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From aaron morton <aa...@thelastpickle.com>
Subject Re: performance is drastically degraded after 0.7.8 --> 1.0.11 upgrade
Date Thu, 30 Aug 2012 05:18:57 GMT
> in terms of our high-rate write load cassandra1.0.11 is about 3 (three!!) times slower
than cassandra-0.7.8
We've not had any reports of a performance drop off. All tests so far have show improvements
in both read and write performance. 

> I agree, such digests save some network IO, but they seem to be very bad in terms of
CPU and disk IO.
The sha1 is created so we can diagnose corruptions in the -Data component of the SSTables.
They are not used to save network IO.
It is calculated while streaming the Memtable to disk so has no impact on disk IO. While not
the fasted algorithm I would assume it's CPU overhead in this case is minimal.

>  there's already relatively small Bloom filter file, which can be used for saving network
traffic instead of sha1 digest.
Bloom filters are used to test if a row key may exist in an SSTable.

> any explanation ?

If you can provide some more information on your use case we may be able to help. 

Cheers


-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 30/08/2012, at 5:18 AM, Илья Шипицин <chipitsine@gmail.com> wrote:

> in terms of our high-rate write load cassandra1.0.11 is about 3 (three!!) times slower
than cassandra-0.7.8
> after some investigation carried out I noticed files with "sha1" extension (which are
missing for Cassandra-0.7.8)
> 
> in maybeWriteDigest() function I see no option fot switching sha1 digests off.
> 
> I agree, such digests save some network IO, but they seem to be very bad in terms of
CPU and disk IO.
> why to use one more digest (which have to be calculated), there's already relatively
small Bloom filter file, which can be used for saving network traffic instead of sha1 digest.
> 
> any explanation ?
> 
> Ilya Shipitsin


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