RE: Conflict detection for update_deleted in logical replication

On Tue, Jun 24, 2025 at 6:22 PM shveta malik wrote:
>
> On Mon, Jun 23, 2025 at 4:20 PM Zhijie Hou (Fujitsu)
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> >
> > Here is the V40 patch set
>
> Thanks for the patches. Few comments:
>
> 1)
> In get_subscription_info(), we are doing COUNT of rci-subscriptions using
> below query:
> SELECT count(*) AS nsub, COUNT(CASE WHEN subretainconflictinfo THEN 1
> END) AS retain_conflict_info FROM pg_catalog.pg_subscription;
>
> And then we are doing:
> cluster->sub_retain_conflict_info = (strcmp(PQgetvalue(res, 0,
> i_retain_conflict_info), "1") == 0);
>
> i.e. get the value and compare with "1". If the count of such subs is say 2,
> won't it fail and will set sub_retain_conflict_info as 0?

Right, it could return wrong results. I have changed it to count(*) xx > 0
so that it can return directly boolean value.

>
> 2)
> create_logical_replication_slots(void)
> {
> + if (!count_old_cluster_logical_slots())
> + return;
> +
>
> We shall get rid of count_old_cluster_logical_slots() here as the caller is
> checking it already.

Removed.

>
> 3)
> We can move the 'old_cluster.sub_retain_conflict_info' check from
> create_conflict_detection_slot() to its caller. Then it will be more informative
> and consistent with how we check migrate_logical_slots outside of
> create_conflict_detection_slot()

Moved.

Here is the V41 patch set which includes the following changes:

0001:
* Rebased due to recent commit fd51941.
* Addressed the comments above.
* Improved some documentation stuff.
* Improved the status message when creating
conflict detection slot in pg_upgrade

0002:
No change

0003:
No change

0004:
No change

0005:
No change

0006:
Rebased due to recent commit fd51941.

Best Regards,
Hou zj