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From: Peter Eisentraut <[email protected]>
To: Bharath Rupireddy <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: Re: Synchronizing slots from primary to standby
Date: Tue, 14 Dec 2021 23:24:02 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <CALj2ACUGNGfWRtwwZwT-Y6feEP8EtOMhVTE87rdeY14mBpsRUA@mail.gmail.com>
References: <[email protected]>
	<CALj2ACUGNGfWRtwwZwT-Y6feEP8EtOMhVTE87rdeY14mBpsRUA@mail.gmail.com>

On 28.11.21 07:52, Bharath Rupireddy wrote:
> 1) Instead of a new LIST_SLOT command, can't we use
> READ_REPLICATION_SLOT (slight modifications needs to be done to make
> it support logical replication slots and to get more information from
> the subscriber).

I looked at that but didn't see an obvious way to consolidate them. 
This is something we could look at again later.

> 2) How frequently the new bg worker is going to sync the slot info?
> How can it ensure that the latest information exists say when the
> subscriber is down/crashed before it picks up the latest slot
> information?

The interval is currently hardcoded, but could be a configuration 
setting.  In the v2 patch, there is a new setting that orders physical 
replication before logical so that the logical subscribers cannot get 
ahead of the physical standby.

> 3) Instead of the subscriber pulling the slot info, why can't the
> publisher (via the walsender or a new bg worker maybe?) push the
> latest slot info? I'm not sure we want to add more functionality to
> the walsender, if yes, isn't it going to be much simpler?

This sounds like the failover slot feature, which was rejected.

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