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From Vladimir Rodionov <vladrodio...@gmail.com>
Subject Re: HBase reads, isolation levels and RegionScanner internal locking
Date Fri, 12 Sep 2014 16:53:18 GMT
Michael, this is HBase developers mailing list.

-Vladimir




On Fri, Sep 12, 2014 at 12:08 AM, Michael Segel <michael_segel@hotmail.com>
wrote:

> Silly question…
>
> HBase uses the term RLL (row level locking) to make the writes to a row
> atomic.
>
> When you start to get in to isolation, RLL takes on a different meaning.
>
> So now you have to better define what do you mean by locking. Are you
> taking about HBase RLL,
> or are you talking about Transactional RLL ( RDBMS RLL) ?
>
>
> On Sep 11, 2014, at 11:58 PM, Vladimir Rodionov <vladrodionov@gmail.com>
> wrote:
>
> > Hi, all
> >
> > We have two isolation levels in (used to be in Scan) in Query now. See:
> > https://issues.apache.org/jira/browse/HBASE-11936
> >
> > I moved isolation levels API from Scan upward to Query class. The reason:
> > this API was not available for Get operations. The rationals? Improve
> > performance of get and multi-gets over the same region.
> >
> > As many of you aware, RegionScannerImpl is heavily synchronized on
> internal
> > region's lock.  Now some questions:
> >
> > 1. Is it safe to bypass this locking (in next() call) in READ_UNCOMMITTED
> > mode?
> > We will do all necessary checks, of course, before calling nextRaw().
> > 2. What was the reason of this locking in a first place for reads in
> > READ_COMMITTED mode? Except obvious - no-dirty-reads allowed? Can someone
> > tell me what else bad can happen?
> >
> > -Vladimir
>
>

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