[poofyleek]

It is complex and interesting. I am a novice database user. But I do know many databases use 'gettimeofday' quite a lot. Just strace any SELECT query. Most databases I have used, including Postgresql, also have to implement MVCC which mostly depend on timestamps. Imagine the hypervisor CPU and memory pressure induced time drift, or even drift in distributed cluster of database nodes. It hurts my head to think of the cases that will give me the wrong values or wrong estimate for getting the values. It is an interesting area.

[pgaddict]

MVCC has nothing to do with timestamps, particularly not with timestamps generated from gettimeofday(), but with XIDs which you might imagine as a monotonous sequence of integers, assigned at the start of a transaction. You might call that a timestamp, but the trouble is that what matters is commit order, and the XID has nothing to do with that. Which is why the MVCC requires 'snapshots' - a list of transactions that are in progress.