Mailing-List: contact user-help@hbase.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@hbase.apache.org
Received-SPF: neutral (athena.apache.org: local policy)
Message-ID: <946329.68110.qm@web65512.mail.ac4.yahoo.com>
Date: Sun, 17 Apr 2011 12:46:52 -0700 (PDT)
From: Andrew Purtell <apurtell@apache.org>
Reply-To: apurtell@apache.org
Subject: Re: Region Splitting for moderate amount of daily data - Improve
 MapReduce Performance
To: user@hbase.apache.org
In-Reply-To: <BANLkTimtYcP9DEeNAz7fZvp5SKUYP=LxAg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii

Jason,

> Andrew, when you say this:
> 
> > Because HBase is a DOT it can provide strongly consistent
> > and atomic operations on rows, because rows exist in only
> > one place at a time.
> 
> This excludes the use of HBase replication?

Yes.

With the new replication feature of 0.92 edits are streamed from one cluster to another. Row mutations will be consistent/atomic as they are applied at the target, but of course the replication stream may lag for a number of reasons. Therefore the row data according to the view of each cluster may be different. 

> I'm curious as to where HBase replication places the duplicate(?)
> region blocks in HDFS?

The edits are streamed from the WAL. WALs are rolled per usual but are kept perhaps for a longer period of time; until all of their replication scoped edits have been streamed to the target cluster.  

> Also currently is there pass the baton failover when a replicated
> region master fails?

Yes. Via mechanisms mediated by ZooKeeper. But J-D could say more here. 

   - Andy