Re: old_snapshot_threshold's interaction with hash index

On Tue, May 3, 2016 at 9:47 PM, Kevin Grittner <kgrittn(at)gmail(dot)com> wrote:
>
> On Tue, May 3, 2016 at 11:09 AM, Robert Haas <robertmhaas(at)gmail(dot)com>
wrote:
> > On Tue, May 3, 2016 at 11:46 AM, Kevin Grittner <kgrittn(at)gmail(dot)com>
wrote:
> >>> Uh, I have no idea how this would be fixed if the PageLSN is zero. Do
> >>> you?
> >>
> >> Yes, I see three ways, the most obvious of which is what Amit
> >> suggested -- don't do early vacuum on a table which has a hash index.
> >
> > What do you mean by "early VACUUM"?
>
> Both vacuuming and hot-pruning adjust xmin based on calling
> TransactionIdLimitedForOldSnapshots(TransactionId recentXmin,
> Relation relation). I'm talking about having that function, if all
> other conditions for the override pass, checking for a hash index,
> too.
>
> > Amit suggested disabling
> > HOT-pruning, but HOT-pruning happens completely outside of VACUUM. It
> > also happens inside VACUUM, so if we disabled HOT pruning, how could
> > we VACUUM at all? Sorry, I am confused.
>
> I guess we were both talking a bit loosely since (as I mentioned
> above) the function that adjusts the xmin is called for a vacuum or
> pruning. He mentioned one and I mentioned the other, but it's all
> controlled by TransactionIdLimitedForOldSnapshots().
>

Yes, I think we are saying the same thing here.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com