LISTEN/NOTIFY Is it possible?

[txbm]

Is it possible to execute! a LISTEN statement and have the callback be invoked asynchronously for new values? Or anyway of doing this?

Nice work by the way. Works well for everything else I'm doing.

[alaisi]

Hi,

short answer: not yet, long answer: yes and no.

The underlying Java library supports LISTEN, and you can access it directly as the object returned by open-db is a Listenable.

However, this hasn't added to the clojure driver (or documented) as the LISTEN/NOTIFY support is not yet reliable in the sense that if the connection is broken/closed due to e.g. a network glitch, the listening stops. The listener has no reliable way of detecting this and resubscribing so the events stop flowing.

The current horrible workaround would be to create a pool with a single connection only, checking out that connection, adding a listener and then running healthchecks on the connection.

[txbm]

@alaisi Haha, I ended up discovering all that the hard way :) Ended up creating a dedicated LISTEN service that uses psycopg2 as it has more mature support for this feature and it replicates the PG mutations onto a Kafka topic which my Clojure service then consumes from. A bit of a wild work-around for the moment but my attempts to create a reliable LISTEN/NOTIFY setup using Java/Clojure proved fruitless. Anyway, appreciate you taking the time to confirm your experience and I look forward to future support. Thanks again.