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From Stack <st...@duboce.net>
Subject Re: Does Hadoop 1.0.4 provide a durable sync for HBase-0.94.6?
Date Tue, 28 May 2013 16:53:19 GMT
On Tue, May 28, 2013 at 7:09 AM, jingguo yao <yaojingguo@gmail.com> wrote:

> Section 2.1.3 says that Hadoop 1.0.4 works with HBase-0.94.x [1]. And
> Section says that 1.0.4 has a working durable sync. But when I
> check the source code of DFSClient.DFSOutputStream's sync method, I
> finds the following javadoc:
>     /**
>      * All data is written out to datanodes. It is not guaranteed
>      * that data has been flushed to persistent store on the
>      * datanode. Block allocations are persisted on namenode.
>      */
> So it seems that sync does not support a durable sync. It contradicts
> with [1].
> Can anybody help me on this confusion? Thanks.

This issue is probably the best source for the state of sync in hbase (and
hdfs): https://issues.apache.org/jira/browse/HBASE-5954

In short, the refguide is misleading -- let me fix -- as 1.0.4 indeed has a
sync but it is just a sync to the memory of three datanodes, not a true
fsync out to disk.  The above cited issue is tracking issues that our Lars
and other have contributed to HDFS to add fsync support.


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