From: | Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> |
---|---|
To: | dilipbalaut(at)gmail(dot)com |
Cc: | andres(at)anarazel(dot)de, jchampion(at)timescale(dot)com, y(dot)sokolov(at)postgrespro(dot)ru, rjuju123(at)gmail(dot)com, pgsql-hackers(at)lists(dot)postgresql(dot)org |
Subject: | Re: Error "initial slot snapshot too large" in create replication slot |
Date: | 2022-09-13 06:22:37 |
Message-ID: | 20220913.152237.338218493796303493.horikyota.ntt@gmail.com |
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Lists: | pgsql-hackers |
Thanks for raizing this up, Robert and the comment, Andres.
At Tue, 13 Sep 2022 07:00:42 +0530, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote in
> On Tue, Sep 13, 2022 at 3:22 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> >
> > It's not obvious to me that it's the right design (or even correct) to ask
> > reorderbuffer about an xid being a subxid. Maybe I'm missing something, but
> > why would reorderbuffer even be guaranteed to know about all these subxids?
>
> Yeah, you are right, the reorderbuffer will only know about the
> transaction for which changes got added to the reorder buffer. So
> this seems not to be the right design idea.
That function is called after the SnapBuild reaches
SNAPBUILD_CONSISTENT state ,or SnapBuildInitialSnapshot() rejects
other than that state. That is, IIUC the top-sub relationship of all
the currently running transactions is fully known to reorder buffer.
We need a comment about that.
> > I wonder if a better fix here wouldn't be to allow importing a snapshot with a
> > larger ->xid array. Yes, we can't do that in CurrentSnapshotData, but IIRC we
> > need to be in a transactional snapshot anyway, which is copied anyway?
>
> Yeah when I first found this issue, I thought that should be the
> solution. But later it went in a different direction.
I think that that is the best solution if rbtxn_is_known_subxzact() is
known to be unreliable at the time.
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
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