Hi Jonathan, Thanks for the reply. Yes there is a possibility that the keys can be distributed in multiple SSTables, but my data access patterns are such that I always read/write the whole row. So I expect all the data to be in the same SSTable (please correct me if I'm wrong).
For some reason 16637958 (the keys cached) has become a golden number and I don't see key cache increasing beyond that. I also checked memory and I have about 4GB left in JVM memory and didn't see any issues on logs. Thanks, Eran Chinthaka Withana On Thu, Feb 16, 2012 at 1:20 PM, Jonathan Ellis <jbel...@gmail.com> wrote: > So, you have roughly 1/6 of your (physical) row keys cached and about > 1/4 cache hit rate, which doesn't sound unreasonable to me. Remember, > each logical key may be spread across multiple physical sstables -- > each (key, sstable) pair is one entry in the key cache. > > On Thu, Feb 16, 2012 at 1:48 PM, Eran Chinthaka Withana > <eran.chinth...@gmail.com> wrote: > > Hi Aaron, > > > > Here it is. > > > > Keyspace: XXXX > > Read Count: 1123637972 > > Read Latency: 5.757938114343114 ms. > > Write Count: 128201833 > > Write Latency: 0.0682576607387509 ms. > > Pending Tasks: 0 > > Column Family: YY > > SSTable count: 18 > > Space used (live): 103318720685 > > Space used (total): 103318720685 > > Number of Keys (estimate): 92404992 > > Memtable Columns Count: 1425580 > > Memtable Data Size: 359655747 > > Memtable Switch Count: 2522 > > Read Count: 1123637972 > > Read Latency: 14.731 ms. > > Write Count: 128201833 > > Write Latency: NaN ms. > > Pending Tasks: 0 > > Bloom Filter False Postives: 1488 > > Bloom Filter False Ratio: 0.00000 > > Bloom Filter Space Used: 331522920 > > Key cache capacity: 16637958 > > Key cache size: 16637958 > > Key cache hit rate: 0.2708333333333333 > > Row cache: disabled > > Compacted row minimum size: 51 > > Compacted row maximum size: 6866 > > Compacted row mean size: 2560 > > > > Thanks, > > Eran Chinthaka Withana > > > > > > > > On Thu, Feb 16, 2012 at 12:30 AM, aaron morton <aa...@thelastpickle.com> > > wrote: > >> > >> Its in the order of 261 to 8000 and the ratio is 0.00. But i guess 8000 > is > >> bit high. Is there a way to fix/improve it? > >> > >> Sorry I don't understand what you mean. But if the ratio is 0.0 all is > >> good. > >> > >> Could you include the full output from cfstats for the CF you are > looking > >> at ? > >> > >> Cheers > >> > >> ----------------- > >> Aaron Morton > >> Freelance Developer > >> @aaronmorton > >> http://www.thelastpickle.com > >> > >> On 15/02/2012, at 1:00 PM, Eran Chinthaka Withana wrote: > >> > >> Its in the order of 261 to 8000 and the ratio is 0.00. But i guess 8000 > is > >> bit high. Is there a way to fix/improve it? > >> > >> Thanks, > >> Eran Chinthaka Withana > >> > >> > >> On Tue, Feb 14, 2012 at 3:42 PM, aaron morton <aa...@thelastpickle.com> > >> wrote: > >>> > >>> Out of interest what does cfstats say about the bloom filter stats ? A > >>> high false positive could lead to a low key cache hit rate. > >>> > >>> Also, is there a way to warm start the key cache, meaning pre-load the > >>> amount of keys I set as keys_cached? > >>> > >>> See key_cache_save_period when creating the CF. > >>> > >>> Cheers > >>> > >>> > >>> ----------------- > >>> Aaron Morton > >>> Freelance Developer > >>> @aaronmorton > >>> http://www.thelastpickle.com > >>> > >>> On 15/02/2012, at 5:54 AM, Eran Chinthaka Withana wrote: > >>> > >>> Hi, > >>> > >>> I'm using Cassandra 1.0.7 and I've set the keys_cached to about 80% > >>> (using the numerical values). This is visible in cfstats too. But I'm > >>> getting less than 20% (or sometimes even 0%) key cache hit rate. Well, > the > >>> data access pattern is not the issue here as I know they are > retrieving the > >>> same row multiple times. I'm using hector client with dynamic load > balancing > >>> policy with consistency ONE for both reads and writes. Any ideas on > how to > >>> find the issue and fix this? > >>> > >>> Here is what I see on cfstats. > >>> > >>> Key cache capacity: 16637958 > >>> Key cache size: 16637958 > >>> Key cache hit rate: 0.045454545454545456 > >>> > >>> Also, is there a way to warm start the key cache, meaning pre-load the > >>> amount of keys I set as keys_cached? > >>> > >>> Thanks, > >>> Eran > >>> > >>> > >> > >> > > > > > > -- > Jonathan Ellis > Project Chair, Apache Cassandra > co-founder of DataStax, the source for professional Cassandra support > http://www.datastax.com >
