RE: [PATCH] Preserve replication origin OIDs in pg_upgrade

Dear Amit,

> Fair point but isn't it sufficient to check the tracked_origins rather
> than all origins? In docs of max_active_replication_origins, we say:
> "Setting it to a lower value than the current number of tracked
> replication origins (reflected in pg_replication_origin_status) will
> prevent the server from starting." which suggests here we should have
> a tight check of tracked_origins against
> max_active_replication_origins.

Basically it sounds good, but it can slightly change the behavior if the old node
has some subscriptions which have never been enabled. Till now, we just counted
the number of subscriptions, thus we took into account them [1]. But after the
patch they can be ignored; IIUC pg_upgrade can succeed in the case.

If the change is OK, we can proceed with your (and Shlok-san's) idea.

[1]: reproducer is below.
1. initialized old node with max_active_replication_origins=1
2. created two subscriptions with (connect=false)
3. initialized new node with max_active_replication_origins=1
4. ran pg_upgrade and it did error-out

```
$ pg_upgrade -b /usr/local/pgsql/bin/ -d old/ -D new/ -U postgres
Performing Consistency Checks
-----------------------------
...
Checking new cluster configuration for subscriptions
"max_active_replication_origins" (1) must be greater than or equal to the number of subscriptions (2) in the old cluster
Failure, exiting
```

Best regards,
Hayato Kuroda
FUJITSU LIMITED