I probably meant to say "synchronous_commit", which is how data is written to disk from the WAL. If you want full data guarantees, with regular hard drives, you'd be looking at less than 200 transactions per second. You set synchronous_commit to off, and suddenly you can do 10k transactions per second. You can tune when the WAL gets flushed to disk based on time and/or size. So you can set the amount of recent data loss you are comfortable with.

From the docs: "setting this parameter to off does not create any risk of database inconsistency: an operating system or database crash might result in some recent allegedly-committed transactions being lost, but the database state will be just the same as if those transactions had been aborted cleanly. So, turning synchronous_commit off can be a useful alternative when performance is more important than exact certainty"