Re: idle_in_transaction_timeout

On 2014-06-29 15:48:15 -0400, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > On Sun, Jun 29, 2014 at 12:32 PM, Kevin Grittner <kgrittn@ymail.com> wrote:
> >> I propose to push this as it stands except for the postgres_fdw
> >> part.  The default is easy enough to change if we reach consensus,
> >> and expanding the scope can be a new patch in a new CF.
> >> Objections?
> 
> > Yeah, I think someone should do some analysis of whether this is
> > adding gettimeofday() calls, and how many, and what the performance
> > implications are.
> 
> I believe that as the patch stands, we'd incur one new gettimeofday()
> per query-inside-a-transaction, inside the enable_timeout_after() call.
> (I think the disable_timeout() call would not result in a gettimeofday
> call, since there would be no remaining live timeout events.)
> 
> We could possibly refactor enough to share the clock reading with the call
> done in pgstat_report_activity.  Not sure how ugly that would be or
> whether it's worth the trouble.  Note that in the not-a-transaction-block
> case, we already have got two gettimeofday calls in this sequence, one in
> pgstat_report_stat and one in pgstat_report_activity :-(

I've seen several high throughput production servers where code around
gettimeofday is in the top three profile entries - so I'd be hesitant to
add more there. Especially as the majority of people here seems to think
we should enable this by default.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services