McKenney: Stupid RCU Tricks: rcutorture Catches an RCU Bug

The whole point of which is to save the same data twice, and thus enable the system to detect that something bad has happened. Of course, what it does after detecting trouble depends on how bad the trouble is, but it is mandatory that it either replays the log to properly update the data, or reverts the log to properly undo the transaction.

It doesn't matter WHAT happens to the disk, so long as there is not a disk failure that randomly scribbles over the disk, Postgres (and pretty much any other database) will provide guarantees that enable you to get back to a clean state, either pre- or post- attempted write.

For example, in the database I want to write I'm planning to use COW. Provided (big if :-( the OS doesn't muck up my user-space write order, that's guaranteed not to corrupt data.

Cheers,
Wol