From 8205258fa675115439017b626c4932d5fefe2ea8 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 9 Feb 2009 21:18:28 +0000
Subject: [PATCH] Adopt Bob Jenkins' improved hash function for hash_any().
This changes the contents of hash indexes (again), so bump catversion.
Kenneth Marshall
---
src/backend/access/hash/hashfunc.c | 116 +++++++++++++++------
src/include/catalog/catversion.h | 4 +-
src/test/regress/expected/polymorphism.out | 92 ++++++++--------
src/test/regress/expected/union.out | 16 +--
src/test/regress/sql/polymorphism.sql | 46 ++++----
5 files changed, 163 insertions(+), 111 deletions(-)
diff --git a/src/backend/access/hash/hashfunc.c b/src/backend/access/hash/hashfunc.c
index 3d5eef7c151..4561a09481d 100644
--- a/src/backend/access/hash/hashfunc.c
+++ b/src/backend/access/hash/hashfunc.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/hash/hashfunc.c,v 1.57 2009/01/01 17:23:35 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/hash/hashfunc.c,v 1.58 2009/02/09 21:18:28 tgl Exp $
*
* NOTES
* These functions are stored in pg_amproc. For each operator class
@@ -200,39 +200,95 @@ hashvarlena(PG_FUNCTION_ARGS)
* hash function, see http://burtleburtle.net/bob/hash/doobs.html,
* or Bob's article in Dr. Dobb's Journal, Sept. 1997.
*
- * In the current code, we have adopted an idea from Bob's 2006 update
- * of his hash function, which is to fetch the data a word at a time when
- * it is suitably aligned. This makes for a useful speedup, at the cost
- * of having to maintain four code paths (aligned vs unaligned, and
- * little-endian vs big-endian). Note that we have NOT adopted his newer
- * mix() function, which is faster but may sacrifice some randomness.
+ * In the current code, we have adopted Bob's 2006 update of his hash
+ * function to fetch the data a word at a time when it is suitably aligned.
+ * This makes for a useful speedup, at the cost of having to maintain
+ * four code paths (aligned vs unaligned, and little-endian vs big-endian).
+ * It also uses two separate mixing functions mix() and final(), instead
+ * of a slower multi-purpose function.
*/
/* Get a bit mask of the bits set in non-uint32 aligned addresses */
#define UINT32_ALIGN_MASK (sizeof(uint32) - 1)
+/* Rotate a uint32 value left by k bits - note multiple evaluation! */
+#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
+
/*----------
* mix -- mix 3 32-bit values reversibly.
- * For every delta with one or two bits set, and the deltas of all three
- * high bits or all three low bits, whether the original value of a,b,c
- * is almost all zero or is uniformly distributed,
- * - If mix() is run forward or backward, at least 32 bits in a,b,c
- * have at least 1/4 probability of changing.
- * - If mix() is run forward, every bit of c will change between 1/3 and
- * 2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.)
+ *
+ * This is reversible, so any information in (a,b,c) before mix() is
+ * still in (a,b,c) after mix().
+ *
+ * If four pairs of (a,b,c) inputs are run through mix(), or through
+ * mix() in reverse, there are at least 32 bits of the output that
+ * are sometimes the same for one pair and different for another pair.
+ * This was tested for:
+ * * pairs that differed by one bit, by two bits, in any combination
+ * of top bits of (a,b,c), or in any combination of bottom bits of
+ * (a,b,c).
+ * * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
+ * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
+ * is commonly produced by subtraction) look like a single 1-bit
+ * difference.
+ * * the base values were pseudorandom, all zero but one bit set, or
+ * all zero plus a counter that starts at zero.
+ *
+ * This does not achieve avalanche. There are input bits of (a,b,c)
+ * that fail to affect some output bits of (a,b,c), especially of a. The
+ * most thoroughly mixed value is c, but it doesn't really even achieve
+ * avalanche in c.
