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From Eran Chinthaka Withana <eran.chinth...@gmail.com>
Subject Re: Key cache hit rate issue
Date Thu, 16 Feb 2012 19:48:03 GMT
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 <aaron@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 <aaron@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
>>
>>
>>
>
>

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