Re: Lock ACCESS EXCLUSIVE and Select question !

Yep i already have those columns and unique constraint, my issue isn't sell
the seat two times, i was a lot of paranoiac about that and use a lock mode
to restricted for that.
I will check if i can create rows for seats before sell and use update, so i
can use SELECT FOR UPDATE and not use insert, having to lock the whole table
to check if a seat is free or sold, but i have to solve several issues in
the meantime, for example, to sell a seat for one month in future, will i
have to create every single seat(row) in database to be able to know if is
free or sold, and other stuff, even so, seems a new and good idea for me, is
the first time i heard about SELECT FOR UPDATE.

Another question !, can i combine SELECT FOR UPDATE and LOCK command on
different tables at the same transaction ?

Alan Acosta

On Tue, Mar 1, 2011 at 9:33 AM, Andrew Sullivan <ajs(at)crankycanuck(dot)ca> wrote:

> On Tue, Mar 01, 2011 at 09:23:49AM -0500, Alan Acosta wrote:
>
> > seats have an specific bus even 5 minutes before departure, sometimes i
> know
> > sometimes i don't, even sometimes when i know i have to change on fly
> this
> > capacity, for example my bus crash just before departure, so i have to
> use a
> > default averaged capacity. A human must have the final word about which
> bus
> > departure, so the software must be very very open to changes.
>
> This still sounds a little odd to me, but there is another way to do
> it, and someone suggested it in this thread. If you're doing this
> only with INSERT, then you just need to find some combination of
> columns that needs to be unique (one of which is obviously the seat
> number). Then you'll get a unique violation when two people try to
> insert the same data, and someone will lose.
>
> Your application could catch this in a savepoint and try again with a
> different seat number.
>
> A
>
> --
> Andrew Sullivan
> ajs(at)crankycanuck(dot)ca
>
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