Re: Question on Hot Standby in PostgreSQL

On Wed, Nov 25, 2015 at 3:43 AM, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>
wrote:

> Alex Williams wrote:
> > Concerning these two params below, when using hot_standby_feedback,
> what would you set them if you
> > had the situation where you had queries constantly running on the
> standby, some quick and some long,
> > practically all day/night, everyday?
> >
> > max_standby_archive_delay (integer)
> > max_standby_streaming_delay (integer)
>
> > Should I still keep them as -1 (infinite)?
>
> I'd say set them both to 0.
>
> If you have hot_standby_feedback=on, the primary will not remove any rows
> still
> needed on the standby, so there should never be a need to delay WAL
> application.
>

hot_standby_feedback will significantly reduce the conflicts but it will
not totally eliminate them. For example if a new column is added to a
table, any query using this table on slave will be cancelled to apply this
change.

IF query cancellation is totally not acceptable then you will have to set
these delays to -1.

>
> The drawback is that you may get considerable bloat on the primary if many
> DELETE/UPDATE operation are going on and queries on the standby take a
> long time.
>
> Yours,
> Laurenz Albe
>