mi_unique.c

/* Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/* Functions to check if a row is unique */

#include "myisamdef.h"
#include <m_ctype.h>

my_bool mi_check_unique(MI_INFO *info, MI_UNIQUEDEF *def, uchar *record,
                        ha_checksum unique_hash, my_off_t disk_pos)
{
  my_off_t lastpos=info->lastpos;
  MI_KEYDEF *key= &info->s->keyinfo[def->key];
  uchar *key_buff=info->lastkey2;
  DBUG_ENTER("mi_check_unique");

  mi_unique_store(record+key->seg->start, unique_hash);
  _mi_make_key(info,def->key,key_buff,record,0);

  /* The above changed info->lastkey2. Inform mi_rnext_same(). */
  info->update&= ~HA_STATE_RNEXT_SAME;

  if (_mi_search(info,info->s->keyinfo+def->key,key_buff,MI_UNIQUE_HASH_LENGTH,
                 SEARCH_FIND,info->s->state.key_root[def->key]))
  {
    info->page_changed=1;                       /* Can't optimize read next */
    info->lastpos= lastpos;
    DBUG_RETURN(0);                             /* No matching rows */
  }

  for (;;)
  {
    if (info->lastpos != disk_pos &&
        !(*info->s->compare_unique)(info,def,record,info->lastpos))
    {
      my_errno=HA_ERR_FOUND_DUPP_UNIQUE;
      info->errkey= (int) def->key;
      info->dupp_key_pos= info->lastpos;
      info->page_changed=1;                     /* Can't optimize read next */
      info->lastpos=lastpos;
      DBUG_PRINT("info",("Found duplicate"));
      DBUG_RETURN(1);                           /* Found identical  */
    }
    if (_mi_search_next(info,info->s->keyinfo+def->key, info->lastkey,
                        MI_UNIQUE_HASH_LENGTH, SEARCH_BIGGER,
                        info->s->state.key_root[def->key]) ||
        memcmp(info->lastkey, key_buff, MI_UNIQUE_HASH_LENGTH))
    {
      info->page_changed=1;                     /* Can't optimize read next */
      info->lastpos=lastpos;
      DBUG_RETURN(0);                           /* end of tree */
    }
  }
}


/*
  Calculate a hash for a row

  TODO
    Add support for bit fields
*/

ha_checksum mi_unique_hash(MI_UNIQUEDEF *def, const uchar *record)
{
  const uchar *pos, *end;
  ha_checksum crc= 0;
  ulong seed1=0, seed2= 4;
  HA_KEYSEG *keyseg;

  for (keyseg=def->seg ; keyseg < def->end ; keyseg++)
  {
    enum ha_base_keytype type=(enum ha_base_keytype) keyseg->type;
    uint length=keyseg->length;

    if (keyseg->null_bit)
    {
      if (record[keyseg->null_pos] & keyseg->null_bit)
      {
        /*
          Change crc in a way different from an empty string or 0.
          (This is an optimisation;  The code will work even if this isn't
          done)
        */
        crc=((crc << 8) + 511+
             (crc >> (8*sizeof(ha_checksum)-8)));
        continue;
      }
    }
    pos= record+keyseg->start;
    if (keyseg->flag & HA_VAR_LENGTH_PART)
    {
      uint pack_length=  keyseg->bit_start;
      uint tmp_length= (pack_length == 1 ? (uint) *(uchar*) pos :
                        uint2korr(pos));
      pos+= pack_length;                        /* Skip VARCHAR length */
      set_if_smaller(length,tmp_length);
    }
    else if (keyseg->flag & HA_BLOB_PART)
    {
      uint tmp_length=_mi_calc_blob_length(keyseg->bit_start,pos);
      memcpy(&pos, pos+keyseg->bit_start, sizeof(char*));
      if (!length || length > tmp_length)
        length=tmp_length;                      /* The whole blob */
    }
    end= pos+length;
    if (type == HA_KEYTYPE_TEXT || type == HA_KEYTYPE_VARTEXT1 ||
        type == HA_KEYTYPE_VARTEXT2)
    {
      keyseg->charset->coll->hash_sort(keyseg->charset,
                                       (const uchar*) pos, length, &seed1,
                                       &seed2);
      crc^= seed1;
    }
    else
      while (pos != end)
        crc=((crc << 8) +
             (((uchar)  *(uchar*) pos++))) +
          (crc >> (8*sizeof(ha_checksum)-8));
  }
  return crc;
}


/*
  compare unique key for two rows

  TODO
    Add support for bit fields

  RETURN
    0   if both rows have equal unique value
    #   Rows are different
*/

int mi_unique_comp(MI_UNIQUEDEF *def, const uchar *a, const uchar *b,
                   my_bool null_are_equal)
{
  const uchar *pos_a, *pos_b, *end;
  HA_KEYSEG *keyseg;

  for (keyseg=def->seg ; keyseg < def->end ; keyseg++)
  {
    enum ha_base_keytype type=(enum ha_base_keytype) keyseg->type;
    uint a_length, b_length;
    a_length= b_length= keyseg->length;

    /* If part is NULL it's regarded as different */
    if (keyseg->null_bit)
    {
      uint tmp;
      if ((tmp=(a[keyseg->null_pos] & keyseg->null_bit)) !=
          (uint) (b[keyseg->null_pos] & keyseg->null_bit))
        return 1;
      if (tmp)
      {
        if (!null_are_equal)
          return 1;
        continue;
      }
    }
    pos_a= a+keyseg->start;
    pos_b= b+keyseg->start;
    if (keyseg->flag & HA_VAR_LENGTH_PART)
    {
      uint pack_length= keyseg->bit_start;
      if (pack_length == 1)
      {
        a_length= (uint) *(uchar*) pos_a++;
        b_length= (uint) *(uchar*) pos_b++;
      }
      else
      {
        a_length= uint2korr(pos_a);
        b_length= uint2korr(pos_b);
        pos_a+= 2;                              /* Skip VARCHAR length */
        pos_b+= 2;
      }
      set_if_smaller(a_length, keyseg->length); /* Safety */
      set_if_smaller(b_length, keyseg->length); /* safety */
    }
    else if (keyseg->flag & HA_BLOB_PART)
    {
      /* Only compare 'length' characters if length != 0 */
      a_length= _mi_calc_blob_length(keyseg->bit_start,pos_a);
      b_length= _mi_calc_blob_length(keyseg->bit_start,pos_b);
      /* Check that a and b are of equal length */
      if (keyseg->length)
      {
        /*
          This is used in some cases when we are not interested in comparing
          the whole length of the blob.
        */
        set_if_smaller(a_length, keyseg->length);
        set_if_smaller(b_length, keyseg->length);
      }
      memcpy(&pos_a, pos_a+keyseg->bit_start, sizeof(char*));
      memcpy(&pos_b, pos_b+keyseg->bit_start, sizeof(char*));
    }
    if (type == HA_KEYTYPE_TEXT || type == HA_KEYTYPE_VARTEXT1 ||
        type == HA_KEYTYPE_VARTEXT2)
    {
      if (ha_compare_text(keyseg->charset, (uchar *) pos_a, a_length,
                                           (uchar *) pos_b, b_length, 0, 1))
        return 1;
    }
    else
    {
      if (a_length != b_length)
        return 1;
      end= pos_a+a_length;
      while (pos_a != end)
      {
        if (*pos_a++ != *pos_b++)
          return 1;
      }
    }
  }
  return 0;
}