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From Jay Kreps <jay.kr...@gmail.com>
Subject Re: High CPU usage of Crc32 on Kafka broker
Date Thu, 06 Nov 2014 23:23:45 GMT
I suspect it is possible to save and reuse the CRCs though it might be a
bit of an invasive change. I suspect the first usage is when we are
checking the validity of the messages and the second is from when we
rebuild the compressed message set (I'm assuming you guys are using
compression because I think we optimize this out otherwise). Technically I
think the CRCs stay the same.

An alternative approach, though, would be working to remove the need for
recompression entirely on the broker side by making the offsets in the
compressed message relative to the base offset of the message set. This is
a much more invasive change but potentially better as it would also remove
the recompression done on the broker which is also CPU heavy.

-Jay

On Thu, Nov 6, 2014 at 2:36 PM, Allen Wang <awang@netflix.com.invalid>
wrote:

> Sure. Here is the link to the screen shot of jmc with the JTR file loaded:
>
> http://picpaste.com/fligh-recorder-crc.png
>
>
>
> On Thu, Nov 6, 2014 at 2:12 PM, Neha Narkhede <neha.narkhede@gmail.com>
> wrote:
>
> > Allen,
> >
> > Apache mailing lists don't allow attachments. Could you please link to a
> > pastebin or something?
> >
> > Thanks,
> > Neha
> >
> > On Thu, Nov 6, 2014 at 12:02 PM, Allen Wang <awang@netflix.com.invalid>
> > wrote:
> >
> > > After digging more into the stack trace got from flight recorder (which
> > is
> > > attached), it seems that Kafka (0.8.1.1) can optimize the usage of
> Crc32.
> > > The stack trace shows that Crc32 is invoked twice from Log.append().
> > First
> > > is from the line number 231:
> > >
> > > val appendInfo = analyzeAndValidateMessageSet(messages)
> > >
> > > The second time is from line 252 in the same function:
> > >
> > > validMessages = validMessages.assignOffsets(offset, appendInfo.codec)
> > >
> > > If one of the Crc32 invocation can be eliminated, we are looking at
> > saving
> > > at least 7% of CPU usage.
> > >
> > > Thanks,
> > > Allen
> > >
> > >
> > >
> > >
> > > On Wed, Nov 5, 2014 at 6:32 PM, Allen Wang <awang@netflix.com> wrote:
> > >
> > >> Hi,
> > >>
> > >> Using flight recorder, we have observed high CPU usage of CRC32
> > >> (kafka.utils.Crc32.update()) on Kafka broker. It uses as much as 25%
> of
> > CPU
> > >> on an instance. Tracking down stack trace, this method is invoked by
> > >> ReplicaFetcherThread.
> > >>
> > >> Is there any tuning we can do to reduce this?
> > >>
> > >> Also on the topic of CPU utilization, we observed that overall CPU
> > >> utilization is proportional to AllTopicsBytesInPerSec metric. Does
> this
> > >> metric include incoming replication traffic?
> > >>
> > >> Thanks,
> > >> Allen
> > >>
> > >>
> > >
> >
>

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