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From Eric Parusel <ericparu...@gmail.com>
Subject Virtual Nodes, lots of physical nodes and potentially increasing outage count?
Date Wed, 05 Dec 2012 16:45:27 GMT
Hi all,

I've been wondering about virtual nodes and how cluster uptime might change
as cluster size increases.

I understand clusters will benefit from increased reliability due to faster
rebuild time, but does that hold true for large clusters?

It seems that since (and correct me if I'm wrong here) every physical node
will likely share some small amount of data with every other node, that as
the count of physical nodes in a Cassandra cluster increases (let's say
into the triple digits) that the probability of at least one failure to
Quorum read/write occurring in a given time period would *increase*.

Would this hold true, at least until physical nodes becomes greater than
num_tokens per node?

I understand that the window of failure for affected ranges would probably
be small but we do Quorum reads of many keys, so we'd likely hit every
virtual range with our queries, even if num_tokens was 256.

Thanks,
Eric

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