maria-discuss team mailing list archive

[Tom Worster <fsb@xxxxxxxxxx>]

who is truncating columns?

On 3/1/15, 3:27 PM, "Sergei Golubchik" <serg@xxxxxxxxxxx> wrote:

>Hi, Tom!
>
>On Mar 01, Tom Worster wrote:
>> I discovered this showstopper on Friday while working with real data in
>> development of a new app. I managed to narrow it down today and filed
>>the
>> bug report.
>> 
>> https://mariadb.atlassian.net/browse/MDEV-7650
>> 
>> Looks like Maria saves an illegally formatted dyncol string if a dynamic
>> column is longer than 64kB and is not alphabetically last by name among
>>the
>> dynamic column in the blob.
>> 
>> Tbh, even is this were fixed tomorrow so I could proceed with my work,
>>I'm
>> not sure I would use dyncols. My confidence in the feature has been
>>shaken.
>> It's a pity because the Active Record ORM extension I wrote was working.
>
>You could've paid attention to warnings from your test case:
>
>===========
>MariaDB [test]> insert into t (a, b, dcols) values (1, 'two',
>column_create('one', 1, 'css', @txt));
>Query OK, 1 row affected, 1 warning (0.00 sec)
>
>Warning (Code 1265): Data truncated for column 'dcols' at row 1
>===========
>
>Indeed, blob size is limited by 64K. Another test case for your bug is:
>
>===========
>MariaDB [test]> select length(column_create('one', 1, 'txt', @txt));
>+----------------------------------------------+
>| length(column_create('one', 1, 'css', @txt)) |
>+----------------------------------------------+
>|                                        65563 |
>+----------------------------------------------+
>1 row in set (0.00 sec)
>
>MariaDB [test]> select column_check(left(column_create('one', 1, 'txt',
>@txt), 65535));
>+-----------------------------------------------------------------+
>| column_check(left(column_create('one', 1, 'txt', @txt), 65535)) |
>+-----------------------------------------------------------------+
>|                                                               1 |
>+-----------------------------------------------------------------+
>1 row in set (0.00 sec)
>
>MariaDB [test]> select column_check(left(column_create('one', 1, 'css',
>@txt), 65535));
>+-----------------------------------------------------------------+
>| column_check(left(column_create('one', 1, 'css', @txt), 65535)) |
>+-----------------------------------------------------------------+
>|                                                               0 |
>+-----------------------------------------------------------------+
>1 row in set (0.00 sec)
>===========
>
>So the bug is that column_check() doesn't always detects that the dyncol
>was truncated.
>
>Either way, even if column_check() returns 1, you probably shouldn't
>use truncated dynamic columns in your application :)
>
>Use LONGBLOB instead.
>
>Regards,
>Sergei
>