*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/hash/hashfunc.c,v 1.55 2008/01/01 19:45:46 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/hash/hashfunc.c,v 1.56 2008/04/06 16:54:48 tgl Exp $
*
* NOTES
* These functions are stored in pg_amproc. For each operator class
* for PostgreSQL by Neil Conway. For more information on this
* 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.
*/
+/* Get a bit mask of the bits set in non-uint32 aligned addresses */
+#define UINT32_ALIGN_MASK (sizeof(uint32) - 1)
+
/*----------
* mix -- mix 3 32-bit values reversibly.
* For every delta with one or two bits set, and the deltas of all three
* About 6*len+35 instructions. The best hash table sizes are powers
* of 2. There is no need to do mod a prime (mod is sooo slow!).
* If you need less than 32 bits, use a bitmask.
+ *
+ * Note: we could easily change this function to return a 64-bit hash value
+ * by using the final values of both b and c. b is perhaps a little less
+ * well mixed than c, however.
*/
Datum
hash_any(register const unsigned char *k, register int keylen)
a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
c = 3923095; /* initialize with an arbitrary value */
- /* handle most of the key */
- while (len >= 12)
+ /* If the source pointer is word-aligned, we use word-wide fetches */
+ if (((long) k & UINT32_ALIGN_MASK) == 0)
{
- a += (k[0] + ((uint32) k[1] << 8) + ((uint32) k[2] << 16) + ((uint32) k[3] << 24));
- b += (k[4] + ((uint32) k[5] << 8) + ((uint32) k[6] << 16) + ((uint32) k[7] << 24));
- c += (k[8] + ((uint32) k[9] << 8) + ((uint32) k[10] << 16) + ((uint32) k[11] << 24));
- mix(a, b, c);
- k += 12;
- len -= 12;
+ /* Code path for aligned source data */
+ register const uint32 *ka = (const uint32 *) k;
+
+ /* handle most of the key */
+ while (len >= 12)
+ {
+ a += ka[0];
+ b += ka[1];
+ c += ka[2];
+ mix(a, b, c);
+ ka += 3;
+ len -= 12;
+ }
+
+ /* handle the last 11 bytes */
+ k = (const unsigned char *) ka;
+ c += keylen;
+#ifdef WORDS_BIGENDIAN
+ switch (len)
+ {
+ case 11:
+ c += ((uint32) k[10] << 8);
+ /* fall through */
+ case 10:
+ c += ((uint32) k[9] << 16);
+ /* fall through */
+ case 9:
+ c += ((uint32) k[8] << 24);
+ /* the lowest byte of c is reserved for the length */
+ /* fall through */
+ case 8:
+ b += ka[1];
+ a += ka[0];
+ break;
+ case 7:
+ b += ((uint32) k[6] << 8);
+ /* fall through */
+ case 6:
+ b += ((uint32) k[5] << 16);
+ /* fall through */
+ case 5:
+ b += ((uint32) k[4] << 24);
+ /* fall through */
+ case 4:
+ a += ka[0];
+ break;
+ case 3:
+ a += ((uint32) k[2] << 8);
+ /* fall through */
+ case 2:
+ a += ((uint32) k[1] << 16);
+ /* fall through */
+ case 1:
+ a += ((uint32) k[0] << 24);
+ /* case 0: nothing left to add */
+ }
+#else /* !WORDS_BIGENDIAN */
+ switch (len)
+ {
+ case 11:
+ c += ((uint32) k[10] << 24);
+ /* fall through */
+ case 10:
+ c += ((uint32) k[9] << 16);
+ /* fall through */
+ case 9:
+ c += ((uint32) k[8] << 8);
+ /* the lowest byte of c is reserved for the length */
+ /* fall through */
+ case 8:
+ b += ka[1];
+ a += ka[0];
+ break;
+ case 7:
+ b += ((uint32) k[6] << 16);
+ /* fall through */
+ case 6:
+ b += ((uint32) k[5] << 8);
+ /* fall through */
+ case 5:
+ b += k[4];
+ /* fall through */
+ case 4:
+ a += ka[0];
+ break;
+ case 3:
+ a += ((uint32) k[2] << 16);
+ /* fall through */
+ case 2:
+ a += ((uint32) k[1] << 8);
+ /* fall through */
+ case 1:
+ a += k[0];
+ /* case 0: nothing left to add */
+ }
+#endif /* WORDS_BIGENDIAN */
}
-
- /* handle the last 11 bytes */
- c += keylen;
- switch (len) /* all the case statements fall through */
+ else
{
- case 11:
- c += ((uint32) k[10] << 24);
- case 10:
- c += ((uint32) k[9] << 16);
- case 9:
- c += ((uint32) k[8] << 8);
- /* the first byte of c is reserved for the length */
- case 8:
- b += ((uint32) k[7] << 24);
- case 7:
- b += ((uint32) k[6] << 16);
- case 6:
- b += ((uint32) k[5] << 8);
- case 5:
- b += k[4];
- case 4:
- a += ((uint32) k[3] << 24);
- case 3:
- a += ((uint32) k[2] << 16);
- case 2:
- a += ((uint32) k[1] << 8);
- case 1:
- a += k[0];
+ /* Code path for non-aligned source data */
+
+ /* handle most of the key */
+ while (len >= 12)
+ {
+#ifdef WORDS_BIGENDIAN
+ a += (k[3] + ((uint32) k[2] << 8) + ((uint32) k[1] << 16) + ((uint32) k[0] << 24));
+ b += (k[7] + ((uint32) k[6] << 8) + ((uint32) k[5] << 16) + ((uint32) k[4] << 24));
+ c += (k[11] + ((uint32) k[10] << 8) + ((uint32) k[9] << 16) + ((uint32) k[8] << 24));
