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From Jan Algermissen <>
Subject Throughput and RAM
Date Tue, 10 Sep 2013 09:30:00 GMT
Based on my tuning work with C* over the last days, I guess I reached the following insights.

Maybe someone can confirm whether they make sense:

The more heap I give to Cassandra (up to the GC tipping point of ~8GB) the more writes it
can accumulate in memtables before doing IO.

The more writes are accumulated in memtables, the closer the IO gets towards the maximum possible
IO throughput (because there will be fewer writes of larger sstables).

So in a sense, C* is designed to maximize IO write efficiency by pre-organizing write queries
in memory. The more memory, the better the organization works (caveat GC).

Cassandra takes this eagerness for consuming writes and organizing the writes in memory to
such an extreme, that any given node will rather die than stop consuming writes.

Especially I am looking a confirmation of the last one.

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