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From Lucas Stanley <lucas23...@gmail.com>
Subject Re: HBase failure scenarios
Date Tue, 11 Jun 2013 00:39:39 GMT
Thanks Azuryy!

So, when a write is successful to the WAL on the responsible region server,
in fact that means that the write was committed to 3 total DataNodes,
correct?


On Mon, Jun 10, 2013 at 5:37 PM, Azuryy Yu <azuryyyu@gmail.com> wrote:

> yes. datanode write is pipeline. and only if pipeline writing finished, dn
> return ok.
>
> --Send from my Sony mobile.
> On Jun 11, 2013 8:27 AM, "Lucas Stanley" <lucas23145@gmail.com> wrote:
>
> > Hi,
> >
> > In the Strata 2013 training lectures, Jonathan Hsieh from Cloudera said
> > something about HBase syncs which I'm trying to understand further.
> >
> > He said that HBase sync guarantees only that a write goes to the local
> disk
> > on the region server responsible for that region and in-memory copies go
> on
> > 2 other machines in the HBase cluster.
> >
> > But I thought that when the write goes to the WAL on the first region
> > server, that the HDFS append would push that write to 3 machines total in
> > the HDFS cluster. In order for the append write to the WAL to be
> > successful, doesn't the DataNode on that machine have to pipeline the
> write
> > to 2 other DataNodes?
> >
> > I'm not sure what Jonathan was referring to when he said that 2 in-memory
> > copies go to other HBase machines? Even when the memstore on the first
> > region server gets full, doesn't the flush to the HFile get written on 3
> > HDFS nodes in total?
> >
>

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