To exclude the version with inbound parameter (and too big data in selected field), I modified the query as:

"with st as (select * from prod.stocks limit 1) select json_agg(row_to_json(st)) #>> '{}' from st"

The error remained the same

I'm sure the problem is in a selected field. The warehouse has a varchar type on the database side and %String on the IRIS side. It's just a warehouse ID. I need to select a big JSON string as one field, one record.

I could go with this problem to the database team, but in external SQL console with the same driver (I used SQuirreL SQL) all works fine.

My main hypothesis is that there is some error on the Java Gateway level. But I don't understand what the Long type value means here. Long, it's a number, right? Selected field have type text.