Re: logical decoding of two-phase transactions

On 31 Jan. 2017 22:43, "Konstantin Knizhnik" <k(dot)knizhnik(at)postgrespro(dot)ru>
wrote:

On 31.01.2017 09:29, Michael Paquier wrote:

> On Fri, Jan 27, 2017 at 8:52 AM, Craig Ringer <craig(at)2ndquadrant(dot)com>
> wrote:
>
>> Now, if it's simpler to just xlog the gid at COMMIT PREPARED time when
>> wal_level >= logical I don't think that's the end of the world. But
>> since we already have almost everything we need in memory, why not
>> just stash the gid on ReorderBufferTXN?
>>
> I have been through this thread... And to be honest, I have a hard
> time understanding for which purpose the information of a 2PC
> transaction is useful in the case of logical decoding. The prepare and
> commit prepared have been received by a node which is at the root of
> the cluster tree, a node of the cluster at an upper level, or a
> client, being in charge of issuing all the prepare queries, and then
> issue the commit prepared to finish the transaction across a cluster.
> In short, even if you do logical decoding from the root node, or the
> one at a higher level, you would care just about the fact that it has
> been committed.
>

in any state. So there three records in the WAL: PREPARE, PRECOMMIT,
COMMIT_PREPARED and
recovery can involve either all of them, either PRECOMMIT+COMMIT_PREPARED
either just COMMIT_PREPARED.

That's your modified Pg though.

This 2pc logical decoding patch proposal is for core and I think it just
confused things to introduce discussion of unrelated changes made by your
product to the codebase.

--
Konstantin Knizhnik

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