Roll Counting
-------------

This is how I propose to deal with the problem of pid wrapping. 

The problem:
------------
Although a pid uniquely identifies a process *at runtime*, it does
not uniquely identify it over the lifetime of a computing session.
pids eventually wrap around, and are reused. 

The solution:
-------------
I propose to add  another table to the event column, "rollcount", which 
will store the number of times that we have previously seen this pid. A 
process will be uniquely identified by its pid/rollcount. 

Implementation:
---------------
This should be done in post-processing - not while the system is actively
collecting data. Run this algorithm:

cur_count = "SELECT DISTINCT (pid) FROM event";
For each (item in cur_count):
	cur_forks = "SELECT * FROM event WHERE rc = cur_count.pid AND (it's a fork event) ORDER BY date";
	cur_count = 0;
	For each (fork in cur_forks):
		"UPDATE event SET roll_count = cur_count 
		 WHERE pid = fork.pid AND date >= fork.date"
		 cur_count ++;
	end
end