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Subject: Re: Change default VFS timestamp precision?
From: Erik Cederstrand <erik@cederstrand.dk>
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Date: Wed, 17 Dec 2014 10:04:08 +0100
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To: John Baldwin <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=