mi_cache.c
上传用户:romrleung
上传日期:2022-05-23
资源大小:18897k
文件大小:4k
- /* 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 */
- /*
- Functions for read record cacheing with myisam
- Used for reading dynamic/compressed records from datafile.
- Can fetch data directly from file (outside cache),
- if reading a small chunk straight before the cached part (with possible
- overlap).
- Can be explicitly asked not to use cache (by not setting READING_NEXT in
- flag) - useful for occasional out-of-cache reads, when the next read is
- expected to hit the cache again.
- Allows "partial read" errors in the record header (when READING_HEADER flag
- is set) - unread part is bzero'ed
- Note: out-of-cache reads are enabled for shared IO_CACHE's too,
- as these reads will be cached by OS cache (and my_pread is always atomic)
- */
- #include "myisamdef.h"
- int _mi_read_cache(IO_CACHE *info, byte *buff, my_off_t pos, uint length,
- int flag)
- {
- uint read_length,in_buff_length;
- my_off_t offset;
- char *in_buff_pos;
- DBUG_ENTER("_mi_read_cache");
- if (pos < info->pos_in_file)
- {
- read_length=length;
- if ((my_off_t) read_length > (my_off_t) (info->pos_in_file-pos))
- read_length=(uint) (info->pos_in_file-pos);
- info->seek_not_done=1;
- if (my_pread(info->file,buff,read_length,pos,MYF(MY_NABP)))
- DBUG_RETURN(1);
- if (!(length-=read_length))
- DBUG_RETURN(0);
- pos+=read_length;
- buff+=read_length;
- }
- if (pos >= info->pos_in_file &&
- (offset= (my_off_t) (pos - info->pos_in_file)) <
- (my_off_t) (info->read_end - info->request_pos))
- {
- in_buff_pos=info->request_pos+(uint) offset;
- in_buff_length= min(length,(uint) (info->read_end-in_buff_pos));
- memcpy(buff,info->request_pos+(uint) offset,(size_t) in_buff_length);
- if (!(length-=in_buff_length))
- DBUG_RETURN(0);
- pos+=in_buff_length;
- buff+=in_buff_length;
- }
- else
- in_buff_length=0;
- if (flag & READING_NEXT)
- {
- if (pos != (info->pos_in_file +
- (uint) (info->read_end - info->request_pos)))
- {
- info->pos_in_file=pos; /* Force start here */
- info->read_pos=info->read_end=info->request_pos; /* Everything used */
- info->seek_not_done=1;
- }
- else
- info->read_pos=info->read_end; /* All block used */
- if (!(*info->read_function)(info,buff,length))
- DBUG_RETURN(0);
- read_length=info->error;
- }
- else
- {
- info->seek_not_done=1;
- if ((read_length=my_pread(info->file,buff,length,pos,MYF(0))) == length)
- DBUG_RETURN(0);
- }
- if (!(flag & READING_HEADER) || (int) read_length == -1 ||
- read_length+in_buff_length < 3)
- {
- DBUG_PRINT("error",
- ("Error %d reading next-multi-part block (Got %d bytes)",
- my_errno, (int) read_length));
- if (!my_errno || my_errno == -1)
- my_errno=HA_ERR_WRONG_IN_RECORD;
- DBUG_RETURN(1);
- }
- bzero(buff+read_length,MI_BLOCK_INFO_HEADER_LENGTH - in_buff_length -
- read_length);
- DBUG_RETURN(0);
- } /* _mi_read_cache */