Re: [GENERAL] 9.4.1 -> 9.4.2 problem: could not access status of transaction 1

Andres Freund wrote:
> On June 8, 2015 7:06:31 PM GMT+02:00, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:

> >I might be misreading the code, but PMSIGNAL_START_AUTOVAC_LAUNCHER
> >only causes things to happen (i.e. a new worker to be started) when
> >autovacuum is disabled. If autovacuum is enabled, postmaster
> >receives the signal and doesn't do anything about it, because the
> >launcher is already running. Of course, regularly scheduled autovac
> >workers will eventually start running, but perhaps this is not good
> >enough.
>
> Well that's just the same for the plain xid precedent? I'd not mind
> improving further, but that seems like a separate thing.

Sure. I just concern that we might be putting excessive trust on
emergency workers being launched at a high pace. With normally
configured systems (naptime=1min) it shouldn't be a problem, but we have
seen systems with naptime set to one hour or so, and those might feel
some pain; and it would get worse the more databases you have, because
people might feel the need to space the autovac runs even more.

(My personal alarm bells go off when I see autovac_naptime=15min or
more, but apparently not everybody sees things that way.)

> ---
> Please excuse brevity and formatting - I am writing this on my mobile phone.

I wonder if these notices are useful at all.

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services