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
