After a file is created, LSM server threads open the file, causing some internal pages to be preloaded before updating the LSM tree.

However, we now sweep the session's handle cache, and these handles would appear "dead" and thus be closed if a sweep happened in between.

Idea 1: turn off handle sweeps and see what happens to the LSM performance after merges

Idea 2: Timestamp the last close of a handle, ignore them in sweep if they are less than N seconds old (e.g., N=30).