Bug 3.11.x behavioral, open file buffers not flushed til file closed.

[Chris Angelico]

On Mon, 6 Mar 2023 at 12:41, Greg Ewing via Python-list
<python-list at python.org> wrote:
>
> On 6/03/23 1:02 pm, Cameron Simpson wrote:
> > Also, fsync() need not expedite the data getting to disc. It is equally
> > valid that it just blocks your programme _until_ the data have gone to
> > disc.
>
> Or until it *thinks* the data has gone to the disk. Some drives
> do buffering of their own, which may impose additional delays
> before the data actually gets written.
>

Sadly true. Usually with SSDs. Unfortunately, at that point, there's
nothing ANYONE can do about it, since the OS is deceived as much as
anyone else.

But Cameron is completely right in that fsync's primary job is "block
until" rather than "do this sooner". Adding fsync calls might possibly
cause a flush when one otherwise wouldn't have happened, but generally
they'll slow things down in the interests of reliability.

ChrisA