Commit f468b91f authored by unknown's avatar unknown
Browse files

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

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.
parent 350ad500

myisam/mi_unique.c

+3 −3
Original line number Diff line number Diff line
@@ -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)