From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
---|---|
To: | "Hayato Kuroda (Fujitsu)" <kuroda(dot)hayato(at)fujitsu(dot)com> |
Cc: | Vitaly Davydov <v(dot)davydov(at)postgrespro(dot)ru>, Ajin Cherian <itsajin(at)gmail(dot)com>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: Slow catchup of 2PC (twophase) transactions on replica in LR |
Date: | 2024-07-09 05:05:37 |
Message-ID: | CAA4eK1Khy_YWFoQ1HOF_tGtiixD8YoTg86coX1-ckxt8vK3U=Q@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
On Mon, Jul 8, 2024 at 5:25 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> 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.
From | Date | Subject | |
---|---|---|---|
Next Message | Michael Paquier | 2024-07-09 05:16:13 | Re: Injection point locking |
Previous Message | Ahmed Yarub Hani Al Nuaimi | 2024-07-09 04:58:02 | Lock-free compaction. Why not? |