Essentially, yes. On Wed, May 26, 2010 at 11:25 PM, Ran Tavory <ran...@gmail.com> 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-cache, > correct? > > On Thu, May 27, 2010 at 1:21 AM, Jonathan Ellis <jbel...@gmail.com> wrote: >> >> 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 <ran...@gmail.com> wrote: >> > 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. >> > I have capacity for 10M keys and 10M rows, the number of cached keys is >> > ~5M >> > and very similarly the number of cached rows is also ~5M, however the >> > hit >> > rates are very different, 0.7 for rows and 0.006 for keys. I'd expect >> > the >> > keys hit rate to be identical since none of them reached the limit yet. >> > Key cache capacity: 10000000 >> > Key cache size: 5044097 >> > Key cache hit rate: 0.0062089764058896576 >> > Row cache capacity: 10000000 >> > Row cache size: 5057231 >> > Row cache hit rate: 0.7361241352465543 >> > >> > >> > On Tue, May 25, 2010 at 3:43 PM, Jonathan Ellis <jbel...@gmail.com> >> > wrote: >> >> >> >> What happens if you disable row cache? >> >> >> >> On Tue, May 25, 2010 at 4:53 AM, Ran Tavory <ran...@gmail.com> 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 >> >> > >> >> > >> >> > (org.apache.cassandra.db:type=Caches,keyspace=outbrain_kvdb,cache=KvAdsKeyCache >> >> > RecentHitRate) >> >> > <ColumnFamily CompareWith="BytesType" Name="KvAds" >> >> > RowsCached="10000000" >> >> > KeysCached="10000000"/> >> >> > Column Family: KvAds >> >> > SSTable count: 7 >> >> > Space used (live): 1288942061 >> >> > Space used (total): 1559831566 >> >> > Memtable Columns Count: 73698 >> >> > Memtable Data Size: 17121092 >> >> > Memtable Switch Count: 33 >> >> > Read Count: 3614433 >> >> > Read Latency: 0.068 ms. >> >> > Write Count: 3503269 >> >> > Write Latency: 0.024 ms. >> >> > Pending Tasks: 0 >> >> > Key cache capacity: 10000000 >> >> > Key cache size: 619624 >> >> > Key cache hit rate: 0.0 >> >> > Row cache capacity: 10000000 >> >> > Row cache size: 447154 >> >> > Row cache hit rate: 0.8460295730014572 >> >> > Compacted row minimum size: 387 >> >> > Compacted row maximum size: 31430 >> >> > Compacted row mean size: 631 >> >> > The Row cache hit rate looks good, 0.8 but Key cache hit rate always >> >> > seems >> >> > to be 0.0 while the number of unique keys stays about 619624 for >> >> > quite a >> >> > while. >> >> > Is it a real caching problem or just a reporting glitch? >> >> >> >> >> >> >> >> -- >> >> Jonathan Ellis >> >> Project Chair, Apache Cassandra >> >> co-founder of Riptano, the source for professional Cassandra support >> >> http://riptano.com >> > >> > >> >> >> >> -- >> Jonathan Ellis >> Project Chair, Apache Cassandra >> co-founder of Riptano, the source for professional Cassandra support >> http://riptano.com > >
-- Jonathan Ellis Project Chair, Apache Cassandra co-founder of Riptano, the source for professional Cassandra support http://riptano.com
