On Sun, 2007-06-05 at 21:30 -0400, Tom Lane wrote:
> You can do it always if you simply decrement the weight for each leading
> zero removed.
On reflection, the patch as given was wrong anyway: if two Numerics are
identical except for the presence of leading zeroes, we can't consider
the weight when hashing one of them but not the other.
> The patch as given is wrong since it makes the test for no-digits
> before instead of after removing zeroes.)
Okay, how about the attached revision?
> It'd be a good idea if you repeat the previous number-of-collisions
> experiment on this code.
I'll do this shortly.
-Neil
Index: src/backend/utils/adt/numeric.c
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/backend/utils/adt/numeric.c,v
retrieving revision 1.101
diff -c -p -r1.101 numeric.c
*** src/backend/utils/adt/numeric.c 27 Feb 2007 23:48:08 -0000 1.101
--- src/backend/utils/adt/numeric.c 7 May 2007 01:49:18 -0000
***************
*** 26,31 ****
--- 26,32 ----
#include <limits.h>
#include <math.h>
+ #include "access/hash.h"
#include "catalog/pg_type.h"
#include "libpq/pqformat.h"
#include "utils/array.h"
*************** cmp_numerics(Numeric num1, Numeric num2)
*** 1149,1154 ****
--- 1150,1230 ----
return result;
}
+ Datum
+ hash_numeric(PG_FUNCTION_ARGS)
+ {
+ Numeric key = PG_GETARG_NUMERIC(0);
+ Datum digit_hash;
+ Datum result;
+ int weight;
+ int start_offset;
+ int end_offset;
+ int i;
+ int hash_len;
+
+ /* If it's NaN, don't try to hash the rest of the fields */
+ if (NUMERIC_IS_NAN(key))
+ PG_RETURN_UINT32(0);
+
+ weight = key->n_weight;
+ start_offset = 0;
+ end_offset = 0;
+
+ /*
+ * Omit any leading or trailing zeros from the input to the
+ * hash. The numeric implementation *should* guarantee that
+ * leading and trailing zeros are suppressed, but we're
+ * paranoid. Note that we measure the starting and ending offsets
+ * in units of NumericDigits, not bytes.
+ */
+ for (i = 0; i < NUMERIC_NDIGITS(key); i++)
+ {
+ if (NUMERIC_DIGITS(key)[i] != (NumericDigit) 0)
+ break;
+
+ start_offset++;
+ /*
+ * The weight is effectively the # of digits before the
+ * decimal point, so decrement it for each leading zero we
+ * skip.
+ */
+ weight--;
+ }
+
+ /*
+ * If there are no non-zero digits, then the value of the number
+ * is zero, regardless of any other fields.
+ */
+ if (NUMERIC_NDIGITS(key) == start_offset)
+ PG_RETURN_UINT32(-1);
+
+ for (i = NUMERIC_NDIGITS(key) - 1; i >= 0; i--)
+ {
+ if (NUMERIC_DIGITS(key)[i] != (NumericDigit) 0)
+ break;
+
+ end_offset++;
+ }
+
+ /* If we get here, there should be at least one non-zero digit */
+ Assert(start_offset + end_offset < NUMERIC_NDIGITS(key));
+
+ /*
+ * Note that we don't hash on the Numeric's scale, since two
+ * numerics can compare equal but have different scales. We also
+ * don't hash on the sign, although we could: since a sign
+ * difference implies inequality, this shouldn't affect correctness.
