Re: Restricting maximum keep segments by repslots

At Wed, 1 Mar 2017 08:06:10 -0800, Andres Freund <andres(at)anarazel(dot)de> wrote in <20170301160610(dot)wc7ez3vihmialntd(at)alap3(dot)anarazel(dot)de>
> On 2017-02-28 12:42:32 +0900, Michael Paquier wrote:
> > Please no. Replication slots are designed the current way because we
> > don't want to have to use something like wal_keep_segments as it is a
> > wart, and this applies as well for replication slots in my opinion.
>
> I think a per-slot option to limit the amount of retention would make
> sense.

I started from that but I found that all slots refer to the same
location as the origin of the distance, that is, the last segment
number that KeepLogSeg returns. As the result the whole logic
became as the following. This is one reason of the proposed pach.

- Take the maximum value of the maximum-retain-LSN-amount per slot.
- Apply the maximum value during the calcuation in KeepLogSeg.
- (These steps runs only when at least one slot exists)

The another reason was, as Robert retold, I thought that this is
a matter of system (or a DB cluster) wide health and works in a
bit different way from what the name "max_wal_size_hard"
suggests.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center