I tried to limit the amount of rows returned by adding

...
   where 
        received_at >= current_date - interval '2 years'
...

to my query. This caused the optimiser to start using an index on received_at and also to lengthen the duration of the query 10-fold….

Here are the explain plans:

• Explain plan query without filter
• Explain plan query with filter

The query that starts using the Index is starting to do a lot of IO.

What is causing this?

What is the best next action?

Using PostgreSQL 15.