Re: Support ALTER SUBSCRIPTION ... ADD/DROP PUBLICATION ... syntax

> On Jan 27, 2021, at 19:41, Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> wrote:
> 
> On Wed, Jan 27, 2021 at 4:42 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>>> On Wed, Jan 27, 2021 at 3:16 PM Bharath Rupireddy
>>> <bharath.rupireddyforpostgres@gmail.com> wrote:
>>>> On Wed, Jan 27, 2021 at 3:01 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>>> So, I think the new syntax, ALTER SUBSCRIPTION .. ADD/DROP PUBLICATION
>>> will refresh the new and existing publications.
>> That sounds a bit unusual to me because when the user has specifically
>> asked to just ADD Publication, we might refresh some existing
>> Publication along with it?
> 
> Hmm. That's correct. I also feel we should not touch the existing
> publications, only the ones that are added/dropped should be
> refreshed. Because there will be an overhead of a SQL with more
> publications(in fetch_table_list) when AlterSubscription_refresh() is
> called with all the existing publications. We could just pass in the
> newly added/dropped publications to AlterSubscription_refresh().
> 
> I don't see any problem if ALTER SUBSCRIPTION ... ADD PUBLICATION with
> refresh true refreshes only the newly added publications, because what
> we do in AlterSubscription_refresh() is that we fetch the tables
> associated with the publications from the publisher, compare them with
> the previously fetched tables from that publication and add the new
> tables or remove the table that don't exist in that publication
> anymore.
> 
> For ALTER SUBSCRIPTION ... DROP PUBLICATION, also we can do the same
> thing i.e. refreshes only the dropped publications.
> 
> Thoughts?

Agreed. We just only need to refresh the added/dropped publications.  Furthermore, for publications that will be
dropped,we do not need the “copy_data” option, right?
 

-- 
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.