Asked what the distinction actually is, and the SQL half needed correcting
first: under exclusive ownership SQL runs against your own database and nothing
else, whatever transport a query might travel over. Both options are the mesh's
own channel and both ride the broker, so the transport is not the distinction.
The distinction is where the answer lives when you need it. A request asks at
the moment and waits — always current, costs a round trip, cannot answer when
the other side is down. A subscription keeps a local copy — instant, works
offline, as current as the last event received, and you must handle what you
missed.
What decides is not taste. ADR 0036 makes disconnection an ordinary situation
rather than an exception, so anything that must keep working while disconnected
CANNOT use a request: there is nobody to ask. And the converse — anything where
a stale answer is worse than no answer cannot use a subscription. A display can
lag; a decision about whether a grant is still valid cannot.
So an apparently open question turns out to be derived from a decision already
taken. What stays open is narrower: what a consumer does about the events it
missed while disconnected — replay from a point, ask once for a full picture and
resume, or rebuild. The question every projection has.
Also recorded: separate databases are required in the new design, and the shared
registry is a leftover rather than a pattern.
jschoubben
e71d532c2e