+ *
+ * This allows some parallelism. Read-after-writes are good at doubling
+ * the number of bits affected, so the goal of mixing pulls in the opposite
+ * direction from the goal of parallelism. I did what I could. Rotates
+ * seem to cost as much as shifts on every machine I could lay my hands on,
+ * and rotates are much kinder to the top and bottom bits, so I used rotates.
*----------
*/
#define mix(a,b,c) \
{ \
- a -= b; a -= c; a ^= ((c)>>13); \
- b -= c; b -= a; b ^= ((a)<<8); \
- c -= a; c -= b; c ^= ((b)>>13); \
- a -= b; a -= c; a ^= ((c)>>12); \
- b -= c; b -= a; b ^= ((a)<<16); \
- c -= a; c -= b; c ^= ((b)>>5); \
- a -= b; a -= c; a ^= ((c)>>3); \
- b -= c; b -= a; b ^= ((a)<<10); \
- c -= a; c -= b; c ^= ((b)>>15); \
+ a -= c; a ^= rot(c, 4); c += b; \
+ b -= a; b ^= rot(a, 6); a += c; \
+ c -= b; c ^= rot(b, 8); b += a; \
+ a -= c; a ^= rot(c,16); c += b; \
+ b -= a; b ^= rot(a,19); a += c; \
+ c -= b; c ^= rot(b, 4); b += a; \
+}
+
+/*----------
+ * final -- final mixing of 3 32-bit values (a,b,c) into c
+ *
+ * Pairs of (a,b,c) values differing in only a few bits will usually
+ * produce values of c that look totally different. This was tested for
+ * * pairs that differed by one bit, by two bits, in any combination
+ * of top bits of (a,b,c), or in any combination of bottom bits of
+ * (a,b,c).
+ * * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
+ * the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
+ * is commonly produced by subtraction) look like a single 1-bit
+ * difference.
+ * * the base values were pseudorandom, all zero but one bit set, or
+ * all zero plus a counter that starts at zero.
+ *
+ * The use of separate functions for mix() and final() allow for a
+ * substantial performance increase since final() does not need to
+ * do well in reverse, but is does need to affect all output bits.
+ * mix(), on the other hand, does not need to affect all output
+ * bits (affecting 32 bits is enough). The original hash function had
+ * a single mixing operation that had to satisfy both sets of requirements
+ * and was slower as a result.
+ *----------
+ */
+#define final(a,b,c) \
+{ \
+ c ^= b; c -= rot(b,14); \
+ a ^= c; a -= rot(c,11); \
+ b ^= a; b -= rot(a,25); \
+ c ^= b; c -= rot(b,16); \
+ a ^= c; a -= rot(c, 4); \
+ b ^= a; b -= rot(a,14); \
+ c ^= b; c -= rot(b,24); \
}
/*
@@ -260,8 +316,7 @@ hash_any(register const unsigned char *k, register int keylen)
/* Set up the internal state */
len = keylen;
- a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
- c = 3923095; /* initialize with an arbitrary value */
+ a = b = c = 0x9e3779b9 + len + 3923095;
/* If the source pointer is word-aligned, we use word-wide fetches */
if (((long) k & UINT32_ALIGN_MASK) == 0)
@@ -282,7 +337,6 @@ hash_any(register const unsigned char *k, register int keylen)
/* handle the last 11 bytes */
k = (const unsigned char *) ka;
- c += keylen;
#ifdef WORDS_BIGENDIAN
switch (len)
{
@@ -385,7 +439,6 @@ hash_any(register const unsigned char *k, register int keylen)
}
/* handle the last 11 bytes */
- c += keylen;
#ifdef WORDS_BIGENDIAN
switch (len) /* all the case statements fall through */
{
@@ -445,7 +498,7 @@ hash_any(register const unsigned char *k, register int keylen)
#endif /* WORDS_BIGENDIAN */
}
- mix(a, b, c);
+ final(a, b, c);
/* report the result */
return UInt32GetDatum(c);
@@ -465,11 +518,10 @@ hash_uint32(uint32 k)
b,
