>EXTRA synchronous is like FULL with the addition that the directory containing a rollback journal is synced after that journal is unlinked to commit a transact

>EXTRA synchronous is like FULL with the addition that the directory containing a rollback journal is synced after that journal is unlinked to commit a transaction in DELETE mode. EXTRA provides additional durability if the commit is followed closely by a power loss. It depends on your filesystem whether this is necessary. In any case I'm pretty sure it's not relevant for WAL mode.