adt/mac.c
index 88a1698cf96..ac7342cfca7 100644
--- a/src/backend/utils/adt/mac.c
+++ b/src/backend/utils/adt/mac.c
@@ -44,7 +44,6 @@ typedef struct
 
 static int	macaddr_cmp_internal(macaddr *a1, macaddr *a2);
 static int	macaddr_fast_cmp(Datum x, Datum y, SortSupport ssup);
-static int	macaddr_cmp_abbrev(Datum x, Datum y, SortSupport ssup);
 static bool macaddr_abbrev_abort(int memtupcount, SortSupport ssup);
 static Datum macaddr_abbrev_convert(Datum original, SortSupport ssup);
 
@@ -381,7 +380,7 @@ macaddr_sortsupport(PG_FUNCTION_ARGS)
 
 		ssup->ssup_extra = uss;
 
-		ssup->comparator = macaddr_cmp_abbrev;
+		ssup->comparator = ssup_datum_unsigned_cmp;
 		ssup->abbrev_converter = macaddr_abbrev_convert;
 		ssup->abbrev_abort = macaddr_abbrev_abort;
 		ssup->abbrev_full_comparator = macaddr_fast_cmp;
@@ -406,22 +405,6 @@ macaddr_fast_cmp(Datum x, Datum y, SortSupport ssup)
 }
 
 /*
- * SortSupport abbreviated key comparison function. Compares two MAC addresses
- * quickly by treating them like integers, and without having to go to the
- * heap.
- */
-static int
-macaddr_cmp_abbrev(Datum x, Datum y, SortSupport ssup)
-{
-	if (x > y)
-		return 1;
-	else if (x == y)
-		return 0;
-	else
-		return -1;
-}
-
-/*
  * Callback for estimating effectiveness of abbreviated key optimization.
  *
  * We pay no attention to the cardinality of the non-abbreviated data, because
@@ -537,8 +520,8 @@ macaddr_abbrev_convert(Datum original, SortSupport ssup)
 	/*
 	 * Byteswap on little-endian machines.
 	 *
-	 * This is needed so that macaddr_cmp_abbrev() (an unsigned integer 3-way
-	 * comparator) works correctly on all platforms. Without this, the
+	 * This is needed so that ssup_datum_unsigned_cmp() (an unsigned integer
+	 * 3-way comparator) works correctly on all platforms. Without this, the
 	 * comparator would have to call memcmp() with a pair of pointers to the
 	 * first byte of each abbreviated key, which is slower.
 	 */