[cstreit]

Wayne... Often when there is not a proper index on a table, it will build temporary versions of it (smaller) to do full table scans or build temp indexes.

I don't know what db you are using, but temp tablespaces are also used in sorting activity as well, also related to indexes.

In this case the query is SELECT DISTINCT post.userid,
thread.threadid,thread.threadid So you could try adding an index on Post.userid and Thread.threadid.?

THat's a weird query though, because it selects threadid twice...