+ */
+ hash_len = NUMERIC_NDIGITS(key) - start_offset - end_offset;
+ digit_hash = hash_any((unsigned char *) (NUMERIC_DIGITS(key) + start_offset),
+ hash_len * sizeof(NumericDigit));
+
+ /* Mix in the weight, via XOR */
+ result = digit_hash ^ weight;
+
+ PG_RETURN_DATUM(result);
+ }
+
/* ----------------------------------------------------------------------
*
Index: src/include/catalog/pg_amop.h
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/include/catalog/pg_amop.h,v
retrieving revision 1.80
diff -c -p -r1.80 pg_amop.h
*** src/include/catalog/pg_amop.h 2 Apr 2007 03:49:40 -0000 1.80
--- src/include/catalog/pg_amop.h 7 May 2007 00:48:32 -0000
*************** DATA(insert ( 2232 19 19 1 f 2334 405
*** 568,573 ****
--- 568,575 ----
DATA(insert ( 2235 1033 1033 1 f 974 405 ));
/* uuid_ops */
DATA(insert ( 2969 2950 2950 1 f 2972 405 ));
+ /* numeric_ops */
+ DATA(insert ( 1998 1700 1700 1 f 1752 405 ));
/*
Index: src/include/catalog/pg_amproc.h
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/include/catalog/pg_amproc.h,v
retrieving revision 1.64
diff -c -p -r1.64 pg_amproc.h
*** src/include/catalog/pg_amproc.h 2 Apr 2007 03:49:40 -0000 1.64
--- src/include/catalog/pg_amproc.h 7 May 2007 00:48:32 -0000
*************** DATA(insert ( 1990 26 26 1 453 ));
*** 148,153 ****
--- 148,154 ----
DATA(insert ( 1992 30 30 1 457 ));
DATA(insert ( 1995 25 25 1 400 ));
DATA(insert ( 1997 1083 1083 1 452 ));
+ DATA(insert ( 1998 1700 1700 1 432 ));
DATA(insert ( 1999 1184 1184 1 452 ));
DATA(insert ( 2001 1266 1266 1 1696 ));
DATA(insert ( 2040 1114 1114 1 452 ));
Index: src/include/catalog/pg_opclass.h
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/include/catalog/pg_opclass.h,v
retrieving revision 1.75
diff -c -p -r1.75 pg_opclass.h
*** src/include/catalog/pg_opclass.h 2 Apr 2007 03:49:40 -0000 1.75
--- src/include/catalog/pg_opclass.h 7 May 2007 00:48:32 -0000
*************** DATA(insert ( 405 macaddr_ops PGNSP P
*** 129,134 ****
--- 129,135 ----
DATA(insert ( 403 name_ops PGNSP PGUID 1986 19 t 0 ));
DATA(insert ( 405 name_ops PGNSP PGUID 1987 19 t 0 ));
DATA(insert ( 403 numeric_ops PGNSP PGUID 1988 1700 t 0 ));
+ DATA(insert ( 405 numeric_ops PGNSP PGUID 1998 1700 t 0 ));
DATA(insert OID = 1981 ( 403 oid_ops PGNSP PGUID 1989 26 t 0 ));
#define OID_BTREE_OPS_OID 1981
DATA(insert ( 405 oid_ops PGNSP PGUID 1990 26 t 0 ));
Index: src/include/catalog/pg_operator.h
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/include/catalog/pg_operator.h,v
retrieving revision 1.151
diff -c -p -r1.151 pg_operator.h
*** src/include/catalog/pg_operator.h 2 Apr 2007 03:49:40 -0000 1.151
--- src/include/catalog/pg_operator.h 7 May 2007 00:48:32 -0000
*************** DATA(insert OID = 1630 ( "!~~*" PGNSP
*** 675,681 ****
/* NUMERIC type - OID's 1700-1799 */
DATA(insert OID = 1751 ( "-" PGNSP PGUID l f f 0 1700 1700 0 0 numeric_uminus - - ));
! DATA(insert OID = 1752 ( "=" PGNSP PGUID b t f 1700 1700 16 1752 1753 numeric_eq eqsel eqjoinsel ));
DATA(insert OID = 1753 ( "<>" PGNSP PGUID b f f 1700 1700 16 1753 1752 numeric_ne neqsel neqjoinsel ));
DATA(insert OID = 1754 ( "<" PGNSP PGUID b f f 1700 1700 16 1756 1757 numeric_lt scalarltsel scalarltjoinsel ));
