Re: Request: pg_cancel_backend variant that handles 'idle in transaction' sessions

Dne 5.11.2015 19:02 napsal uživatel "Merlin Moncure" <mmoncure(at)gmail(dot)com>:
>
> On Wed, Nov 4, 2015 at 4:15 PM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> > * Joshua D. Drake (jd(at)commandprompt(dot)com) wrote:
> >> On 11/04/2015 01:55 PM, Stephen Frost wrote:
> >> >* Joe Conway (mail(at)joeconway(dot)com) wrote:
> >> >>On 11/04/2015 01:24 PM, Alvaro Herrera wrote:
> >> >>>I agree with Pavel. Having a transaction timeout just does not
make any
> >> >>>sense. I can see absolutely no use for it. An idle-in-transaction
> >> >>>timeout, on the other hand, is very useful.
> >> >>
> >> >>+1 -- agreed
> >> >
> >> >I'm not sure of that. I can certainly see a use for transaction
> >> >timeouts- after all, they hold locks and can be very disruptive in the
> >> >long run. Further, there are cases where a transaction is normally
very
> >> >fast and in a corner case it becomes extremely slow and disruptive to
> >> >the rest of the system. In those cases, having a timeout for it is
> >> >valuable.
> >>
> >> Yeah but anything holding a lock that long can be terminated via
> >> statement_timeout can it not?
> >
> > Well, no? statement_timeout is per-statement, while transaction_timeout
> > is, well, per transaction. If there's a process which is going and has
> > an open transaction and it's holding locks, that can be an issue.
> >
> > To be frank, my gut feeling is that transaction_timeout is actually more
> > useful than statement_timeout.
>
> Exactly. statement_timeout is weak because it resets for every
> statement regardless of transaction. Similarly, pg_cancel_backend is
> weak because it only works if a backend is actually in statement
> regardless of transaction state (reading this thread, it's clear that
> this is not widely known even among -hackers which further reinforces
> the point).
>
> Thus, I think we have consensus that transaction_timeout is good -- it
> would deprecate statement_timeout essentially. Likewise,
> pg_cancel_transaction is good and would deprecate pg_cancel_backend;
> it's hard for me to imagine a scenario where a user would call
> pg_cancel_backend if pg_cancel_transaction were to be available.
>

I am sorry, I see a consensus between you and Stephen only.

Regards

Pavel
> merlin