cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Wayne <>
Subject Key Caching
Date Mon, 26 Jul 2010 16:47:55 GMT
I am trying to use the key cache, and I had some basic questions as to how
it works. There seem to be settings based on % and total count, but not on
total cache size like most caching mechanisms. Is the cache stored in the
jvm heap or somewhere else? We have 24gb RAM nodes with a 8gb jvm heap size.
Is the key cache sharing the 8gb heap or is it separate? Can we end up
pushing out to swap if the key cache gets too big (if not in jvm)? We would
prefer to set the jvm heap to 8gb and key cache to 8-10 gb, and then do some
testing with cache hit rates to determine how many nodes we need to keep
most keys in cache. High key cache hit rates are vital to good read
performance, and we need some help to figure out the best way to
optimize/design our cluster.

What is the the key cache capacity in cfstats? How is this calculated? I
also see the stats get reset often and cache is cleared quite often, what
triggers the flushing of key cache? Is it compaction? Given that our keys do
not change too much we would prefer them to stay within cache as long as
possible. We have a very wide data model so having all keys in cache is a
realistic possibility for us, we just need some help figuring out how to
design our cluster for this. We are currently testing with 4 nodes with
replication factor of 3 (24gb ram 8 core), and we plan to expand the node
count as required to fit most/all keys into memory.

Thanks in advance for any help you can provide.


View raw message