> On 24 Dec 2020, at 17:15, Michael A. Smith <mich...@smith-li.com> wrote:
>
> With all the buffering that modern disks and filesystems do, a
> specific question has come up a few times with respect to whether or
> not data was actually written after flush. I think it would be pretty
> useful for the standard library to have a variant in the io module
> that would explicitly fsync on close.
>
> You might be tempted to argue that this can be done very easily in
> Python already, so why include it in the standard io module?
>
> 1. It seems to me that it would be better to do this in C, so for the
> folks who need to make a consistency > performance kind of choice,
> they don't have to sacrifice any additional performance.
> 2. Having it in the io library will call attention to this issue,
> which I think is something a lot of folks don't consider. Assuming
> that `close` or `flush` are sufficient for consistency has always been
> wrong (at its limits), but it was less likely to be a stumbling block
> in the past, when buffering was less aggressive and less layered and
> the peak size and continuous-ness of data streams was a more niche
> concern.
> 3. There are many ways to do this, and I think several of them could
> be subtly incorrect. In other words, maybe it can't be done very
> easily and correctly after all. Providing "obviously right" ways to do
> things is the baileywick of the standard library, isn't it?
I have used rename to make a new file appear atomically after it is closed
and I have used fsync to ensure records are on disk before a file is closed.
I've not needed fsync on close yet.
What is the use case that needs this?
Without a compelling use case I'm -1 on this.
Barry
>
> Thanks for your consideration and feedback,
> Michael Smith
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