The cause of the database corruption that I was observing has, with a fair degree of certainty, been identified, and I can sum it up in one word: hardware The server on which I was doing the load apparently has a really subtle bug where it will randomly and only occasionally write a single bad byte to disk. So a large database load had a high probability of getting hit. I began to suspect this when I discovered that various system binaries (the date command, lynx) were failing with odd error messages (bad syscall, for example). Yet the system mostly ran just fine... I redid the database load on new hardware, and things have been working perfectly. (Can you imagine what would have happened had this hardware been used for its usual market: Windows or NT? I could realize this was hardware because system binaries in FreeBSD just don't fail like that. But if it were Windows, one would doubtless just reinstall, and the problem would go away, only to crop up in some *other* binary later...) I'm very relieved to be able to report that I have *not* found a data corruption problem with the ZODB!! --RDM