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From Gurpreet Singh <>
Subject key_cache_size_in_mb
Date Tue, 26 Jun 2012 00:50:06 GMT
I have a question about cassandra 1.1

Just wanted to confirm if key_cache_size_in_mb is the maximum amount of
memory that key cache will use in memory? If not, what is it?

My observations:
With key cache disabled, I started cassandra. I invoked Full GC through
jconsole a couple of times just to make sure that memory is freed up.
Total heap memory in use is 2.2 gigs. I have almost 550 million keys, so
this looked reasonable as the bloom filter itself is around 1 gig.

I enabled key cache again by making key_cache_size_in_mb to a value 800.
This would lead cassandra to load a previously saved key cache file of size
98 mb on disk. I restarted cassandra again. This time the heap size
increased to 4.2 gigs. I checked the cache sizing in jconsole.

KeyCacheCapacityInMb: 799
KeyCacheSize: 410,316,048

This says that the key cache size is 410 mb. However the increase in the
heap is 2 gigs. Doesnt add up!!

Can anyone explain this?

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