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help / color / mirror / Atom feedFrom: Bertrand Drouvot <[email protected]>
To: Amit Kapila <[email protected]>
Cc: Bharath Rupireddy <[email protected]>
Cc: shveta malik <[email protected]>
Cc: Nathan Bossart <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Introduce XID age and inactive timeout based replication slot invalidation
Date: Fri, 29 Mar 2024 06:19:05 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAA4eK1JU14-Fz3Ttx_wy=vzDaeTSv=umt7sC3N+4k2aYcdk4=w@mail.gmail.com>
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Hi,
On Fri, Mar 29, 2024 at 09:39:31AM +0530, Amit Kapila wrote:
> On Wed, Mar 27, 2024 at 9:00 PM Bharath Rupireddy
> <[email protected]> wrote:
> >
> >
> > Thanks. I'm attaching v29 patches. 0001 managing inactive_since on the
> > standby for sync slots.
> >
>
> Commit message states: "why we can't just update inactive_since for
> synced slots on the standby with the value received from remote slot
> on the primary. This is consistent with any other slot parameter i.e.
> all of them are synced from the primary."
>
> The inactive_since is not consistent with other slot parameters which
> we copy. We don't perform anything related to those other parameters
> like say two_phase phase which can change that property. However, we
> do acquire the slot, advance the slot (as per recent discussion [1]),
> and release it. Since these operations can impact inactive_since, it
> seems to me that inactive_since is not the same as other parameters.
> It can have a different value than the primary. Why would anyone want
> to know the value of inactive_since from primary after the standby is
> promoted?
I think it can be useful "before" it is promoted and in case the primary is down.
I agree that tracking the activity time of a synced slot can be useful, why
not creating a dedicated field for that purpose (and keep inactive_since a
perfect "copy" of the primary)?
> Now, the other concern is that calling GetCurrentTimestamp()
> could be costly when the values for the slot are not going to be
> updated but if that happens we can optimize such that before acquiring
> the slot we can have some minimal pre-checks to ensure whether we need
> to update the slot or not.
Right, but for a very active slot it is likely that we call GetCurrentTimestamp()
during almost each sync cycle.
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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Subject: Re: Introduce XID age and inactive timeout based replication slot invalidation
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