Re: Perform streaming logical transactions by background workers and parallel apply

On Fri, Jul 22, 2022 at 8:27 AM wangw(dot)fnst(at)fujitsu(dot)com
<wangw(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Tues, Jul 19, 2022 at 10:29 AM I wrote:
> > Attach the news patches.
>
> Not able to apply patches cleanly because the change in HEAD (366283961a).
> Therefore, I rebased the patch based on the changes in HEAD.
>
> Attach the new patches.

+ /* Check the foreign keys. */
+ fkeys = RelationGetFKeyList(entry->localrel);
+ if (fkeys)
+ entry->parallel_apply = PARALLEL_APPLY_UNSAFE;

So if there is a foreign key on any of the tables which are parts of a
subscription then we do not allow changes for that subscription to be
applied in parallel? I think this is a big limitation because having
foreign key on the table is very normal right? I agree that if we
allow them then there could be failure due to out of order apply
right? but IMHO we should not put the restriction instead let it fail
if there is ever such conflict. Because if there is a conflict the
transaction will be sent again. Do we see that there could be wrong
or inconsistent results if we allow such things to be executed in
parallel. If not then IMHO just to avoid some corner case failure we
are restricting very normal cases.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com