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From: Sandy Pratt <prattrs@adobe.com>
To: "'zookeeper-user@hadoop.apache.org'" <zookeeper-user@hadoop.apache.org>
Date: Tue, 19 Oct 2010 11:33:05 -0700
Subject: zxid integer overflow
Thread-Topic: zxid integer overflow
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Just as a thought experiment, I was pondering the following:

ZK stamps each change to its managed state with a zxid (http://hadoop.apach=
e.org/zookeeper/docs/r3.2.1/zookeeperInternals.html).  That ID consists of =
a 64 bit number in which the upper 32 bits are the epoch, which changes whe=
n the leader does, and the bottom 32 bits are a counter, which is increment=
ed by the leader with every change.  If 1000 changes are made to ZK state e=
ach second (which is 1/20th of the peak rate advertised), then the counter =
portion will roll over in 2^32 / (86400 * 1000) =3D 49 days.

Now, assuming that my math is correct, is this an actual concern?  For exam=
ple, if I'm using ZK to provide locking for a key value store that handles =
transactions at about that rate, am I setting myself up for failure?

Thanks,

Sandy

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