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From Lucas Stanley <lucas23...@gmail.com>
Subject HBase failure scenarios
Date Tue, 11 Jun 2013 00:26:39 GMT

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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