On Tue, May 28, 2013 at 7:09 AM, jingguo yao <[email protected]> wrote:
> Section 2.1.3 says that Hadoop 1.0.4 works with HBase-0.94.x [1]. And > Section 2.1.3.3 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. Yours, St.Ack
