Steve,
> mysql> create table t2 (c1 varchar(255));
> Query OK, 0 rows affected (0.00 sec)
> mysql> insert into t2 values ('s');
> Query OK, 1 row affected (0.00 sec)
> And this gave table status of
> Name: t2
> Type: MyISAM
> Row_format: Dynamic
> Rows: 1
> Avg_row_length: 20
Well, isn't the row length supposed to be 2 (not 20)? I mean 1 byte for
the character 's', plus 1 byte to store the length.
BTW, the manual doesn't say anything about "internal uses" of additional
bits/bytes, AFAIK. Thanks anyway.
Regards,
--
Stefan Hinz <hinz@stripped>
Geschäftsführer / CEO iConnect GmbH <http://iConnect.de>
Heesestr. 6, 12169 Berlin (Germany)
Tel: +49 30 7970948-0 Fax: +49 30 7970948-3
----- Original Message -----
From: "Steve Edberg" <sbedberg@stripped>
To: "Stefan Hinz" <hinz@stripped>
Cc: <mysql@stripped>
Sent: Wednesday, January 15, 2003 2:18 PM
Subject: Re: Avg_row_length
> Yep, you're right!
>
> Perhaps an extra byte is automatically reserved, not only for a
> null/not null status bit, but also for other internal use - eg; a
> 'row changed' bit, etc.
>
> I did a quick test:
>
> mysql> create table t2 (c1 varchar(255));
> Query OK, 0 rows affected (0.00 sec)
>
> mysql> insert into t2 values ('s');
> Query OK, 1 row affected (0.00 sec)
>
> And this gave table status of
>
> Name: t2
> Type: MyISAM
> Row_format: Dynamic
> Rows: 1
> Avg_row_length: 20
> Data_length: 20
> Max_data_length: 4294967295
> Index_length: 1024
> Data_free: 0
> Auto_increment: NULL
>
> so obviously the avg_row_length includes extra bytes for mysql
internal info.
>
> Learn something every day!
>
> -steve
>
>
> At 1:03 PM +0100 1/15/03, you wrote:
> >Steve,
> >
> >> I believe there is an extra byte for the 'null' flag; if you
declare
> >> this column to be NOT NULL, I'll bet the avg length will be 10.
> >
> >nice bet, but you lose <g>:
> >
> >mysql> DESCRIBE mynotnullisam;
> >+-------+----------+------+-----+---------+-------+
> >| Field | Type | Null | Key | Default | Extra |
> >+-------+----------+------+-----+---------+-------+
> >| col | char(10) | | | | |
> >+-------+----------+------+-----+---------+-------+
> >1 row in set (0.16 sec)
> >
> >mysql> SHOW TABLE STATUS LIKE 'mynotnullisam';
>
>+---------------+--------+------------+------+----------------+--------
-
> >----+
> >| Name | Type | Row_format | Rows | Avg_row_length |
> >Data_length |
>
>+---------------+--------+------------+------+----------------+--------
-
> >----+
> >| mynotnullisam | MyISAM | Fixed | 3 | 11 |
> >33 |
>
>+---------------+--------+------------+------+----------------+--------
-
> >----+
> >
>
>
> --
>
+-----------------------------------------------------------------------
-+
> | Steve Edberg
sbedberg@stripped |
> | University of California, Davis
(530)754-9127 |
> | Programming/Database/SysAdmin
http://pgfsun.ucdavis.edu/ |
>
+-----------------------------------------------------------------------
-+
> | SETI@Home: 1001 Work units on 23 oct 2002
|
> | 3.152 years CPU time, 3.142 years SETI user... and STILL no
aliens... |
>
+-----------------------------------------------------------------------
-+