c;
- a = 0x9e3779b9 + k;
- b = 0x9e3779b9;
- c = 3923095 + (uint32) sizeof(uint32);
+ a = b = c = 0x9e3779b9 + (uint32) sizeof(uint32) + 3923095;
+ a += k;
- mix(a, b, c);
+ final(a, b, c);
/* report the result */
return UInt32GetDatum(c);
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index d02bde48c82..08b2969d96f 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -37,7 +37,7 @@
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.522 2009/02/09 20:57:59 alvherre Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.523 2009/02/09 21:18:28 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -53,6 +53,6 @@
*/
/* yyyymmddN */
-#define CATALOG_VERSION_NO 200902091
+#define CATALOG_VERSION_NO 200902092
#endif
diff --git a/src/test/regress/expected/polymorphism.out b/src/test/regress/expected/polymorphism.out
index aace99cb625..7648ad610bc 100644
--- a/src/test/regress/expected/polymorphism.out
+++ b/src/test/regress/expected/polymorphism.out
@@ -352,188 +352,188 @@ insert into t values(2,array[222],'c');
insert into t values(3,array[3],'a');
insert into t values(3,array[3],'b');
-- test the successfully created polymorphic aggregates
-select f3, myaggp01a(*) from t group by f3;
+select f3, myaggp01a(*) from t group by f3 order by f3;
f3 | myaggp01a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggp03a(*) from t group by f3;
+select f3, myaggp03a(*) from t group by f3 order by f3;
f3 | myaggp03a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggp03b(*) from t group by f3;
+select f3, myaggp03b(*) from t group by f3 order by f3;
f3 | myaggp03b
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggp05a(f1) from t group by f3;
+select f3, myaggp05a(f1) from t group by f3 order by f3;
f3 | myaggp05a
----+-----------
+ a | {1,2,3}
b | {1,2,3}
c | {1,2}
- a | {1,2,3}
(3 rows)
-select f3, myaggp06a(f1) from t group by f3;
+select f3, myaggp06a(f1) from t group by f3 order by f3;
f3 | myaggp06a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggp08a(f1) from t group by f3;
+select f3, myaggp08a(f1) from t group by f3 order by f3;
f3 | myaggp08a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggp09a(f1) from t group by f3;
+select f3, myaggp09a(f1) from t group by f3 order by f3;
f3 | myaggp09a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggp09b(f1) from t group by f3;
+select f3, myaggp09b(f1) from t group by f3 order by f3;
f3 | myaggp09b
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggp10a(f1) from t group by f3;
+select f3, myaggp10a(f1) from t group by f3 order by f3;
f3 | myaggp10a
----+-----------
+ a | {1,2,3}
b | {1,2,3}
c | {1,2}
- a | {1,2,3}
(3 rows)
-select f3, myaggp10b(f1) from t group by f3;
+select f3, myaggp10b(f1) from t group by f3 order by f3;
f3 | myaggp10b
----+-----------
+ a | {1,2,3}
b | {1,2,3}
c | {1,2}
- a | {1,2,3}
(3 rows)
-select f3, myaggp20a(f1) from t group by f3;
+select f3, myaggp20a(f1) from t group by f3 order by f3;
f3 | myaggp20a
----+-----------
+ a | {1,2,3}
b | {1,2,3}
c | {1,2}
- a | {1,2,3}
(3 rows)
-select f3, myaggp20b(f1) from t group by f3;
+select f3, myaggp20b(f1) from t group by f3 order by f3;
f3 | myaggp20b
----+-----------
+ a | {1,2,3}
b | {1,2,3}
c | {1,2}
- a | {1,2,3}
(3 rows)
-select f3, myaggn01a(*) from t group by f3;
+select f3, myaggn01a(*) from t group by f3 order by f3;
f3 | myaggn01a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggn01b(*) from t group by f3;
