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Re: SV: Different kind of access methods

From: Larry Jones
Subject: Re: SV: Different kind of access methods
Date: Thu, 14 Dec 2000 11:57:26 -0500 (EST)

Noel L Yap writes:
> I had heard that mkdir under NFS is not an atomic operation.  If this is true,
> then CVS locks won't be atomic either, thereby making it possible for two
> developers to checkin the same things at the same time -- this would be very
> bad.

It depends on how you look at it.  It's probably more accurate to say
that mkdir is atomic but not idempotent; that is, mkdir *on the server*
is an atomic operation -- which means that there is no chance of two
different CVS clients thinking they both own the same lock -- but if the
client repeats the operation (which it will if it doesn't receive the
reply from the server for some reason) it will fail and the client will
think that it doesn't own the lock when it really does.  This leads to
denial of service since you have a lock that will never get deleted, but
it can't cause data corruption.

-Larry Jones

These pictures will remind us of more than we want to remember.
-- Calvin's Mom

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