It seems there's an error reporting the Key cache hit rate. The value is
always 0.0 and I have a feeling it's incorrect. This is seen both by using
notetool cfstats as well as accessing JMX directly
(org.apache.cassandra.db:type=Caches,keyspace=outbrain_kvdb,cache=KvAdsKeyCache
RecentHitRate)
What happens if you disable row cache?
On Tue, May 25, 2010 at 4:53 AM, Ran Tavory wrote:
> It seems there's an error reporting the Key cache hit rate. The value is
> always 0.0 and I have a feeling it's incorrect. This is seen both by using
> notetool cfstats as well as accessing JMX directly
>
If I disable row cache the numbers look good - key cache hit rate is > 0, so
it seems to be related to row cache.
Interestingly, after running for a really long time and with both row and
keys caches I do start to see Key cache hit rate > 0 but the numbers are so
small that it doesn't make sense.
It sure sounds like you're seeing the "my row cache contains the
entire hot data set, so the key cache only gets the cold reads"
effect.
On Wed, May 26, 2010 at 2:54 PM, Ran Tavory wrote:
> If I disable row cache the numbers look good - key cache hit rate is > 0, so
> it seems to be related to ro
so the row cache contains both rows and keys and if I have large enough row
cache (in particular if row cache size equals key cache size) then it's just
wasteful to keep another key cache and I should eliminate the key-cache,
correct?
On Thu, May 27, 2010 at 1:21 AM, Jonathan Ellis wrote:
> It s
Essentially, yes.
On Wed, May 26, 2010 at 11:25 PM, Ran Tavory wrote:
> so the row cache contains both rows and keys and if I have large enough row
> cache (in particular if row cache size equals key cache size) then it's just
> wasteful to keep another key cache and I should eliminate the key-ca
