mi_rprev.cc

/* Copyright (c) 2000, 2025, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is designed to work with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have either included with
   the program or referenced in the documentation.

   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, version 2.0, 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 <sys/types.h>

#include "my_dbug.h"
#include "my_inttypes.h"
#include "storage/myisam/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;
  uint flag;
  MYISAM_SHARE *share = info->s;
  DBUG_TRACE;

  if ((inx = _mi_check_index(info, inx)) < 0) 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)) 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;
      set_my_errno(HA_ERR_END_OF_FILE);
      return 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) set_my_errno(HA_ERR_END_OF_FILE);
  } else if (!buf) {
    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 */
    return 0;
  }
  return my_errno();
} /* mi_rprev */