It looks like the default thread stack is not large enough for MySQL 4.1
on Linux running on AMD64.
With NPTL, the database quickly crashed after a few hours of heavy load
(segv).
Without NTPL, I believed it wasn't the case. But after one week mysqld
process were stuck in a strange state. They weren't doing anything, just as
if they were waiting for a dead lock.
It didn't happen with MySQL 4.0 on the same hardware.
Bumping up the thread stack to 256 K seems to fix the issue, both with and
without NPTL.
Best regards,
-Frank.