Re: DROP SUBSCRIPTION and ROLLBACK

On 08/02/17 07:40, Masahiko Sawada wrote:
> On Wed, Feb 8, 2017 at 9:01 AM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com> wrote:
>> On Wed, Feb 8, 2017 at 1:30 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>>> On Wed, Feb 8, 2017 at 12:26 AM, Petr Jelinek
>>> <petr(dot)jelinek(at)2ndquadrant(dot)com> wrote:
>>>> For example what happens if apply crashes during the DROP
>>>> SUBSCRIPTION/COMMIT and is not started because the delete from catalog
>>>> is now visible so the subscription is no longer there?
>>>
>>> Another idea is to treat DROP SUBSCRIPTION in the same way as VACUUM, i.e.,
>>> make it emit an error if it's executed within user's transaction block.
>>
>> It seems to me that this is exactly Petr's point: using
>> PreventTransactionChain() to prevent things to happen.
>
> Agreed. It's better to prevent to be executed inside user transaction
> block. And I understood there is too many failure scenarios we need to
> handle.
>
>>> Also DROP SUBSCRIPTION should call CommitTransactionCommand() just
>>> after removing the entry from pg_subscription, then connect to the publisher
>>> and remove the replication slot.
>>
>> For consistency that may be important.
>
> Agreed.
>
> Attached patch, please give me feedback.
>

This looks good (and similar to what initial patch had btw). Works fine
for me as well.

Remaining issue is, what to do about CREATE SUBSCRIPTION then, there are
similar failure scenarios there, should we prevent it from running
inside transaction as well?

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