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, 6 insertions, 28 deletions

diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 22ab5a4329f..cfc135c7beb 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -126,7 +126,6 @@ static int	namefastcmp_c(Datum x, Datum y, SortSupport ssup);
 static int	varlenafastcmp_locale(Datum x, Datum y, SortSupport ssup);
 static int	namefastcmp_locale(Datum x, Datum y, SortSupport ssup);
 static int	varstrfastcmp_locale(char *a1p, int len1, char *a2p, int len2, SortSupport ssup);
-static int	varstrcmp_abbrev(Datum x, Datum y, SortSupport ssup);
 static Datum varstr_abbrev_convert(Datum original, SortSupport ssup);
 static bool varstr_abbrev_abort(int memtupcount, SortSupport ssup);
 static int32 text_length(Datum str);
@@ -2159,7 +2158,7 @@ varstr_sortsupport(SortSupport ssup, Oid typid, Oid collid)
 			initHyperLogLog(&sss->abbr_card, 10);
 			initHyperLogLog(&sss->full_card, 10);
 			ssup->abbrev_full_comparator = ssup->comparator;
-			ssup->comparator = varstrcmp_abbrev;
+			ssup->comparator = ssup_datum_unsigned_cmp;
 			ssup->abbrev_converter = varstr_abbrev_convert;
 			ssup->abbrev_abort = varstr_abbrev_abort;
 		}
@@ -2446,27 +2445,6 @@ varstrfastcmp_locale(char *a1p, int len1, char *a2p, int len2, SortSupport ssup)
 }
 
 /*
- * Abbreviated key comparison func
- */
-static int
-varstrcmp_abbrev(Datum x, Datum y, SortSupport ssup)
-{
-	/*
-	 * When 0 is returned, the core system will call varstrfastcmp_c()
-	 * (bpcharfastcmp_c() in BpChar case) or varlenafastcmp_locale().  Even a
-	 * strcmp() on two non-truncated strxfrm() blobs cannot indicate *equality*
-	 * authoritatively, for the same reason that there is a strcoll()
-	 * tie-breaker call to strcmp() in varstr_cmp().
-	 */
-	if (x > y)
-		return 1;
-	else if (x == y)
-		return 0;
-	else
-		return -1;
-}
-
-/*
  * Conversion routine for sortsupport.  Converts original to abbreviated key
  * representation.  Our encoding strategy is simple -- pack the first 8 bytes
  * of a strxfrm() blob into a Datum (on little-endian machines, the 8 bytes are
@@ -2504,7 +2482,7 @@ varstr_abbrev_convert(Datum original, SortSupport ssup)
 	 * strings may contain NUL bytes.  Besides, this should be faster, too.
 	 *
 	 * More generally, it's okay that bytea callers can have NUL bytes in
-	 * strings because varstrcmp_abbrev() need not make a distinction between
+	 * strings because abbreviated cmp need not make a distinction between
 	 * terminating NUL bytes, and NUL bytes representing actual NULs in the
 	 * authoritative representation.  Hopefully a comparison at or past one
 	 * abbreviated key's terminating NUL byte will resolve the comparison
@@ -2694,10 +2672,10 @@ done:
 	/*
 	 * Byteswap on little-endian machines.
 	 *
-	 * This is needed so that varstrcmp_abbrev() (an unsigned integer 3-way
-	 * comparator) works correctly on all platforms.  If we didn't do this,
-	 * the comparator would have to call memcmp() with a pair of pointers to
-	 * the first byte of each abbreviated key, which is slower.
+	 * This is needed so that ssup_datum_unsigned_cmp() (an unsigned integer
+	 * 3-way comparator) works correctly on all platforms.  If we didn't do
+	 * this, the comparator would have to call memcmp() with a pair of pointers
+	 * to the first byte of each abbreviated key, which is slower.
 	 */
 	res = DatumBigEndianToNative(res);