mi_rprev.c
上传用户:romrleung
上传日期:2022-05-23
资源大小:18897k
文件大小:3k
- /* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
- 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; either version 2 of the License, or
- (at your option) any later version.
- 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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 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, byte *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)
- rw_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 (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;
- }
- }
- rw_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 */