Hello,
  Forgive me for reporting this on the behalf of some other developers, I will gather more details as needed.

But the basic problem we're having is with a query that:

   - is always fast the first time ( < 3 seconds )
   - is very slow the following time, when using a connection pool (~ 30 seconds)
   - is pretty fast the following time, when not using a connection pool (5 or 6 seconds)

This is even on a single DB with no other load.

It's a fairly complicated query with sub queries, grouping, and such.
I've been told it creates two temp tables.

I know this is not a whole lot to go one - but are there any pointer for connection pool vs no connection pool on a lightly loaded DB?

This was actually tried and reproduced with multiple connection pools - hikari-db, c3p0, and apache connection pool.

Take care,
  -stu