Correct.

Why are you concerned with the raw throughput, are you accumulating pending
compactions? Are you seeing high sstables per read statistics?

all the best,

Sebastián
On Jan 15, 2016 6:18 PM, "Kai Wang" <dep...@gmail.com> wrote:

> Jeff & Sebastian,
>
> Thanks for the reply. There are 12 cores but in my case C* only uses one
> core most of the time. *nodetool compactionstats* shows there's only one
> compactor running. I can see C* process only uses one core. So I guess I
> should've asked the question more clearly:
>
> 1. Is ~25 M/s a reasonable compaction throughput for one core?
> 2. Is there any configuration that affects single core compaction
> throughput?
> 3. Is concurrent_compactors the only option to parallelize compaction? If
> so, I guess it's the compaction strategy itself that decides when to
> parallelize and when to block on one core. Then there's not much we can do
> here.
>
> Thanks.
>
> On Fri, Jan 15, 2016 at 5:23 PM, Jeff Jirsa <jeff.ji...@crowdstrike.com>
> wrote:
>
>> With SSDs, the typical recommendation is up to 0.8-1 compactor per core
>> (depending on other load).  How many CPU cores do you have?
>>
>>
>> From: Kai Wang
>> Reply-To: "user@cassandra.apache.org"
>> Date: Friday, January 15, 2016 at 12:53 PM
>> To: "user@cassandra.apache.org"
>> Subject: compaction throughput
>>
>> Hi,
>>
>> I am trying to figure out the bottleneck of compaction on my node. The
>> node is CentOS 7 and has SSDs installed. The table is configured to use
>> LCS. Here is my compaction related configs in cassandra.yaml:
>>
>> compaction_throughput_mb_per_sec: 160
>> concurrent_compactors: 4
>>
>> I insert about 10G of data and start observing compaction.
>>
>> *nodetool compaction* shows most of time there is one compaction.
>> Sometimes there are 3-4 (I suppose this is controlled by
>> concurrent_compactors). During the compaction, I see one CPU core is 100%.
>> At that point, disk IO is about 20-25 M/s write which is much lower than
>> the disk is capable of. Even when there are 4 compactions running, I see
>> CPU go to +400% but disk IO is still at 20-25M/s write. I use *nodetool
>> setcompactionthroughput 0* to disable the compaction throttle but don't
>> see any difference.
>>
>> Does this mean compaction is CPU bound? If so 20M/s is kinda low. Is
>> there anyway to improve the throughput?
>>
>> Thanks.
>>
>
>

Reply via email to