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Fix for Bug#3904 "COUNT DISTINCT performance anomaly in 4.1"

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The bug was caused by error in hash calculation function: it
always returned hash value for last field in a composite key, so 
for keys like (a text, b char(1)) we were always
getting bad hash values.
 


myisam/mi_unique.c:
  Fix for bug #3904:
  We should take into account existing hash value when calculating hash for
  next key in a composite unique index.
This commit is contained in:
unknown 2004-06-10 01:30:39 +04:00
commit f468b91f37
1 changed files with 3 additions and 3 deletions
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6
myisam/mi_unique.c
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@ -71,6 +71,7 @@ ha_checksum mi_unique_hash(MI_UNIQUEDEF *def, const byte *record)
const byte *pos, *end;
ha_checksum crc=0;
HA_KEYSEG *keyseg;
ulong seed= 4;
for (keyseg=def->seg ; keyseg < def->end ; keyseg++)
{
@ -108,9 +109,8 @@ ha_checksum mi_unique_hash(MI_UNIQUEDEF *def, const byte *record)
end= pos+length;
if (type == HA_KEYTYPE_TEXT || type == HA_KEYTYPE_VARTEXT)
{
ulong nr=1, nr2=4;
keyseg->charset->coll->hash_sort(keyseg->charset,(const uchar*)pos,length,&nr, &nr2);
crc=nr;
keyseg->charset->coll->hash_sort(keyseg->charset,
(const uchar*) pos, length, &crc, &seed);
}
else
while (pos != end)