incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "zhangcheng" <zhangch...@jike.com>
Subject Re: Re: Key cache hit rate issue
Date Fri, 17 Feb 2012 02:33:52 GMT
according to the read process, the key of the keycache should be the row key.


2012-02-17 



zhangcheng 



发件人: Todd Burruss 
发送时间: 2012-02-17  06:23:47 
收件人: user@cassandra.apache.org 
抄送: 
主题: Re: Key cache hit rate issue 
 
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" <jbellis@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.chinthaka@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 <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
>>>>
>>>>
>>>
>>>
>>
>
>
>
>-- 
>Jonathan Ellis
>Project Chair, Apache Cassandra
>co-founder of DataStax, the source for professional Cassandra support
>http://www.datastax.com
Mime
View raw message