Hi! I did a look at the patch, like the idea. The overall code is in a good condition, implements the described feature.
Side note: this is not a problem of this particular patch, but in pg_stat_get_subscription and many other places, there is a switch with worker types. Can we use a default section there to have an explicit error instead of the compiler warnings if somehow we decide to add another one worker type? So, should we mark this thread as RfC? -- Best regards, Maxim Orlov.
