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From: Sandy Pratt <prattrs@adobe.com>
To: "user@hbase.apache.org" <user@hbase.apache.org>
Date: Mon, 19 Mar 2012 12:46:59 -0700
Subject: RE: Hbase Transactional support
Thread-Topic: Hbase Transactional support
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Maysam,

I wasn't aware of Omid before this post, so thanks for sharing that.  I rea=
lly like the approach and indeed our own implementation of transactions on =
HBase uses MVCC and optimistic concurrency control with a centralized trans=
action manager.  I think it's a great fit for HBase.

One question though.  You mention detection of write-write conflicts, but n=
ot write-read conflicts.   I'm guessing that this is because you're shootin=
g for non-serializable snapshot isolation.  Why not detect write-read anoma=
lies and get to serializable isolation (or at least closer to it)?  For exa=
mple it seems like you could detect the write skew anomaly (described here =
http://en.wikipedia.org/wiki/Snapshot_isolation) by tracking a little more =
state in your Status Oracle.  Were you trying to reduce state or decentrali=
ze it or something?  Is there simply no need for that level of isolation?

Apologies if this is clear in the code, which I haven't yet read thoroughly=
.

Thanks,
Sandy


> -----Original Message-----
> From: Maysam Yabandeh [mailto:maysam@yahoo-inc.com]
> Sent: Monday, March 19, 2012 11:45
> To: user@hbase.apache.org
> Subject: Re: Hbase Transactional support
>=20
> Hi Deepika,
>=20
> Omid provides Snapshot Isolation (SI), which is a well-known isolation
> guarantee in database systems such as Oracle. In short, each transaction
> reads from a consistent snapshot that does not include partial changes by
> concurrent (or failed) transactions. SI also prevents write-write conflic=
ts
> between concurrent transactions. The overhead of Omid on HBase is
> negligible and does not require any changes into HBase, with the only
> exception of HBase garbage collection algorithm that is replaced via a
> coprocessor. hbase-trx, on the other hand, does not provide read snapshot=
s
> and is not safe with client failures. You can find a more detailed compar=
ison in
> the Omid wiki page:
> https://github.com/yahoo/omid/wiki
>=20
> Cheers
> - Maysam Yabandeh
>=20
> On Mar 19, 2012, at 6:49 PM, Deepika Khera wrote:
>=20
> > Hi,
> >
> > I have some map reduce jobs that write to Hbase. I am trying to pick a
> > library that could provide transactional support for Hbase. I looked
> > at Omid and hbase-trx .
> >
> > Could you please provide me with a comparison between the two so I can
> > make the right choice.
> > Are there any other ways to do this?
> >
> > Thanks,
> > Deepika
> >
> >
> >
> >