Some nsf files missing after restart

We received Out of virtual memory message so restarted the server. Then found that few so far 2 nsf files (mail and mail-in) disappeared. No trace of them after restart. Those was there just before restarting according to the log.nsf.

What could cause such problem?

Subject: What Does The Log Show?

Does the log file on the Domino Server show anything related to the missing files or show any messages related to a database recovery or fixup notice?