On a big mdl_files table (802530 records), get_recent_files() function utilizes an SQL query that works extremely slow under PostgreSQL, eating up a huge amount of CPU resources and RAM. If the same query is split into several queries which use a TEMP table instead of nested SELECT, it works perfect. I can demonstrate a patch if needed, but I think you guys get the idea.

The issue occurs with Moodle 2.3.2, but the query is exactly the same in the latest version I see on Github. Is there a reason it can't be made working with a TEMP table instead?