Hi Anand,
As usual, the answer is that 'it depends' :)
I think that the main question here is: why are you afraid that this setup
would lead to region server hotspotting? Is because you don't know how your
production data will seems?
Based on what you told about your rowkey, you will query mostly by providing
model no. + serial no., but:
1 - How is your rowkey distribution? There are tons of different modelNumbers
AND serialNumbers? Few modelNumbers and a lot of serialNumbers? Few of both?
2 - Putting modelNumber in front of your rowkey means that your data will be
sorted by rowkey. So, what is the rule that determinates a modelNumber
creation? Is it a sequential number that will be increased by time? If so, are
newer members accessed a lot more than older members? If not, what will drive
this number? Is it an encoding rule?
3 - Do you expect more write/read load over a few of these modelNumbers and/or
serialNumbers? Will it be similar to a Pareto Distribution? Distributed over
what?
Also, two other things got my attention here...
1 - Why are you filtering with regex? If your queries are over model no. +
serial no., why don't you just scan starting by your modelNumber+SerialNumber,
and stoping on your next modelNumber+SerialNumber? Or is there another access
pattern that doesn't apply to your composited rowkey?
2 - Why do you have to add a timestamp to ensure uniqueness?
Now, answering your question without more info about your data, you can apply
hash in two ways:
1 - Generating a hash (MD5 is the most common as far as I read about) and using
only this hash as your rowkey. Based on what you have told, this way doesn't
fit your needs, because you would not be able to do apply your filter anymore.
2 - Salting, by prefixing your current rowkey with a pinch of hash. Notice that
the hash portion must be your rowkey prefix to ensure a kind of balanced
distribution over something (where something is your region servers). I'm
working with a case that is a bit similar to yours, and what I'm doing right
now is calculating the hashValue of my rowkey and using a Java Formatter to
create a hex string to prepend to my rowkey. Something like a
String.format("%03x", hashValue)
In both cases, you still have to split your regions in advance, and it will be
better to work your splitting before starting to feed your table with
production data.
Also, you have to study the consequences that changing your rowkey will bring.
It's not for free.
There's a lot of words here and a lot of questions, so by now I feel I started
to shoot in the dark. Try to understand your production data and if you have
more to share, for sure it will help!
Regards,
Cristofer
-----Mensagem original-----
De: AnandaVelMurugan Chandra Mohan [mailto:[email protected]]
Enviada em: segunda-feira, 16 de julho de 2012 02:30
Para: [email protected]
Assunto: Rowkey hashing to avoid hotspotting
Hi,
I am using Hbase to store data about mechanical components. Each component has
model no. and serial no. and some other attributes.
I would be querying my data mostly by model no. and serial no. So I created a
composite key with these two attributes and added timestamp to make it unique.
To filter the data, I use rowkey filter with regex string comparator and it
works well with sample seed data. Now I am afraid whether this set up will lead
to region server hotspotting when we load production data in HBase. I read
hashing may solve this problem. Can some one help me in implementing hashing
the row key? Also I would want the row filter to work as I have to display the
number of components in a web page and I use row key filter for implementing
that functionality? Any guidance would be of great help.
--
Regards,
Anand
