ah, I missed the part about "key" cache .. I read "row" cache. thx
On 2/16/12 6:14 PM, "Jonathan Ellis" <jbel...@gmail.com> wrote: >Look for this code in SSTableReader.getPosition: > > Pair<Descriptor, DecoratedKey> unifiedKey = new >Pair<Descriptor, DecoratedKey>(descriptor, decoratedKey); > Long cachedPosition = getCachedPosition(unifiedKey, true); > >On Thu, Feb 16, 2012 at 4:23 PM, Todd Burruss <bburr...@expedia.com> >wrote: >> 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 >> > > > >-- >Jonathan Ellis >Project Chair, Apache Cassandra >co-founder of DataStax, the source for professional Cassandra support >http://www.datastax.com
