[Thaxll]

Not it was not the case and there was several serious issues with fsync and PG in the past: https://www.percona.com/blog/2019/02/22/postgresql-fsync-fai...

On MySQL: https://dev.mysql.com/doc/refman/8.0/en/innodb-dedicated-ser...

InnoDB uses O_DIRECT during flushing I/O, but skips the fsync() system call after each write operation.

The fsync thing is more complex than it looks like.

[dijit]

That bug was unfortunate, but you can't say that "it doesn't fsync" because, pedantically, it does, it just ignores the return value.

And, obviously that's a bug, it's designed to do so.

Also, if you write with O_DIRECT, a fsync is not needed, as it's how you tell the OS to block until written.