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help / color / mirror / Atom feedFrom: Jacob Champion <[email protected]>
To: [email protected] <[email protected]>
To: [email protected] <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: pg_upgrade parallelism
Date: Tue, 23 Nov 2021 18:54:03 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <YZVbtHKYP02AZDIO@ahch-to>
<[email protected]>
On Wed, 2021-11-17 at 14:34 -0600, Justin Pryzby wrote:
> On Wed, Nov 17, 2021 at 02:44:52PM -0500, Jaime Casanova wrote:
> >
> > - why we read()/write() at all? is not a faster way of copying the file?
> > i'm asking that because i don't actually know.
>
> No portable way. Linux has this:
> https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fman7.org%2Flinux%2Fman-pages%2Fman...
>
> But I just read:
>
> > First support for cross-filesystem copies was introduced in Linux
> > 5.3. Older kernels will return -EXDEV when cross-filesystem
> > copies are attempted.
>
> To me that sounds like it may not be worth it, at least not quite yet.
> But it would be good to test.
I think a downside of copy_file_range() is that filesystems might
perform a reflink under us, and to me that seems like something that
needs to be opted into via clone mode.
(https://lwn.net/Articles/846403/ is also good reading on some sharp
edges, though I doubt many of them apply to our use case.)
--Jacob
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