Re: Hot Standby Feedback should default to on in 9.3+

On Fri, Nov 30, 2012 at 6:20 PM, Kevin Grittner <kgrittn@mail.com> wrote:
> Claudio Freire wrote:
>
>>> With what setting of max_standby_streaming_delay? I would rather
>>> default that to -1 than default hot_standby_feedback on. That
>>> way what you do on the standby only affects the standby.
>>
>> 1d
>
> Was there actually a transaction hanging open for an entire day on
> the standby? Was it a query which actually ran that long, or an
> ill-behaved user or piece of software?

No, and if there was, I wouldn't care for it to be cancelled.

Queries were being cancelled way before that timeout was reached,
probably something to do with max_keep_segments on the master side
being unable to keep up for that long.

> I have most certainly managed databases where holding up vacuuming
> on the source would cripple performance to the point that users
> would have demanded that any other process causing it must be
> immediately canceled. And canceling it wouldn't be enough at that
> point -- the bloat would still need to be fixed before they could
> work efficiently.

I wouldn't mind occasional cancels, but these were recurring. When a
query ran long enough, there was no way for it to finish, no matter
how many times you tried. The master never stops being busy, that's
probably a factor.