release/src/router/mysql/storage/myisam/mi_rprev.c

   1 /* Copyright (c) 2000, 2001, 2004-2007 MySQL AB
   2
   3    This program is free software; you can redistribute it and/or modify
   4    it under the terms of the GNU General Public License as published by
   5    the Free Software Foundation; version 2 of the License.
   6
   7    This program is distributed in the hope that it will be useful,
   8    but WITHOUT ANY WARRANTY; without even the implied warranty of
   9    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10    GNU General Public License for more details.
  11
  12    You should have received a copy of the GNU General Public License
  13    along with this program; if not, write to the Free Software
  14    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA */
  15
  16 #include "myisamdef.h"
  17
  18         /*
  19            Read previous row with the same key as previous read
  20            One may have done a write, update or delete of the previous row.
  21            NOTE! Even if one changes the previous row, the next read is done
  22            based on the position of the last used key!
  23         */
  24
  25 int mi_rprev(MI_INFO *info, uchar *buf, int inx)
  26 {
  27   int error,changed;
  28   register uint flag;
  29   MYISAM_SHARE *share=info->s;
  30   DBUG_ENTER("mi_rprev");
  31
  32   if ((inx = _mi_check_index(info,inx)) < 0)
  33     DBUG_RETURN(my_errno);
  34   flag=SEARCH_SMALLER;                          /* Read previous */
  35   if (info->lastpos == HA_OFFSET_ERROR && info->update & HA_STATE_NEXT_FOUND)
  36     flag=0;                                     /* Read last */
  37
  38   if (fast_mi_readinfo(info))
  39     DBUG_RETURN(my_errno);
  40   changed=_mi_test_if_changed(info);
  41   if (share->concurrent_insert)
  42     rw_rdlock(&share->key_root_lock[inx]);
  43   if (!flag)
  44     error=_mi_search_last(info, share->keyinfo+inx,
  45                           share->state.key_root[inx]);
  46   else if (!changed)
  47     error=_mi_search_next(info,share->keyinfo+inx,info->lastkey,
  48                           info->lastkey_length,flag,
  49                           share->state.key_root[inx]);
  50   else
  51     error=_mi_search(info,share->keyinfo+inx,info->lastkey,
  52                      USE_WHOLE_KEY, flag, share->state.key_root[inx]);
  53
  54   if (share->concurrent_insert)
  55   {
  56     if (!error)
  57     {
  58       while (info->lastpos >= info->state->data_file_length)
  59       {
  60         /* Skip rows that are inserted by other threads since we got a lock */
  61         if  ((error=_mi_search_next(info,share->keyinfo+inx,info->lastkey,
  62                                     info->lastkey_length,
  63                                     SEARCH_SMALLER,
  64                                     share->state.key_root[inx])))
  65           break;
  66       }
  67     }
  68     rw_unlock(&share->key_root_lock[inx]);
  69   }
  70   info->update&= (HA_STATE_CHANGED | HA_STATE_ROW_CHANGED);
  71   info->update|= HA_STATE_PREV_FOUND;
  72   if (error)
  73   {
  74     if (my_errno == HA_ERR_KEY_NOT_FOUND)
  75       my_errno=HA_ERR_END_OF_FILE;
  76   }
  77   else if (!buf)
  78   {
  79     DBUG_RETURN(info->lastpos==HA_OFFSET_ERROR ? my_errno : 0);
  80   }
  81   else if (!(*info->read_record)(info,info->lastpos,buf))
  82   {
  83     info->update|= HA_STATE_AKTIV;              /* Record is read */
  84     DBUG_RETURN(0);
  85   }
  86   DBUG_RETURN(my_errno);
  87 } /* mi_rprev */