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Date: Mon, 25 Jun 2012 17:50:06 -0700
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Subject: key_cache_size_in_mb
From: Gurpreet Singh <gurpreet.singh@gmail.com>
To: user@cassandra.apache.org
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Hi,
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?
Thanks
Gurpreet

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<div>Hi,</div><div>I have a question about cassandra 1.1</div><div><br></di=
v><div>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?</div><div=
>
<br></div><div>My observations:</div><div>With key cache disabled, I starte=
d cassandra. I invoked Full GC through jconsole a couple of times just to m=
ake sure that memory is freed up.=A0</div><div>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.</div>
<div><br></div><div>I enabled key cache again by making key_cache_size_in_m=
b 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 th=
e heap size increased to 4.2 gigs. I checked the cache sizing in jconsole.<=
/div>
<div>=A0</div><div>KeyCacheCapacityInMb: 799</div><div>KeyCacheSize: 410,31=
6,048</div><div><br></div><div>This says that the key cache size is 410 mb.=
 However the increase in the heap is 2 gigs. Doesnt add up!!</div><div><br>
</div><div>Can anyone explain this?</div><div>Thanks</div><div>Gurpreet</di=
v>

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