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help / color / mirror / Atom feedFrom: Amit Kapila <[email protected]>
To: Hayato Kuroda (Fujitsu) <[email protected]>
Cc: Vitaly Davydov <[email protected]>
Cc: Ajin Cherian <[email protected]>
Cc: Heikki Linnakangas <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: Slow catchup of 2PC (twophase) transactions on replica in LR
Date: Tue, 9 Jul 2024 10:35:37 +0530
Message-ID: <CAA4eK1Khy_YWFoQ1HOF_tGtiixD8YoTg86coX1-ckxt8vK3U=Q@mail.gmail.com> (raw)
In-Reply-To: <CAA4eK1+FRrL_fLWLsWQGHZRESg39ixzDX_S9hU8D7aFtU+a8uQ@mail.gmail.com>
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<[email protected]>
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<CAA4eK1+FRrL_fLWLsWQGHZRESg39ixzDX_S9hU8D7aFtU+a8uQ@mail.gmail.com>
On Mon, Jul 8, 2024 at 5:25 PM Amit Kapila <[email protected]> wrote:
>
>
> I see that in 0003/0004, the patch first aborts pending prepared
> transactions, update's catalog, and then change slot's property via
> walrcv_alter_slot. What if there is any ERROR (say the remote node is
> not reachable or there is an error while updating the catalog) after
> we abort the pending prepared transaction? Won't we end up with lost
> prepared transactions in such a case?
>
Considering the above is a problem the other possibility I thought of
is to change the order like abort prepared xacts after slot update.
That is also dangerous because any failure while aborting could make a
slot change permanent whereas the subscription option will still be
old value. Now, because the slot's two_phase property is off, at
commit, it can resend the entire transaction which can create a
problem because the corresponding prepared transaction will already be
present.
One more thing to think about in this regard is what if we fail after
aborting a few prepared transactions and not all?
At this stage, I am not able to think of a good solution for these
problems. So, if we don't get a solution for these, we can document
that users can first manually abort prepared transactions and then
switch off the two_phase option using Alter Subscription command.
--
With Regards,
Amit Kapila.
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To: [email protected]
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Subject: Re: Slow catchup of 2PC (twophase) transactions on replica in LR
In-Reply-To: <CAA4eK1Khy_YWFoQ1HOF_tGtiixD8YoTg86coX1-ckxt8vK3U=Q@mail.gmail.com>
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