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From Aniket Bhatnagar <aniket.bhatna...@gmail.com>
Subject Re: Is 30 a too high partition number?
Date Tue, 08 Oct 2013 14:29:30 GMT
Thanks Neha. Is it worthwhile to investigate an option to store topic
metadata (partitions, etc) into another consistent data store (MySQL,
HBase, etc)? Should we make this feature pluggable?

The reason I am thinking we may need to go surpass the 2000 total partition
limit is because there may be genuine use cases to have high number of
topics. For example, in my particular case, I am using Kafka as a buffer to
store data arriving from various sensors deployed in physical world. These
sensors may be short lived or may be long lived. I was thinking of having
individual topics for each sensor. This ways, if a badly behaving sensor
attempts to pushes the data at a much faster rate than we can process as a
Kafka consumer, we will eventually overflow and start losing data for that
particular sensor. However, we can still potentially continue to process
data from other sensors that are pushing data at manageable rate. If I go
with 1 topic for all the sensors, 1 misbehaving sensor can potentially lead
us not catching up with the topic in the retention period thus making us
loose data from all sensors.

The other issue is that if we go with a topic per sensor and the sensors
are short lived and we have reached a threshold of 2000 sensors already
deployed, Kafka will stop working (because of Zookeeper limitation) if
though the previously deployed sensors may not be active at all.

I am sure there may be other genuine use cases for having topics much
larger than 2000.

On 4 October 2013 19:04, Neha Narkhede <neha.narkhede@gmail.com> wrote:

> You probably want to think of this in terms of number of partitions on a
> single broker, instead of per topic since I/O is the limiting factor in
> this case. Another factor to consider is total number of partitions in the
> cluster as Zookeeper becomes a limiting factor there. 30 partitions is not
> too large provided the total number of partitions doesn't exceed roughly
> couple thousand. To give you an example, some of our clusters are 16 nodes
> big and some of the topics on those clusters have 30 partitions.
> Thanks,
> Neha
> On Oct 4, 2013 4:15 AM, "Aniket Bhatnagar" <aniket.bhatnagar@gmail.com>
> wrote:
> > I am using kafka as a buffer for data streaming in from various sources.
> > Since its a time series data, I generate the key to the message by
> > combining source ID and minute in the timestamp. This means I can utmost
> > have 60 partitions per topic (as each source has its own topic). I have
> > set num.partitions to be 30 (60/2) for each topic in broker config. I
> don't
> > have a very good reason to pick 30 as default number of partitions per
> > topic but I wanted it to be a high number so that I can achieve high
> > parallelism during in-stream processing. I am worried that having a high
> > number  like 30 (default configuration had it as 2), it can negatively
> > impact kafka performance in terms of message throughput or memory
> > consumption. I understand that this can lead to many files per partition
> > but I am thinking of dealing with it by having multiple directories on
> the
> > same disk if at all I run into issues.
> >
> > My question to the community is that am I prematurely attempting to
> > optimizing the partition number as right now even a partition number of 5
> > seems sufficient and hence will run into unwanted issues? Or is 30 an Ok
> > number to use for number of partitions?
> >

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