<p>Now I know that bigint is 2^64; that is, more atoms than there are in the known universe.  I shouldn't be worried, as my mere human brain simply can't get around the enormity of that number.</p>

<p>However, let's say that I record every change to every category, product and order in my system, from launch until the end of time.  Should I be concerned about the performance of table writes before I worry about running out of primary key values?  Should I record events of different priorities to different event tables?  Will I run out of atoms on a hard drive before I run out of bigints?  How big should I let an event log table get before I start archiving / clearing it out?</p>

Even if every of your entries only had 1 byte, 2^64 entries would occupy around 18000000 TB on your hard drive, so I guess you shouldn't worry about this.