Re: Minimal logical decoding on standbys

Hi,

On 1/16/23 3:28 PM, Drouvot, Bertrand wrote:
> Hi,
>
> On 1/13/23 10:17 AM, Drouvot, Bertrand wrote:
>> Hi,
>>
>> On 1/11/23 9:27 PM, Andres Freund wrote:
>>> Hi,
>>>
>>> On 2023-01-06 10:52:06 +0100, Drouvot, Bertrand wrote:
>>>
>>> The problem I have with that is that I saw a lot of flakiness in the tests due
>>> to the race condition. So introducing them in that order just doesn't make a
>>> whole lot of sense to me.
>>
>> You are right it does not make sense to introduce fixing the race condition after the TAP tests
>> and after introducing the decoding logic. I'll reorder the sub-patches.
>>
>
> V40 attached is changing the sub-patches ordering.
>
>>> The suggested path in earlier versions to avoid doing so was to make sure that
>>> we pass down the Relation for the table into the necessary functions. Did you
>>> explore that any further?
>>
>> So, for gistXLogPageReuse() and _bt_delitems_delete() this is "easy" to pass the Heap Relation.
>> This is what was done in earlier versions of this patch series.
>>
>> But we would need to define a way to propagate the Heap Relation for those 2 functions:
>>
>> _bt_log_reuse_page()
>> vacuumRedirectAndPlaceholder()
>>
>
> V40 is getting rid of the new indisusercatalog field in pg_index and is passing the
> heap relation all the way down to _bt_log_reuse_page() and vacuumRedirectAndPlaceholder() instead
> (and obviously to gistXLogPageReuse() and _bt_delitems_delete() too).
>
> Remarks:
>
> 1) V40 adds the heap relation in the IndexVacuumInfo and ParallelVacuumState structs. It is used
> for the _bt_log_reuse_page() and vacuumRedirectAndPlaceholder() cases where I did not find any place
> where to get the heap relation from in the existing code path.
>
> 2) V40 adds a "real" heap relation to all the _bt_getbuf() calls. Another option could have been
> to add it only for the code paths leading to _bt_log_reuse_page() but I thought it is cleaner to
> do it for all of them.
>
>> I will give it another look, also because I just realized that it could be beneficial
>> for vacuumRedirectAndPlaceholder() too, as per this comment:
>>
>> "
>>      /* XXX: providing heap relation would allow more pruning */
>>      vistest = GlobalVisTestFor(NULL);
>> "
>
> Now, we could also pass the heap relation to GlobalVisTestFor() in vacuumRedirectAndPlaceholder().
> Could be done in or independently of this patch series once committed (it's not part of V40).

Please find attached V41, tiny rebase due to 47bb9db759.

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com