Re: BUG #8434: Why does dead lock occur many times ?

Hi Alvaro,

Thank you for finding it out!

I'll test it from now, so please
give me a while time.

regards,

(2013/11/28 1:42), Alvaro Herrera wrote:
> I think I have figured this out. This code was being too simplistic in
> that it was only checking whether there was a key-update or not; but
> that, it seems, is not sufficiently fine-grained. If we instead think
> in terms of an already-acquired MultiXactStatus, and a new
> MultiXactStatus corresponding to the lock we're trying to acquire, we
> can decide granularly whether each future version of the tuple can be
> locked by us or not. And if not, we can decide whether we need to wait
> on the transaction holding the lock, or fail if it already committed.
> (There is a funny trick here which is that we represent the held lock
> with a MultiXactStatus, even if the lock is only a plain Xid and not a
> multi. This doesn't seem a problem to me.)
>
> So I propose the attached patch. This doesn't change the behavior
> codified in the existing isolation tests, and it fixes my reduction of
> your original test case. (I haven't run your original test case yet,
> but I soon will.)
>
> Note: I don't quite like that this patch duplicates some code in
> compute_new_xmax_infomask() which determines the MultiXactStatus from
> the infomask bits. Not sure what a good refactoring is, though, because
> that code just issues a WARNING when the LOCK_ONLY bit is set and no
> other lockmode is set; whereas the new code issues an ERROR. It seems
> hard to justify doing otherwise in either place, though; and doing
> something more complicated doesn't seem warranted for such a corner
> case.
>
> Note: this patch doesn't apply to master in isolation. You will need
> the patch I mention in
>
http://www.postgresql.org/message-id/20131125201039.GF6597@eldon.alvh.no-ip.org
> even though I haven't posted it yet. Will do so shortly.
>