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From Cristian Dudila <cristian.dud...@keats-software.com>
Subject Re: rows locking in derby
Date Mon, 29 Jan 2007 14:32:43 GMT

Dyre.Tjeldvoll@Sun.COM wrote:
> Cristian Dudila <cristian.dudila@keats-software.com> writes:
> 
>> Hi,
>>
>>   We use derby for an application and we need to lock some rows. The
>> problem is that we would like to know if this rows are already locked.
>> Using TRANSACTION_REPEATABLE_READ we can lock this rows ( using SELECT
>> )but we don't know if this rows was already locked. Using "SELECT FOR
>> UPDATE" derby returns an exception that tell us that the row is
>> locked, but unfortunately ( for us ) we can lock only one row using
>> "SELECT FOR UPDATE".
> 
> I think it would be better if you could describe what it is you're
> trying to achieve. 
I want to warn the user if a row is locked in derby database by another 
user.
> 
>> Is there a possibility to lock multiple rows, using one connection and
>> to receive an exception or message ( from derby ) if this rows are
>> locked by somebody else before ?
> 
> Maybe I don't understand what you're trying to do, but in general it
> is not a good idea to use the database to communicate between
> threads. The database tries its best to hide the fact that other
> threads (connections) are accessing the data.
> 
With TRANSACTION_REPEATABLE_READ using a SELECT we will have a shared 
lock in derby, so we can read data but not to change it( in case of 
update, from another database connection, we receive an exception that 
the lock cannot be obtained ).
Is there a possibility to check in derby if a row is locked( except to 
try a dummy UPDATE on that row ) ?

Cristian

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