jonathan, you said the key to the cache is key + sstable? looking at the code it looks like a DecoratedKey is the "row key". how does sstable come into play?
On 2/16/12 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
