Re: Add two missing tests in 035_standby_logical_decoding.pl

Hi,

On 4/25/23 6:23 AM, Amit Kapila wrote:
> On Mon, Apr 24, 2023 at 3:36 PM Drouvot, Bertrand
> <bertranddrouvot.pg@gmail.com> wrote:
>>
>> Without the second "pg_log_standby_snapshot()" then wait_for_subscription_sync() would be waiting
>> some time on the poll for "SELECT count(1) = 0 FROM pg_subscription_rel WHERE srsubstate NOT IN ('r', 's');"
>>
>> Adding a comment in V3 to explain the need for the second pg_log_standby_snapshot().
>>
> 
> Won't this still be unpredictable because it is possible that the
> tablesync worker may take more time to get launched or create a
> replication slot? If that happens after your second
> pg_log_standby_snapshot() then wait_for_subscription_sync() will be
> hanging. 

Oh right, that looks like a possible scenario.

> Wouldn't it be better to create a subscription with
> (copy_data = false) to make it predictable and then we won't need
> pg_log_standby_snapshot() to be performed twice?
> 
> If you agree with the above suggestion then you probably need to move
> wait_for_subscription_sync() before Insert.
> 

I like that idea, thanks! Done in V4 attached.

Not related to the above corner case, but while re-reading the patch I also added:

"
$node_primary->wait_for_replay_catchup($node_standby);
"

between the publication creation on the primary and the subscription to the standby
(to ensure the publication gets replicated before we request for the subscription creation).

Regards,

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