On Tue, 6 Oct 2009, Brandon Hume wrote:
You're running a large process on a low-memory machine. I strongly suspect CentOS isn't giving slapd enough time to shut down properly.
I think you've hit this head on. The only other suggestion I might make is to consider the checkpointing configuration as described in slapd-bdb(5) man page. As a rule of thumb, more frequent checkpoints mean that the time to flush at shutdown is decreased.