Hi!
On Sep 07, Hagen H?pfner wrote:
>
> (1) The state-part of the header contains a version number (first 4
> bytes). Is this the version number of the MyISAM driver? I currently use
> MySQL 5.0.4beta where the version is 0xFE FE 07 01.
No, it's just to mean "this is MYI file".
> (2) The next part (2 Bytes) of the header includes options like
> HA_OPTION_PACK_RECORD ... Are these options the values defined in my_base.h:
>
> /* optionbits for database */
> #define HA_OPTION_PACK_RECORD 1
dynamic row format
> #define HA_OPTION_PACK_KEYS 2
It doesn't do anything in MyISAM, as far as I can see.
> #define HA_OPTION_COMPRESS_RECORD 4
Data file is compressed with myisampack
> #define HA_OPTION_LONG_BLOB_PTR 8 /* new ISAM format */
According to this part from mi_open():
if (share->options &
~(HA_OPTION_PACK_RECORD | HA_OPTION_PACK_KEYS |
HA_OPTION_COMPRESS_RECORD | HA_OPTION_READ_ONLY_DATA |
HA_OPTION_TEMP_COMPRESS_RECORD | HA_OPTION_CHECKSUM |
HA_OPTION_TMP_TABLE | HA_OPTION_DELAY_KEY_WRITE))
{
DBUG_PRINT("error",("wrong options: 0x%lx", share->options));
my_errno=HA_ERR_OLD_FILE;
goto err;
}
HA_OPTION_LONG_BLOB_PTR is apparently not used in MyISAM :)
> #define HA_OPTION_TMP_TABLE 16
MyISAM assumes this table is not used by other threads - disables
locking, disables concurrent insert support, does not update table's
header, etc.
> #define HA_OPTION_CHECKSUM 32
Maintain table's checksum - update it after all inserts/deletes/updates.
> #define HA_OPTION_DELAY_KEY_WRITE 64
see DELAY_KEY_WRITE in the CREATE TABLE page on the manual.
> #define HA_OPTION_NO_PACK_KEYS 128 /* Reserved for MySQL */
According to the code snippet above, this option is not used in MyISAM.
> #define HA_OPTION_TEMP_COMPRESS_RECORD ((uint) 16384) /* set by isamchk */
it's only used for 'myisamchk --unpack'
> #define HA_OPTION_READ_ONLY_DATA ((uint) 32768) /* Set by isamchk */
Table is readonly.
Usually it's set on open, not written in the file:
if (mode == O_RDONLY || options & HA_OPTION_COMPRESS_RECORD)
options|=HA_OPTION_READ_ONLY_DATA;
> If so, what does these options stand for?
>
> (3) What is the different between the key_parts and unique_key_parts?
The same difference as betweek 'key' and 'unique', MI_KEYDEF and
MI_UNIQUEDEF. 'key' is the regular index, including UNIQUE index.
'unique' is an index over a hashed value of included columns. It's used
to maintain unique constraint over a set of columns that is longer than
a regular key can support. Currently it's only used internally in
temporary tables for SELECT DISTINCT.
> (4) What is the "language" of an index?
collation.
Regards,
Sergei
--
__ ___ ___ ____ __
/ |/ /_ __/ __/ __ \/ / Sergei Golubchik <serg@stripped>
/ /|_/ / // /\ \/ /_/ / /__ MySQL AB, Senior Software Developer
/_/ /_/\_, /___/\___\_\___/ Kerpen, Germany
<___/ www.mysql.com