+select f3, myaggn01b(*) from t group by f3 order by f3;
f3 | myaggn01b
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggn03a(*) from t group by f3;
+select f3, myaggn03a(*) from t group by f3 order by f3;
f3 | myaggn03a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggn05a(f1) from t group by f3;
+select f3, myaggn05a(f1) from t group by f3 order by f3;
f3 | myaggn05a
----+-----------
+ a | {1,2,3}
b | {1,2,3}
c | {1,2}
- a | {1,2,3}
(3 rows)
-select f3, myaggn05b(f1) from t group by f3;
+select f3, myaggn05b(f1) from t group by f3 order by f3;
f3 | myaggn05b
----+-----------
+ a | {1,2,3}
b | {1,2,3}
c | {1,2}
- a | {1,2,3}
(3 rows)
-select f3, myaggn06a(f1) from t group by f3;
+select f3, myaggn06a(f1) from t group by f3 order by f3;
f3 | myaggn06a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggn06b(f1) from t group by f3;
+select f3, myaggn06b(f1) from t group by f3 order by f3;
f3 | myaggn06b
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggn08a(f1) from t group by f3;
+select f3, myaggn08a(f1) from t group by f3 order by f3;
f3 | myaggn08a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggn08b(f1) from t group by f3;
+select f3, myaggn08b(f1) from t group by f3 order by f3;
f3 | myaggn08b
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggn09a(f1) from t group by f3;
+select f3, myaggn09a(f1) from t group by f3 order by f3;
f3 | myaggn09a
----+-----------
+ a | {}
b | {}
c | {}
- a | {}
(3 rows)
-select f3, myaggn10a(f1) from t group by f3;
+select f3, myaggn10a(f1) from t group by f3 order by f3;
f3 | myaggn10a
----+-----------
+ a | {1,2,3}
b | {1,2,3}
c | {1,2}
- a | {1,2,3}
(3 rows)
select mysum2(f1, f1 + 1) from t;
diff --git a/src/test/regress/expected/union.out b/src/test/regress/expected/union.out
index 295dacea86d..be046a9b632 100644
--- a/src/test/regress/expected/union.out
+++ b/src/test/regress/expected/union.out
@@ -263,16 +263,16 @@ ORDER BY 1;
SELECT q2 FROM int8_tbl INTERSECT SELECT q1 FROM int8_tbl;
q2
------------------
- 123
4567890123456789
+ 123
(2 rows)
SELECT q2 FROM int8_tbl INTERSECT ALL SELECT q1 FROM int8_tbl;
q2
------------------
- 123
4567890123456789
4567890123456789
+ 123
(3 rows)
SELECT q2 FROM int8_tbl EXCEPT SELECT q1 FROM int8_tbl ORDER BY 1;
@@ -305,16 +305,16 @@ SELECT q1 FROM int8_tbl EXCEPT SELECT q2 FROM int8_tbl;
SELECT q1 FROM int8_tbl EXCEPT ALL SELECT q2 FROM int8_tbl;
q1
------------------
- 123
4567890123456789
+ 123
(2 rows)
SELECT q1 FROM int8_tbl EXCEPT ALL SELECT DISTINCT q2 FROM int8_tbl;
q1
------------------
- 123
4567890123456789
4567890123456789
+ 123
(3 rows)
--
@@ -341,8 +341,8 @@ SELECT f1 FROM float8_tbl EXCEPT SELECT f1 FROM int4_tbl ORDER BY 1;
SELECT q1 FROM int8_tbl INTERSECT SELECT q2 FROM int8_tbl UNION ALL SELECT q2 FROM int8_tbl;
q1
-------------------
- 123
4567890123456789
+ 123
456
4567890123456789
123
@@ -353,15 +353,15 @@ SELECT q1 FROM int8_tbl INTERSECT SELECT q2 FROM int8_tbl UNION ALL SELECT q2 FR
SELECT q1 FROM int8_tbl INTERSECT (((SELECT q2 FROM int8_tbl UNION ALL SELECT q2 FROM int8_tbl)));
q1
------------------
- 123
4567890123456789
+ 123
(2 rows)
(((SELECT q1 FROM int8_tbl INTERSECT SELECT q2 FROM int8_tbl))) UNION ALL SELECT q2 FROM int8_tbl;
q1
-------------------
- 123
4567890123456789
+ 123
456
4567890123456789
123
@@ -416,8 +416,8 @@ LINE 1: ... int8_tbl EXCEPT SELECT q2 FROM int8_tbl ORDER BY q2 LIMIT 1...
