mi_rprev.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 */

#include "myisamdef.h"

        /*
           Read previous row with the same key as previous read
           One may have done a write, update or delete of the previous row.
           NOTE! Even if one changes the previous row, the next read is done
           based on the position of the last used key!
        */

int mi_rprev(MI_INFO *info, uchar *buf, int inx)
{
  int error,changed;
  register uint flag;
  MYISAM_SHARE *share=info->s;
  DBUG_ENTER("mi_rprev");

  if ((inx = _mi_check_index(info,inx)) < 0)
    DBUG_RETURN(my_errno);
  flag=SEARCH_SMALLER;                          /* Read previous */
  if (info->lastpos == HA_OFFSET_ERROR && info->update & HA_STATE_NEXT_FOUND)
    flag=0;                                     /* Read last */

  if (fast_mi_readinfo(info))
    DBUG_RETURN(my_errno);
  changed=_mi_test_if_changed(info);
  if (share->concurrent_insert)
    mysql_rwlock_rdlock(&share->key_root_lock[inx]);
  if (!flag)
    error=_mi_search_last(info, share->keyinfo+inx,
                          share->state.key_root[inx]);
  else if (!changed)
    error=_mi_search_next(info,share->keyinfo+inx,info->lastkey,
                          info->lastkey_length,flag,
                          share->state.key_root[inx]);
  else
    error=_mi_search(info,share->keyinfo+inx,info->lastkey,
                     USE_WHOLE_KEY, flag, share->state.key_root[inx]);

  if (!error)
  {
    int res= 0;
    while ((share->concurrent_insert && 
            info->lastpos >= info->state->data_file_length) ||
           (info->index_cond_func &&
            !(res= mi_check_index_cond(info, inx, buf))))
    {
      /* 
         Skip rows that are either inserted by other threads since
         we got a lock or do not match pushed index conditions
      */
      if  ((error=_mi_search_next(info,share->keyinfo+inx,info->lastkey,
                                  info->lastkey_length,
                                  SEARCH_SMALLER,
                                  share->state.key_root[inx])))
        break;
    }
    if (!error && res == 2) 
    {
      if (share->concurrent_insert)
        mysql_rwlock_unlock(&share->key_root_lock[inx]);
      info->lastpos= HA_OFFSET_ERROR;
      DBUG_RETURN(my_errno= HA_ERR_END_OF_FILE);
    }
  }

  if (share->concurrent_insert)
  {
    if (!error)
    {
      while (info->lastpos >= info->state->data_file_length)
      {
        /* Skip rows that are inserted by other threads since we got a lock */
        if  ((error=_mi_search_next(info,share->keyinfo+inx,info->lastkey,
                                    info->lastkey_length,
                                    SEARCH_SMALLER,
                                    share->state.key_root[inx])))
          break;
      }
    }
    mysql_rwlock_unlock(&share->key_root_lock[inx]);
  }

  info->update&= (HA_STATE_CHANGED | HA_STATE_ROW_CHANGED);
  info->update|= HA_STATE_PREV_FOUND;
  if (error)
  {
    if (my_errno == HA_ERR_KEY_NOT_FOUND)
      my_errno=HA_ERR_END_OF_FILE;
  }
  else if (!buf)
  {
    DBUG_RETURN(info->lastpos==HA_OFFSET_ERROR ? my_errno : 0);
  }
  else if (!(*info->read_record)(info,info->lastpos,buf))
  {
    info->update|= HA_STATE_AKTIV;              /* Record is read */
    DBUG_RETURN(0);
  }
  DBUG_RETURN(my_errno);
} /* mi_rprev */