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From Demai Ni <nid...@gmail.com>
Subject Re: HBase region assignment by range?
Date Wed, 08 Apr 2015 18:39:40 GMT
hi, Guys,

many thanks for your quick response.

First, Let me share what I am looking at, which may help to clarify the
intention and answer a few of questions. I am working on a POC to bring in
MPP style of OLAP on Hadoop, and looking for whether it is feasible to have
HBase as Datastore. With HBase, I'd like to take advantage of 1) OLTP
capability ; 2) many filters ; 3) in-cluster replica and between-clusters
replication. I am currently using TPCH schema for this POC, and also
consider star-schema. Since it is a POC, I can pretty much define my rules
and set limitations as it fits. :-)

Why doesn't this(presplit) work for you?

 The reason is that presplit won't guarantee the regions stay at the
pre-assigned regionServer. Let's say I have a very large table and a very
small table with different data distribution, even with the same presplit
value. HBase won't ensure the same range of data located on the same
physical node. Unless we have a custom LB mentioned by @Anoop and @esteban.
Is my understanding correct? BTW, I will look into HBASE-10576 to see
whether it fits my needs.

Is your table staic?
>
while I can make it static for POC purpose, but I will use this limitation,
as I'd like the HBase for its OLTP feature. So besides the 'static' HFile,
need HLOGs on the same local node too. But again, I would worry about the
'static' HFile for now

However as you add data to the table, those regions will eventually split.

 while the region can surely split when more data added-on, but can HBase
keep the new regions still on the same regionServer according to the
predefined bounary? I will worry about hotspot-issue late. that is the
beauty of doing POC instead of production. :-)

What you’re suggesting is that as you do a region scan, you’re going to the
> other table and then try to fetch a row if it exists.
>
Yes, something like that. I am currently using the client API: scan() with
start and end key.  Since I know my start and end keys, and with the
local-read feature, the scan should be local-READ. With some
statistics(such as which one is larger table) and  a hash join
operation(which I need to implement), the join will work with not-too-bad
performance. Again, it is POC, so I won't worry about the situation that a
regionServer hosts too much data(hotspot). But surely, a LB should be used
before putting into production if it ever occurs.

either the second table should be part of the first table in the same CF or
> as a separate CF
>
I am not sure whether it will work for a situation of a large table vs a
small table. The data of the small table has to be duplicated in many
places, and a update of the small table can be costly.

Demai


On Wed, Apr 8, 2015 at 10:24 AM, Esteban Gutierrez <esteban@cloudera.com>
wrote:

> +1 Anoop.
>
> Thats pretty much the only way right now if you need a custom balancing.
> This balancer doesn't have to live in the HMaster and can be invoked
> externally (there are caveats of doing that, when a RS die but works ok so
> far). A long term solution for your the problem you are trying to solve is
> HBASE-10576 by tweaking it a little.
>
> cheers,
> esteban.
>
>
>
>
>
> --
> Cloudera, Inc.
>
>
> On Wed, Apr 8, 2015 at 4:41 AM, Michael Segel <michael_segel@hotmail.com>
> wrote:
>
> > Is your table staic?
> >
> > If you know your data and your ranges, you can do it. However as you add
> > data to the table, those regions will eventually split.
> >
> > The other issue that you brought up is that you want to do ‘local’ joins.
> >
> > Simple single word response… don’t.
> >
> > Longer response..
> >
> > You’re suggesting that the tables in question share the row key in
> > common.  Ok… why? Are they part of the same record?
> > How is the data normally being used?
> >
> > Have you looked at column families?
> >
> > The issue is that joins are expensive. What you’re suggesting is that as
> > you do a region scan, you’re going to the other table and then try to
> fetch
> > a row if it exists.
> > So its essentially for each row in the scan, try a get() which will
> almost
> > double the cost of your fetch. Then you have to decide how to do it
> > locally. Are you really going to write a coprocessor for this?  (Hint: If
> > this is a common thing. Then either the second table should be part of
> the
> > first table in the same CF or as a separate CF. You need to rethink your
> > schema.)
> >
> > Does this make sense?
> >
> > > On Apr 7, 2015, at 7:05 PM, Demai Ni <nidmgg@gmail.com> wrote:
> > >
> > > hi, folks,
> > >
> > > I have a question about region assignment and like to clarify some
> > through.
> > >
> > > Let's say I have a table with rowkey as "row00000 ~ row30000" on a 4
> node
> > > hbase cluster, is there a way to keep data partitioned by range on each
> > > node? for example:
> > >
> > > node1:  <=row10000
> > > node2:  row10001~row20000
> > > node3:  row20001~row30000
> > > node4:  >row30000
> > >
> > > And even when one of the node become hotspot, the boundary won't be
> > crossed
> > > unless manually doing a load balancing?
> > >
> > > I looked at presplit: { SPLITS => ['row100','row200','row300'] } , but
> > > don't think it serves this purpose.
> > >
> > > BTW, a bit background. I am thinking to do a local join between two
> > tables
> > > if both have same rowkey, and partitioned by range (or same hash
> > > algorithm). If I can keep the join-key on the same node(aka
> > regionServer),
> > > the join can be handled locally instead of broadcast to all other
> nodes.
> > >
> > > Thanks for your input. A couple pointers to blog/presentation would be
> > > appreciated.
> > >
> > > Demai
> >
> > The opinions expressed here are mine, while they may reflect a cognitive
> > thought, that is purely accidental.
> > Use at your own risk.
> > Michael Segel
> > michael_segel (AT) hotmail.com
> >
> >
> >
> >
> >
> >
>

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