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help / color / mirror / Atom feedFrom: Yura Sokolov <[email protected]>
To: Dilip Kumar <[email protected]>
To: Kyotaro Horiguchi <[email protected]>
Cc: Julien Rouhaud <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Subject: Re: Error "initial slot snapshot too large" in create replication slot
Date: Sun, 13 Feb 2022 17:35:38 +0300
Message-ID: <[email protected]> (raw)
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В Пн, 07/02/2022 в 13:52 +0530, Dilip Kumar пишет:
> On Mon, Jan 31, 2022 at 11:50 AM Kyotaro Horiguchi
> <[email protected]> wrote:
> > At Mon, 17 Jan 2022 09:27:14 +0530, Dilip Kumar <[email protected]> wrote in
> >
> > me> Mmm. The size of the array cannot be larger than the numbers the
> > me> *Connt() functions return. Thus we cannot attach the oversized array
> > me> to ->subxip. (I don't recall clearly but that would lead to assertion
> > me> failure somewhere..)
> >
> > Then, I fixed the v3 error and post v4.
>
> Yeah you are right, SetTransactionSnapshot() has that assertion.
> Anyway after looking again it appears that
> GetMaxSnapshotSubxidCount is the correct size because this is
> PGPROC_MAX_CACHED_SUBXIDS +1, i.e. it considers top transactions as
> well so we don't need to add them separately.
>
> > SnapBUildInitialSnapshot tries to store XIDS of both top and sub
> > transactions into snapshot->xip array but the array is easily
> > overflowed and CREATE_REPLICATOIN_SLOT command ends with an error.
> >
> > To fix this, this patch is doing the following things.
> >
> > - Use subxip array instead of xip array to allow us have larger array
> > for xids. So the snapshot is marked as takenDuringRecovery, which
> > is a kind of abuse but largely reduces the chance of getting
> > "initial slot snapshot too large" error.
>
> Right. I think the patch looks fine to me.
>
Good day.
I've looked to the patch. Personally I'd prefer dynamically resize
xip array. But I think there is issue with upgrade if replica source
is upgraded before destination, right?
Concerning patch, I think more comments should be written about new
usage case for `takenDuringRecovery`. May be this field should be renamed
at all?
And there are checks for `takenDuringRecovery` in `heapgetpage` and
`heapam_scan_sample_next_tuple`. Are this checks affected by the change?
Neither the preceding discussion nor commit message answer me.
-------
regards
Yura Sokolov
Postgres Professional
[email protected]
[email protected]
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