Date: Wed, 17 Dec 2014 10:04:08 +0100 From: Erik Cederstrand <erik@cederstrand.dk> To: John Baldwin <jhb@freebsd.org> Cc: arch@freebsd.org Subject: Re: Change default VFS timestamp precision? Message-ID: <1087E8D0-4B2F-4941-BDCE-3D50264D7FBB@cederstrand.dk> In-Reply-To: <201412161348.41219.jhb@freebsd.org> References: <201412161348.41219.jhb@freebsd.org>
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> Den 16/12/2014 kl. 19.48 skrev John Baldwin <jhb@freebsd.org>: >=20 > We still ship with vfs.timestamp_precision=3D0 by default meaning that = VFS=20 > timestamps have a granularity of one second. It is not unusual on = modern=20 > systems for multiple updates to a file or directory to occur within a = single=20 > second (and thus share the same effective timestamp). This can break = things=20 > that depend on timestamps to know when something has changed or is = stale (such=20 > as make(1) or NFS clients). Mistaking timestamps for uniqueness is really a design error of the = consumer. Changing granularity to milliseconds will diminish the = problem, but also create harder-to-debug problems when multiple updates = do happen in the same millisecond. Is there no other way than timestamps = to find out if a file has changed (apart from md5 which is too = expensive)? Erik=
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