| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com> |
| Cc: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, amit(dot)kapila16(at)gmail(dot)com, michael(at)paquier(dot)xyz, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: min_safe_lsn column in pg_replication_slots view |
| Date: | 2020-06-24 15:15:14 |
| Message-ID: | 20200624151514.GA17861@alvherre.pgsql |
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| Lists: | pgsql-hackers |
On 2020-Jun-24, Fujii Masao wrote:
> On 2020/06/24 8:39, Alvaro Herrera wrote:
> > I think we should publish the value from wal_keep_segments separately
> > from max_slot_wal_keep_size. ISTM that the user might decide to change
> > or remove wal_keep_segments and be suddenly at risk of losing slots
> > because of overlooking that it was wal_keep_segments, not
> > max_slot_wal_keep_size, that was protecting them.
>
> You mean to have two functions that returns
>
> 1. "current WAL LSN - wal_keep_segments * 16MB"
> 2. "current WAL LSN - max_slot_wal_keep_size"
Hmm, but all the values there are easily findable. What would be the
point in repeating it?
Maybe we should disregard this line of thinking and go back to
Horiguchi-san's original proposal, to wit use the "distance to
breakage", as also supported now by Amit Kapila[1] (unless I
misunderstand him).
[1] https://postgr.es/m/CAA4eK1L2oJ7T1cESdc5w4J9L3Q_hhvWqTigdAXKfnsJy4=v13w@mail.gmail.com
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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