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>: > > We still ship with vfs.timestamp_precision=0 by default meaning that VFS > timestamps have a granularity of one second. It is not unusual on modern > systems for multiple updates to a file or directory to occur within a single > second (and thus share the same effective timestamp). This can break things > that depend on timestamps to know when something has changed or is stale (such > 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)? Erikhelp
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