[anarazel]

> - allows a separate high-performance device to be used for the log. This is important because the cost of journalling can be high when lots of fsyncs are being used to ensure integrity (i.e. try running a write performance test on a database like postgresql using ext4 with and without journalling, you'll see a difference).

In a proper setup (mount options journal=writeback,noatime,relatime, wal configured reasonably wrt max_wal_size/checkpoint_segments) the overhead due to ext4 journaling shouldn't be a major factor. You'll see some overhead initially when the WAL segments are allocated as you go, but after that they'll be recycled.

For OLTP write heavy databases I'd say the intent log is more a liability than an advantage, it's easy to screw over performance and/or storage lifetime with it.