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From Franc Carter <franc.car...@sirca.org.au>
Subject Re: keycache persisted to disk ?
Date Mon, 13 Feb 2012 08:46:14 GMT
2012/2/13 R. Verlangen <robin@us2.nl>

> I also noticed that, Cassandra appears to perform better under a continues
> load.
>
> Are you sure the rows you're quering are actually in the cache?
>

I'm making an assumption . . .  I don't yet know enough about cassandra to
prove they are in the cache. I have my keycache set to 2 million, and am
only querying ~900,000 keys. so after the first time I'm assuming they are
in the cache.

cheers


>
>
> 2012/2/13 Franc Carter <franc.carter@sirca.org.au>
>
>> 2012/2/13 R. Verlangen <robin@us2.nl>
>>
>>> This is because of the "warm up" of Cassandra as it starts. On a start
>>> it will start fetching the rows that were cached: this will have to be
>>> loaded from the disk, as there is nothing in the cache yet. You can read
>>> more about this at
>>> http://wiki.apache.org/cassandra/LargeDataSetConsiderations
>>
>>
>> I actually has the opposite 'problem'. I have a pair of servers that have
>> been static since mid last week, but have seen performance vary
>> significantly (x10) for exactly the same query. I hypothesised it was
>> various caches so I shut down Cassandra, flushed the O/S buffer cache and
>> then bought it back up. The performance wasn't significantly different to
>> the pre-flush performance
>>
>> cheers
>>
>>
>>>
>>>
>>> 2012/2/13 Franc Carter <franc.carter@sirca.org.au>
>>>
>>>> On Mon, Feb 13, 2012 at 5:03 PM, zhangcheng <zhangcheng@jike.com>wrote:
>>>>
>>>>> **
>>>>>
>>>>> I think the keycaches and rowcahches are bothe persisted to disk when
>>>>> shutdown, and restored from disk when restart, then improve the performance.
>>>>>
>>>>
>>>> Thanks - that would explain at least some of what I am seeing
>>>>
>>>> cheers
>>>>
>>>>
>>>>>
>>>>> 2012-02-13
>>>>> ------------------------------
>>>>>  zhangcheng
>>>>> ------------------------------
>>>>> *发件人:* Franc Carter
>>>>> *发送时间:* 2012-02-13  13:53:56
>>>>> *收件人:* user
>>>>> *抄送:*
>>>>> *主题:* keycache persisted to disk ?
>>>>>
>>>>> Hi,
>>>>>
>>>>> I am testing Cassandra on Amazon and finding performance can vary
>>>>> fairly wildly. I'm leaning towards it being an artifact of the AWS I/O
>>>>> system but have one other possibility.
>>>>>
>>>>> Are keycaches persisted to disk and restored on a clean shutdown and
>>>>> restart ?
>>>>>
>>>>> cheers
>>>>>
>>>>> --
>>>>>
>>>>> *Franc Carter* | Systems architect | Sirca Ltd
>>>>> <marc.zianideferranti@sirca.org.au>
>>>>>
>>>>> franc.carter@sirca.org.au | www.sirca.org.au
>>>>>
>>>>> Tel: +61 2 9236 9118
>>>>>
>>>>> Level 9, 80 Clarence St, Sydney NSW 2000
>>>>>
>>>>> PO Box H58, Australia Square, Sydney NSW 1215
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> *Franc Carter* | Systems architect | Sirca Ltd
>>>>  <marc.zianideferranti@sirca.org.au>
>>>>
>>>> franc.carter@sirca.org.au | www.sirca.org.au
>>>>
>>>> Tel: +61 2 9236 9118
>>>>
>>>> Level 9, 80 Clarence St, Sydney NSW 2000
>>>>
>>>> PO Box H58, Australia Square, Sydney NSW 1215
>>>>
>>>>
>>>
>>
>>
>> --
>>
>> *Franc Carter* | Systems architect | Sirca Ltd
>>  <marc.zianideferranti@sirca.org.au>
>>
>> franc.carter@sirca.org.au | www.sirca.org.au
>>
>> Tel: +61 2 9236 9118
>>
>> Level 9, 80 Clarence St, Sydney NSW 2000
>>
>> PO Box H58, Australia Square, Sydney NSW 1215
>>
>>
>


-- 

*Franc Carter* | Systems architect | Sirca Ltd
 <marc.zianideferranti@sirca.org.au>

franc.carter@sirca.org.au | www.sirca.org.au

Tel: +61 2 9236 9118

Level 9, 80 Clarence St, Sydney NSW 2000

PO Box H58, Australia Square, Sydney NSW 1215

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