In Chapter 2, Database Hardware, the overhead of waiting for physical disk commits was stressed as a likely bottleneck for committing transactions. If you don't have a battery-backed write cache to accelerate that, but you need better commit speed, what can you do? The standard approach is to disable synchronous_commit, which is sometimes alternately referred to as enabling asynchronous commits.
This groups commits into chunks at a frequency determined by the related wal_writer_delay parameter. The default settings guarantee a real commit to disk at most 600 milliseconds after the client commit. During that window, which you can reduce in size with a corresponding decrease in speed-up, that data will not be recovered afterward ...
