On Wed, May 08, 2013 at 10:19:08AM +0200, Vincenzo Melandri wrote: > On Tue, May 7, 2013 at 11:55 PM, Robert Haas <robertmh...@gmail.com> wrote: > > This is a really hard problem. If you pick this as your first project > > hacking on PostgreSQL, you will almost certainly fail. > > > Thank you very much, i guessed that already -.- > Still, I needed that at my office for a long time, struggled with it many > times and had to come out with some "exotic" solutions... > Now I have spare time between projects, so I can work on it full-time. At > least it's worth a try, isn't it?
Well, you can work on it but I think it will be less programming and more coming up with a feasable solution. > Anyway, I'm working to better understand the problem, trying to identify at > least the main involved points. > At the moment I'm figuring out how the inherit mechanism works for > relations (in tablecmds.c).. Then I'll figure out about how indexes work.. While there are probably old threads in the archives, I find the easiest way to look at the problem is in the locking. In particular, I think if you can get unique indexes to work then the rest will follow. Consider the case of an inheritence hierarchy and you want a unique index on a column. Since you want to be able to create and drop children easily, each childs need to have an index just for them. But if you insert a row into one child you need to, somehow, prevent other people also inserting the same value in a different child. Efficiently and deadlock-free. This is hard, though we're up for crazy, out-of-the-box ideas. Note, there is one very special case, namely: - The children are used for partitioning. - The unique index you want is on the partition key. Since each value can only possibly appear in one table your locking problems vanish. The question is: how often does this happen? Hope this helps, -- Martijn van Oosterhout <klep...@svana.org> http://svana.org/kleptog/ > He who writes carelessly confesses thereby at the very outset that he does > not attach much importance to his own thoughts. -- Arthur Schopenhauer
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