DATA(insert OID = 1755 ( "<=" PGNSP PGUID b f f 1700 1700 16 1757 1756 numeric_le scalarltsel scalarltjoinsel ));
--- 675,681 ----
/* NUMERIC type - OID's 1700-1799 */
DATA(insert OID = 1751 ( "-" PGNSP PGUID l f f 0 1700 1700 0 0 numeric_uminus - - ));
! DATA(insert OID = 1752 ( "=" PGNSP PGUID b t t 1700 1700 16 1752 1753 numeric_eq eqsel eqjoinsel ));
DATA(insert OID = 1753 ( "<>" PGNSP PGUID b f f 1700 1700 16 1753 1752 numeric_ne neqsel neqjoinsel ));
DATA(insert OID = 1754 ( "<" PGNSP PGUID b f f 1700 1700 16 1756 1757 numeric_lt scalarltsel scalarltjoinsel ));
DATA(insert OID = 1755 ( "<=" PGNSP PGUID b f f 1700 1700 16 1757 1756 numeric_le scalarltsel scalarltjoinsel ));
Index: src/include/catalog/pg_opfamily.h
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/include/catalog/pg_opfamily.h,v
retrieving revision 1.4
diff -c -p -r1.4 pg_opfamily.h
*** src/include/catalog/pg_opfamily.h 2 Apr 2007 03:49:40 -0000 1.4
--- src/include/catalog/pg_opfamily.h 7 May 2007 00:48:32 -0000
*************** DATA(insert OID = 1986 ( 403 name_ops
*** 93,98 ****
--- 93,99 ----
#define NAME_BTREE_FAM_OID 1986
DATA(insert OID = 1987 ( 405 name_ops PGNSP PGUID ));
DATA(insert OID = 1988 ( 403 numeric_ops PGNSP PGUID ));
+ DATA(insert OID = 1998 ( 405 numeric_ops PGNSP PGUID ));
DATA(insert OID = 1989 ( 403 oid_ops PGNSP PGUID ));
#define OID_BTREE_FAM_OID 1989
DATA(insert OID = 1990 ( 405 oid_ops PGNSP PGUID ));
Index: src/include/catalog/pg_proc.h
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/include/catalog/pg_proc.h,v
retrieving revision 1.454
diff -c -p -r1.454 pg_proc.h
*** src/include/catalog/pg_proc.h 2 Apr 2007 03:49:40 -0000 1.454
--- src/include/catalog/pg_proc.h 7 May 2007 01:07:21 -0000
*************** DATA(insert OID = 399 ( hashmacaddr
*** 838,843 ****
--- 838,845 ----
DESCR("hash");
DATA(insert OID = 422 ( hashinet PGNSP PGUID 12 1 0 f f t f i 1 23 "869" _null_ _null_ _null_ hashinet - _null_ ));
DESCR("hash");
+ DATA(insert OID = 432 ( hash_numeric PGNSP PGUID 12 1 0 f f t f i 1 23 "1700" _null_ _null_ _null_ hash_numeric - _null_ ));
+ DESCR("hash");
DATA(insert OID = 458 ( text_larger PGNSP PGUID 12 1 0 f f t f i 2 25 "25 25" _null_ _null_ _null_ text_larger - _null_ ));
DESCR("larger of two");
DATA(insert OID = 459 ( text_smaller PGNSP PGUID 12 1 0 f f t f i 2 25 "25 25" _null_ _null_ _null_ text_smaller - _null_ ));
Index: src/include/utils/builtins.h
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/include/utils/builtins.h,v
retrieving revision 1.291
diff -c -p -r1.291 builtins.h
*** src/include/utils/builtins.h 2 Apr 2007 03:49:41 -0000 1.291
--- src/include/utils/builtins.h 7 May 2007 01:07:12 -0000
*************** extern Datum int2_avg_accum(PG_FUNCTION_
*** 883,888 ****
--- 883,889 ----
extern Datum int4_avg_accum(PG_FUNCTION_ARGS);
extern Datum int8_avg(PG_FUNCTION_ARGS);
extern Datum width_bucket_numeric(PG_FUNCTION_ARGS);
+ extern Datum hash_numeric(PG_FUNCTION_ARGS);
/* ri_triggers.c */
extern Datum RI_FKey_check_ins(PG_FUNCTION_ARGS);
---------------------------(end of broadcast)---------------------------
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