troubleshooting 8.1.2

We have 4 8.1.2 cluster running on an HP-UX 11.23 Itanium, repeatedly
dying with the following log message:

2006-07-11 12:52:27 EDT [21582] LOG: received fast shutdown request
2006-07-11 12:52:27 EDT [21591] LOG: shutting down
2006-07-11 12:52:27 EDT [21591] LOG: database system is shut down
2006-07-11 12:52:27 EDT [21584] LOG: logger shutting down

We can't figure out why it is shutting down. Nobody here is sending
the signal. We don't have any cron jobs doing that sort of thing.

We've also seen out of memory errors when this first started
happening, though glance had not shown GBL_MEM_UTIL above 90% (with
OS buffer cache max/min percents at 10%/3%). The box has 64gb of
RAM, so that would seem to mean there was ~6GB of RAM available
when it got the out of memory errors.

Just in case, we shutdown several clusters, and restarted them, and
now even with plentiful memory, they're dying with the same message.

Any ideas?

Ed