[Zope] Concurrency/Atomicity in ZSQL/ZOracleDA ?

[Renaud Guérin]

> > The trouble is, I need to generate this id in the first place, and as
> I said I'd
> > rather not use a sequence. Thus the max(id)+1
> I would not do this. It makes life more complicated. Why not use a 
> sequence? Then you are guaranteed atomicy. I am no Oracle expert, but 
> other database I have used let you retreive the next number in the 
> sequence (before the row has been added) while simultaneously locking 
> the table against other inserts for the duration of the transaction.

I have very limited rights on the DB right now, and in particular I can't create
sequences or other objects! Asking for this permission would probably smash my
deadline :(
Hence my looking for a reasonably safe alternative.

> > But what I want to make sure is that a transaction implies atomic
> operation, ie
> > nobody else can perform another select max(id)+1 before the select of
> the first
> > caller is performed.
> > Is that OK with my current setup ?
> No, if you must do this then you will need to explicitly lock the table
> against inserts *before* you look up the next id (you can use the lock
> SQL statement for this). Then if another thread does the same operation
> concurrently, one will block the other and they will be executed 
> serially instead of in parallel.

I think I need to lock the table against reads, not inserts.
What I must ensure is that no more select's max(id)+1 can be done before the
subsequent insert is completed.
I don't know how to use LOCK to do that, anyone ?

thanks


--
Software is like sex : it's better when it's free
	-- Linus Torvalds
http://renaudguerin.com
--