| From: | Simon Riggs <simon(dot)riggs(at)2ndquadrant(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Craig Ringer <craig(at)2ndquadrant(dot)com>, Thom Brown <thom(at)linux(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Logical decoding on standby |
| Date: | 2017-03-22 15:59:42 |
| Message-ID: | CANP8+jL2QLMqRpkTkEA0FDLZSOu4mUz6+ouiKM4nOs1ctD2T2A@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 22 March 2017 at 13:06, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> The parts I think are important for Pg10 are:
>
>> * Ability to create logical slots on replicas
>
> Doesn't this also imply recovery conflicts on DROP DATABASE?
Not needed until the slot is in use, which is a later patch.
> Besides,
> allowing to drop all slots using a database upon DROP DATABASE, is a
> useful thing on its own.
Sure but that's a separate feature unrelated to this patch and we're
running out of time.
>> * Ability to advance (via feedback or via SQL function) - no need to
>> actually decode and call output plugins at al
>
> That pretty much requires decoding, otherwise you really don't know how
> much WAL you have to retain.
Knowing how much WAL to retain is key.
Why would decoding tell you how much WAL to retain?
We tried to implement this automatically from the master, which was
rejected. So the only other way is manually. We need one or the other.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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