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From Dan Kinder <dkin...@turnitin.com>
Subject Re: compression cpu overhead
Date Wed, 04 Nov 2015 18:07:01 GMT
To clarify, writes have no *immediate* cpu cost from adding the write to
the memtable, however the compression overhead cost is paid when writing
out a new SSTable (whether from flushing a memtable or compacting), correct?

So it sounds like when reads >> writes then Tushar's comments are accurate,
but for a high write workload flushing and compactions would create most of
the overhead.

On Tue, Nov 3, 2015 at 6:03 PM, Jon Haddad <jonathan.haddad@gmail.com>
wrote:

> You won't see any overhead on writes because you don't actually write to
> sstables when performing a write.  Just the commit log & memtable.
> Memtables are flushes asynchronously.
>
> On Nov 4, 2015, at 1:57 AM, Tushar Agrawal <agrawal.tushar@gmail.com>
> wrote:
>
> For writes it's negligible. For reads it makes a significant difference
> for high tps and low latency workload. You would see up to 3x higher cpu
> with LZ4 vs no compression. It would be different for different h/w
> configurations.
>
>
> Thanks,
> Tushar
> (Sent from iPhone)
>
> On Nov 3, 2015, at 5:51 PM, Dan Kinder <dkinder@turnitin.com> wrote:
>
> Most concerned about write since that's where most of the cost is, but
> perf numbers for a any workload mix would be helpful.
>
> On Tue, Nov 3, 2015 at 3:48 PM, Graham Sanderson <graham@vast.com> wrote:
>
>> On read or write?
>>
>> https://issues.apache.org/jira/browse/CASSANDRA-7039 and friends in 2.2
>> should make some difference, I didn’t immediately find perf numbers though.
>>
>> On Nov 3, 2015, at 5:42 PM, Dan Kinder <dkinder@turnitin.com> wrote:
>>
>> Hey all,
>>
>> Just wondering if anyone has done seen or done any benchmarking for the
>> actual CPU overhead added by various compression algorithms in Cassandra
>> (at least LZ4) vs no compression. Clearly this is going to be workload
>> dependent but even a rough gauge would be helpful (ex. "Turning on LZ4
>> compression increases my CPU load by ~2x")
>>
>> -dan
>>
>>
>>
>
>
> --
> Dan Kinder
> Senior Software Engineer
> Turnitin – www.turnitin.com
> dkinder@turnitin.com
>
>
>


-- 
Dan Kinder
Senior Software Engineer
Turnitin – www.turnitin.com
dkinder@turnitin.com

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