SELECT q1 FROM int8_tbl EXCEPT (((SELECT q2 FROM int8_tbl ORDER BY q2 LIMIT 1)));
q1
------------------
- 123
4567890123456789
+ 123
(2 rows)
--
diff --git a/src/test/regress/sql/polymorphism.sql b/src/test/regress/sql/polymorphism.sql
index bbac7d11a55..c01871de007 100644
--- a/src/test/regress/sql/polymorphism.sql
+++ b/src/test/regress/sql/polymorphism.sql
@@ -350,29 +350,29 @@ insert into t values(3,array[3],'a');
insert into t values(3,array[3],'b');
-- test the successfully created polymorphic aggregates
-select f3, myaggp01a(*) from t group by f3;
-select f3, myaggp03a(*) from t group by f3;
-select f3, myaggp03b(*) from t group by f3;
-select f3, myaggp05a(f1) from t group by f3;
-select f3, myaggp06a(f1) from t group by f3;
-select f3, myaggp08a(f1) from t group by f3;
-select f3, myaggp09a(f1) from t group by f3;
-select f3, myaggp09b(f1) from t group by f3;
-select f3, myaggp10a(f1) from t group by f3;
-select f3, myaggp10b(f1) from t group by f3;
-select f3, myaggp20a(f1) from t group by f3;
-select f3, myaggp20b(f1) from t group by f3;
-select f3, myaggn01a(*) from t group by f3;
-select f3, myaggn01b(*) from t group by f3;
-select f3, myaggn03a(*) from t group by f3;
-select f3, myaggn05a(f1) from t group by f3;
-select f3, myaggn05b(f1) from t group by f3;
-select f3, myaggn06a(f1) from t group by f3;
-select f3, myaggn06b(f1) from t group by f3;
-select f3, myaggn08a(f1) from t group by f3;
-select f3, myaggn08b(f1) from t group by f3;
-select f3, myaggn09a(f1) from t group by f3;
-select f3, myaggn10a(f1) from t group by f3;
+select f3, myaggp01a(*) from t group by f3 order by f3;
+select f3, myaggp03a(*) from t group by f3 order by f3;
+select f3, myaggp03b(*) from t group by f3 order by f3;
+select f3, myaggp05a(f1) from t group by f3 order by f3;
+select f3, myaggp06a(f1) from t group by f3 order by f3;
+select f3, myaggp08a(f1) from t group by f3 order by f3;
+select f3, myaggp09a(f1) from t group by f3 order by f3;
+select f3, myaggp09b(f1) from t group by f3 order by f3;
+select f3, myaggp10a(f1) from t group by f3 order by f3;
+select f3, myaggp10b(f1) from t group by f3 order by f3;
+select f3, myaggp20a(f1) from t group by f3 order by f3;
+select f3, myaggp20b(f1) from t group by f3 order by f3;
+select f3, myaggn01a(*) from t group by f3 order by f3;
+select f3, myaggn01b(*) from t group by f3 order by f3;
+select f3, myaggn03a(*) from t group by f3 order by f3;
+select f3, myaggn05a(f1) from t group by f3 order by f3;
+select f3, myaggn05b(f1) from t group by f3 order by f3;
+select f3, myaggn06a(f1) from t group by f3 order by f3;
+select f3, myaggn06b(f1) from t group by f3 order by f3;
+select f3, myaggn08a(f1) from t group by f3 order by f3;
+select f3, myaggn08b(f1) from t group by f3 order by f3;
+select f3, myaggn09a(f1) from t group by f3 order by f3;
+select f3, myaggn10a(f1) from t group by f3 order by f3;
select mysum2(f1, f1 + 1) from t;
-- test inlining of polymorphic SQL functions
--
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