+#else /* !WORDS_BIGENDIAN */
+ a += (k[0] + ((uint32) k[1] << 8) + ((uint32) k[2] << 16) + ((uint32) k[3] << 24));
+ b += (k[4] + ((uint32) k[5] << 8) + ((uint32) k[6] << 16) + ((uint32) k[7] << 24));
+ c += (k[8] + ((uint32) k[9] << 8) + ((uint32) k[10] << 16) + ((uint32) k[11] << 24));
+#endif /* WORDS_BIGENDIAN */
+ mix(a, b, c);
+ k += 12;
+ len -= 12;
+ }
+
+ /* handle the last 11 bytes */
+ c += keylen;
+#ifdef WORDS_BIGENDIAN
+ switch (len) /* all the case statements fall through */
+ {
+ case 11:
+ c += ((uint32) k[10] << 8);
+ case 10:
+ c += ((uint32) k[9] << 16);
+ case 9:
+ c += ((uint32) k[8] << 24);
+ /* the lowest byte of c is reserved for the length */
+ case 8:
+ b += k[7];
+ case 7:
+ b += ((uint32) k[6] << 8);
+ case 6:
+ b += ((uint32) k[5] << 16);
+ case 5:
+ b += ((uint32) k[4] << 24);
+ case 4:
+ a += k[3];
+ case 3:
+ a += ((uint32) k[2] << 8);
+ case 2:
+ a += ((uint32) k[1] << 16);
+ case 1:
+ a += ((uint32) k[0] << 24);
/* case 0: nothing left to add */
+ }
+#else /* !WORDS_BIGENDIAN */
+ switch (len) /* all the case statements fall through */
+ {
+ case 11:
+ c += ((uint32) k[10] << 24);
+ case 10:
+ c += ((uint32) k[9] << 16);
+ case 9:
+ c += ((uint32) k[8] << 8);
+ /* the lowest byte of c is reserved for the length */
+ case 8:
+ b += ((uint32) k[7] << 24);
+ case 7:
+ b += ((uint32) k[6] << 16);
+ case 6:
+ b += ((uint32) k[5] << 8);
+ case 5:
+ b += k[4];
+ case 4:
+ a += ((uint32) k[3] << 24);
+ case 3:
+ a += ((uint32) k[2] << 16);
+ case 2:
+ a += ((uint32) k[1] << 8);
+ case 1:
+ a += k[0];
+ /* case 0: nothing left to add */
+ }
+#endif /* WORDS_BIGENDIAN */
}
+
mix(a, b, c);
/* report the result */
/*
* hash_uint32() -- hash a 32-bit value
*
- * This has the same result (at least on little-endian machines) as
+ * This has the same result as
* hash_any(&k, sizeof(uint32))
* but is faster and doesn't force the caller to store k into memory.
*/
-- leave some cursors open, to test that auto-close works.
-- record this in the system view as well (don't query the time field there
-- however)
-SELECT name, statement, is_holdable, is_binary, is_scrollable FROM pg_cursors;
+SELECT name, statement, is_holdable, is_binary, is_scrollable FROM pg_cursors ORDER BY 1;
name | statement | is_holdable | is_binary | is_scrollable
-------+-----------------------------------------------------------------------+-------------+-----------+---------------
foo13 | DECLARE foo13 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
+ foo14 | DECLARE foo14 SCROLL CURSOR FOR SELECT * FROM tenk2; | f | f | t
foo15 | DECLARE foo15 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
- foo19 | DECLARE foo19 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
+ foo16 | DECLARE foo16 SCROLL CURSOR FOR SELECT * FROM tenk2; | f | f | t
foo17 | DECLARE foo17 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
- foo14 | DECLARE foo14 SCROLL CURSOR FOR SELECT * FROM tenk2; | f | f | t
- foo21 | DECLARE foo21 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
- foo23 | DECLARE foo23 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
foo18 | DECLARE foo18 SCROLL CURSOR FOR SELECT * FROM tenk2; | f | f | t
+ foo19 | DECLARE foo19 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
foo20 | DECLARE foo20 SCROLL CURSOR FOR SELECT * FROM tenk2; | f | f | t
+ foo21 | DECLARE foo21 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
foo22 | DECLARE foo22 SCROLL CURSOR FOR SELECT * FROM tenk2; | f | f | t
- foo16 | DECLARE foo16 SCROLL CURSOR FOR SELECT * FROM tenk2; | f | f | t
+ foo23 | DECLARE foo23 SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2; | f | f | t
(11 rows)
END;
(1 row)
DECLARE bc BINARY CURSOR FOR SELECT * FROM tenk1;
-SELECT name, statement, is_holdable, is_binary, is_scrollable FROM pg_cursors;
+SELECT name, statement, is_holdable, is_binary, is_scrollable FROM pg_cursors ORDER BY 1;
name | statement | is_holdable | is_binary | is_scrollable
------+----------------------------------------------------------------------+-------------+-----------+---------------
- c2 | declare c2 cursor with hold for select count_tt1_v(), count_tt1_s(); | t | f | f
bc | DECLARE bc BINARY CURSOR FOR SELECT * FROM tenk1; | f | t | t
+ c2 | declare c2 cursor with hold for select count_tt1_v(), count_tt1_s(); | t | f | f
(2 rows)
ROLLBACK;
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