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110 lines
3.7 KiB
C
110 lines
3.7 KiB
C
/* Copyright (c) 2000-2003, 2005-2007 MySQL AB, 2009 Sun Microsystems, Inc.
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Use is subject to license terms.
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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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 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 mysql_file_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 (mysql_file_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= mysql_file_pread(info->file, buff, length, pos,
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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 */
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