cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Ryan King <r...@twitter.com>
Subject Re: cassandra row cache
Date Thu, 13 Jan 2011 20:24:04 GMT
I'm not sure if this is entirely true, but I *think* older version of
cassandra used a version of the ConcurrentLinkedHashmap (which backs
the row cache) that used the Second Chance algorithm, rather than LRU,
which might explain this non-LRU-like behavior. I may be entirely
wrong about this though.

-ryan

On Thu, Jan 13, 2011 at 11:05 AM, Saket Joshi <sjoshi@touchcommerce.com> wrote:
> Yes it does change.
>
> -----Original Message-----
> From: Jonathan Ellis [mailto:jbellis@gmail.com]
> Sent: Thursday, January 13, 2011 11:01 AM
> To: user
> Subject: Re: cassandra row cache
>
> does the cache size change between 2nd and 3rd time?
>
> On Thu, Jan 13, 2011 at 10:47 AM, Saket Joshi <sjoshi@touchcommerce.com>
> wrote:
>> Hi,
>>
>> I am running a 15 node cluster ,version 0.6.8, Linux 64bit OS, using
> mmap
>> I/O, 6GB ram allocated. I have row cache enabled to 80000 keys (mean
> row
>> size is 2KB). I am observing a strange behaviour.. I query for 1.6
> Million
>> rows across the cluster and time taken is around 40 mins , I query the
> same
>> data again , the time now is 25 mins to fetch data (i am expecting the
> cache
>> to be warm now) , but i see row cache hit rate around 30% . Now i
> request
>> the same data 3rd time, time to fetch is under 4 mins and cache hit
> ratios
>> are 99% ... Does any one have an idea why this may be happening ?
>>
>>
>>
>>
>>
>> Thanks,
>>
>> Saket
>
>
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of Riptano, the source for professional Cassandra support
> http://riptano.com
>

Mime
View raw message