Most of the queries against CONTENT table use 'lower' db function for a title field. The goes for (space) key field in SPACES table.
We do it to make a case insensitive comparison, however it means that db2 does not use the existing indexes for those fields and performs a full table scan.
This results in a poor performance.

This can be applicable to other database too, but it is not verified. Also other databases may have global 'case sensitivity' flag.