Обсуждение: Performance differences between fdw and view+fdw

Hello all,

I'm trying to understand a behavior I'm currently seeing while testing mongo's fdw (using the mongo-c-driver 1.0 version).

Say I have a foreign table with 50 columns and 14000 rows, I also have a view that does basically the same thing as querying the foreign table directly except for  a few castings.

Working with the foreign table directly, a query like select * from foreign_table takes like 7 seconds, doing the same query but against the view takes like 8.5 seconds

Another example, a select * from foreign_table where col = 'something' takes like 12 ms but doing the same against the view takes like 110ms.

The only thing I could put the blame on when using the view is that inside is the same query as working with the foreign table but I use casts for a few columns like select col::text from foreign_table...

I don't know if anyone has tried mongo_fdw or something similar but I would like to know if this behavior is normal and more importantly why the view seems inefficient compared to query the foreign table directly (and without casts)

Thanks in advance!!