Re: [HACKERS] Why does logical replication launcher set application_name?

On 6/6/17 15:58, Robert Haas wrote:
> The problem with the status quo (after Peter's commit) is that there's
> now nothing at all to identify the logical replication launcher, apart
> from the wait_event field, which is likely to be LogicalLauncherMain
> fairly often if you've got the launcher.  I don't personally see why
> we can't simply adopt Tom's original proposal of setting the query
> string to something like "<logical replication launcher>" which, while
> maybe not as elegant as providing some way to override the
> backend_type field, would be almost no work and substantially better
> for v10 than what we've got now.

The decision was made to add background workers to pg_stat_activity, but
no facility was provided to tell the background workers apart.  Is it
now the job of every background worker to invent a hack to populate some
other pg_stat_activity field with some ad hoc information?  What about
other logical replication worker types, parallel workers, external
background workers, auto-prewarm?

I think the bgw_type addition that I proposed nearby would solve this
quite well, but it needs a bit of work.  And arguably, it's too late for
PG10, but one could also argue that this is a design fault in the
pg_stat_activity extension that is valid to fix in PG10.