| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Function to move the position of a replication slot |
| Date: | 2017-08-16 22:21:23 |
| Message-ID: | 30711.1502922083@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> Andres Freund wrote:
>> I think we should constrain the API to only allow later LSNs than
>> currently in the slot, rather than arbitrary ones. That's why I was
>> thinking of "forward". I'm not convinced it's a good / safe idea to
>> allow arbitrary values to be set.
> Hmm. In terms of safety, it is safe to move the LSN backwards, as long
> as the oldest LSN across all slots is not changed -- in other words, the
> actual safe limit is the oldest of all slot LSNs, rather than the
> current position of the slot being manipulated (which is what you're
> saying).
True, but you'd need to take some kind of global lock to verify that,
whereas "move forward only" would only need to examine/change the one
slot.
regards, tom lane
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