Conduit and PostgreSQL

For a while now I’ve been playing around with an event-drive software design (EDA) using conduit for processing of events. For this post the processing can basically be viewed as the following diagram

+-----------+   +------------+   +---------+
|           |   |            |   |         |
| PG source |-->| Processing |-->| PG sink |
|           |   |            |   |         |
+-----------+   +------------+   +---------+
     ^                                |
     |            +------+            |
     |            |      |            |
     |            |  PG  |            |
     +------------|  DB  |<-----------+
                  |      |
                  +------+

I started out looking for Conduit components for PostgreSQL on Hackage but failed to find something fitting so I started looking into writing them myself using postgresql-simple.

The sink wasn’t much of a problem, use await to get an event (a tuple) and write it to the database. My almost complete ignorance of using databases resulted in a first version of the source was rather naive and used busy-waiting. Then I stumbled on PostgreSQL’s support for notifications through the LISTEN and NOTIFY commands. I rather like the result and it seems to work well.1[]

It looks like this


  1. If I’ve missed something crucial I would of course love to hear about it.

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