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by brian
clean slate |
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/* Copyright (C) 2000-2003 MySQL AB
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
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/*
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Functions for read record cacheing with myisam
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Used for reading dynamic/compressed records from datafile.
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Can fetch data directly from file (outside cache),
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if reading a small chunk straight before the cached part (with possible
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overlap).
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Can be explicitly asked not to use cache (by not setting READING_NEXT in
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flag) - useful for occasional out-of-cache reads, when the next read is
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expected to hit the cache again.
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Allows "partial read" errors in the record header (when READING_HEADER flag
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is set) - unread part is bzero'ed
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Note: out-of-cache reads are enabled for shared IO_CACHE's too,
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as these reads will be cached by OS cache (and my_pread is always atomic)
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*/
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#include "myisamdef.h" |
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int _mi_read_cache(IO_CACHE *info, uchar *buff, my_off_t pos, uint length, |
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int flag) |
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{
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uint read_length,in_buff_length; |
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my_off_t offset; |
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uchar *in_buff_pos; |
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DBUG_ENTER("_mi_read_cache"); |
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if (pos < info->pos_in_file) |
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{
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read_length=length; |
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if ((my_off_t) read_length > (my_off_t) (info->pos_in_file-pos)) |
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read_length=(uint) (info->pos_in_file-pos); |
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info->seek_not_done=1; |
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if (my_pread(info->file,buff,read_length,pos,MYF(MY_NABP))) |
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DBUG_RETURN(1); |
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if (!(length-=read_length)) |
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DBUG_RETURN(0); |
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pos+=read_length; |
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buff+=read_length; |
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}
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if (pos >= info->pos_in_file && |
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(offset= (my_off_t) (pos - info->pos_in_file)) < |
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(my_off_t) (info->read_end - info->request_pos)) |
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{
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in_buff_pos=info->request_pos+(uint) offset; |
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in_buff_length= min(length, (size_t) (info->read_end-in_buff_pos)); |
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memcpy(buff,info->request_pos+(uint) offset,(size_t) in_buff_length); |
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if (!(length-=in_buff_length)) |
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DBUG_RETURN(0); |
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pos+=in_buff_length; |
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buff+=in_buff_length; |
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}
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else
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in_buff_length=0; |
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if (flag & READING_NEXT) |
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{
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if (pos != (info->pos_in_file + |
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(uint) (info->read_end - info->request_pos))) |
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{
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info->pos_in_file=pos; /* Force start here */ |
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info->read_pos=info->read_end=info->request_pos; /* Everything used */ |
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info->seek_not_done=1; |
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}
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else
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info->read_pos=info->read_end; /* All block used */ |
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if (!(*info->read_function)(info,buff,length)) |
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DBUG_RETURN(0); |
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read_length=info->error; |
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}
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else
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{
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info->seek_not_done=1; |
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if ((read_length=my_pread(info->file,buff,length,pos,MYF(0))) == length) |
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DBUG_RETURN(0); |
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}
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if (!(flag & READING_HEADER) || (int) read_length == -1 || |
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read_length+in_buff_length < 3) |
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{
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DBUG_PRINT("error", |
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("Error %d reading next-multi-part block (Got %d bytes)", |
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my_errno, (int) read_length)); |
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if (!my_errno || my_errno == -1) |
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my_errno=HA_ERR_WRONG_IN_RECORD; |
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DBUG_RETURN(1); |
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}
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bzero(buff+read_length,MI_BLOCK_INFO_HEADER_LENGTH - in_buff_length - |
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read_length); |
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DBUG_RETURN(0); |
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} /* _mi_read_cache */ |