On Fri, Dec 30, 2011 at 10:00:50AM +0000, Fabio Sangiovanni wrote: > Ok I'm kind of a newbie here :) > My understanding of the problem is: > if I have 2 threads, running at the same time, both of them executing the > same SQL transaction (made up of more select or update queries), how can I > predict which one is executed first? It's just like you said: I'd need the > whole thing to happen in a single inter-thread transaction :) > The solution, for now, is limiting Lua sessions to 1 lowering the total > number of threads to 1. > > Fabio > > Il giorno 30/dic/2011, alle ore 10:32, Nils Breunese (Lemonbit) ha scritto: > > > Fabio Sangiovanni wrote: > > > >> Database transactions help in terms of integrity, but they can do nothing > >> about the order of data updates. If 2 threads work independently and > >> execute the same update query on the db, I can't predict with certainty > >> which one will occur first. > > > > AFAIK no updates are committed until the transaction is committed, so all > > queries within a transaction are guaranteed to happen as if they were one > > modification to the database. If the order of transactions is important > > then I think you might need to rethink your logic, because then the whole > > thing would need to happen in a transaction. I'm not sure what you're > > trying to do exactly, but it sounds like transactions should be able to > > help here. > > > > Nils. > >
I can't help wondering if what you are doing is going to look like UPDATE stats SET counter = counter + 1 WHERE foo = 'bar' If so, you shouldn't have any issues with concurrency afaik. Running Lua SQL script in "high traffic site" however is probably not a very good idea due to aforementioned perfomance issues. Aki Tuomi
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