diff options
Diffstat (limited to 'storage/myisam/mi_cache.c')
| -rw-r--r-- | storage/myisam/mi_cache.c | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/storage/myisam/mi_cache.c b/storage/myisam/mi_cache.c new file mode 100644 index 00000000..9a6c4044 --- /dev/null +++ b/storage/myisam/mi_cache.c @@ -0,0 +1,109 @@ +/* Copyright (c) 2000-2003, 2005-2007 MySQL AB, 2009 Sun Microsystems, Inc. + Use is subject to license terms. + + 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; version 2 of the License. + + 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 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 mysql_file_pread is always atomic) +*/ + +#include "myisamdef.h" + +int _mi_read_cache(IO_CACHE *info, uchar *buff, my_off_t pos, size_t length, + int flag) +{ + size_t read_length,in_buff_length; + my_off_t offset; + uchar *in_buff_pos; + DBUG_ENTER("_mi_read_cache"); + DBUG_ASSERT(!(info->myflags & MY_ENCRYPT)); + + 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=(size_t)(info->pos_in_file-pos); + info->seek_not_done=1; + if (mysql_file_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= MY_MIN(length, (size_t)(info->read_end-in_buff_pos)); + memcpy(buff,info->request_pos+(uint) offset, 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 (!_my_b_read(info,buff,length)) + DBUG_RETURN(0); + read_length=info->error; + } + else + { + info->seek_not_done=1; + if ((read_length= mysql_file_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_FILE_TOO_SHORT) + 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 */ |