Re: POSIX pthread counter (integer) overflow in valgrind drd_vc.c

 > drd: drd_vc.c:96 (vgDrd_vc_increment): Assertion 'oldcount <
 > vc->vc[i].count' failed.

I suspect (I don't know for sure) that this is a vector clock overflow.
That might happen if your program performed more that 2^32 inter-thread
synchronisation events, for example, mutex lock, unlock, condvar posts
or signals, sem post/wait, thread create/join, etc.  Is that likely?

Can you reduce the problem size (to perhaps a few hundred thousand records)
and see if the failure goes away?

 > I don't understand what the semantics of the thread counter "count" is [..]

I suspect that is incremented every time one of the abovementioned thread
events happens.  The mechanism is a bit complex, but a counter overflow could
happen if there is a chain of such thread events (possibly involving multiple
threads) that is more than 2^32 long.

J