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Subject: What is a reasonable minimum lease time?
Reply-To: ffilz@redhat.com
References: <043701d4925f$7b244530$716ccf90$@mindspring.com>
To:     linux-nfs@vger.kernel.org
From:   Frank Filz <ffilz@redhat.com>
Organization: Red Hat
Message-ID: <378995dd-00b2-a2e8-fbee-025d4fc2eb24@redhat.com>
Date:   Wed, 12 Dec 2018 13:14:59 -0800
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We have an issue with the Ganesha server with very short (2 second) 
lease times. Ganesha uses a 1 second granularity for lease management, 
and considers a time since last renewed equal to the lease time as too 
long. The result is that the lease period may be short close to 2 
seconds depending on when within a given second things actually happened 
(so a last renew at 0.99 with a subsequent renew at 2.01 which is just 
over one second looks like 2 seconds to Ganesha and thus is >= the 2 
second lease time and not good enough. A simple change would be to 
change the >= to a >, which gives one more second, but it still could 
result in the lease time being almost 1 second too short which is 
significant with a 2 second lease time. But if the minimum reasonable 
lease time is more like 5 or 10 seconds, that 1 second becomes less 
significant.

The bigger fix would be to use a finer grained time, but that adds 
complexity, but if people really want to run with 2 second lease times 
and it makes any kind of sense, we would need to make that change.

Thanks


Frank