Faster distinct query?

SELECT station,array_agg(distinct(channel)) as channels FROM data GROUP BY station;

The explain execution plan can be found here:

and it looks pretty straight forward. It does an index_only scan, followed by an aggregate, to produce a result that is a list of stations along with a list of channels associated with each (there can be anywhere from 1 to 3 channels associated with each station). This query takes around 5 minutes to run.

To work around the issue, I created a materialized view that I can update periodically, and of course I can query said view in no time flat. However, I’m concerned that as the dataset grows, the time it takes to refresh the view will also grow (correct me if I am wrong there).

This is running PostgreSQL 13, and the index referenced is a two-column index on data(station, channel)