Re: Strange Windows problem, lock_timeout test request

2013-03-06 19:53 keltezéssel, Tom Lane írta:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Wed, Feb 27, 2013 at 8:58 AM, Stephen Frost <sfrost@snowman.net> wrote:
>>> It's still entirely possible to get 99% done and then hit that last
>>> tuple that you need a lock on and just tip over the lock_timeout_stmt
>>> limit due to prior waiting and ending up wasting a bunch of work, hence
>>> why I'm not entirely sure that this is that much better than
>>> statement_timeout.
>> I tend to agree that this should be based on the length of any
>> individual lock wait, not the cumulative duration of lock waits.
>> Otherwise, it seems like it'll be very hard to set this to a
>> meaningful value.  For example, if you set this to 1 minute, and that
>> means the length of any single wait, then you basically know that
>> it'll only kick in if there is some other, long-running transaction
>> that's holding the lock.  But if it means the cumulative length of all
>> waits, it's not so clear, because now you might also have this kick in
>> if you wait for 100ms on 600 different occasions.  In other words,
>> complex queries that lock or update many tuples may get killed even if
>> they never wait very long at all for any single lock.  That seems like
>> it will be almost indistinguishable from random, unprincipled query
>> cancellations.
> Yeah.  I'm also unconvinced that there's really much use-case territory
> here that statement_timeout doesn't cover well enough.  To have a case
> that statement-level lock timeout covers and statement_timeout doesn't,
> you need to suppose that you know how long the query can realistically
> wait for all locks together, but *not* how long it's going to run in the
> absence of lock delays.  That seems a bit far-fetched, particularly when
> thinking of row-level locks, whose cumulative timeout would presumably
> need to scale with the number of rows the query will visit.
>
> If statement-level lock timeouts were cheap to add, that would be one
> thing; but given that they're complicating the code materially, I think
> we need a more convincing argument for them.

OK, so it's not wanted. Surprise, surprise, it was already dropped
from the patch. Can you _please_ review the last patch and comment
on it instead of the state of past?

Thanks and best regards,
Zoltán Böszörményi

>
>             regards, tom lane
>
>


--
----------------------------------
Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
Gröhrmühlgasse 26
A-2700 Wiener Neustadt, Austria
Web: http://www.postgresql-support.de     http://www.postgresql.at/