Re: [HACKERS] logical decoding of two-phase transactions

On 30/03/18 00:30, Petr Jelinek wrote:
> On 29/03/18 23:58, Andres Freund wrote:
>> On 2018-03-29 23:52:18 +0200, Tomas Vondra wrote:
>>>> I have added details about this in src/backend/storage/lmgr/README as
>>>> suggested by you.
>>>>
>>>
>>> Thanks. I think the README is a good start, but I think we also need to
>>> improve the comments, which is usually more detailed than the README.
>>> For example, it's not quite acceptable that LogicalLockTransaction and
>>> LogicalUnlockTransaction have about no comments, especially when it's
>>> meant to be public API for decoding plugins.
>>
>> FWIW, for me that's ground to not accept the feature. Burdening output
>> plugins with this will make their development painful (because they'll
>> have to adapt regularly) and correctness doubful (there's nothing
>> checking for the lock being skipped). Another way needs to be found.
>>
>
> I have to agree with Andres here. It's also visible in the latter
> patches. The pgoutput patch forgets to call these new APIs completely.
> The test_decoding calls them, but it does so even when it's processing
> changes for committed transaction.. I think that should be avoided as it
> means potentially doing SLRU lookup for every change. So doing it right
> is indeed not easy.

Ah turns out it actually does not need SLRU lookup in this case (I
missed the reorder buffer call), so I take that part back.

--
Petr Jelinek http://www.2ndQuadrant.com/
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