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From Nicolas Spiegelberg <nspiegelb...@facebook.com>
Subject Hlog Group Commit Question: SequenceFileLogReader
Date Tue, 26 Jan 2010 20:35:17 GMT
Hi,

I am trying to backport the HLog group commit functionality to Hbase 0.20.  For proper reliability,
I am working with Dhruba to get the 0.21 syncFs() changes from HDFS ported back to HDFS 0.20
as well.  When going through a peer review of the modified code, my group had a question about
the SequenceFileLogReader.java (WALReader).  I am hoping that you guys could be of assistance.

I know that there is an open issue [HBASE-2069] where Hlog::splitLog() does not call DFSDataInputStream::getVisibleLength(),
which would properly sync hflushed, but unclosed, file lengths.  I believe the current workaround
is to open an HDFS file in append mode & then close, which would cause the namenode to
get updates from the datanodes.  However, I don’t see that shim present in Hlog::splitLog()
on the 0.21 trunk.  Is this a pending issue to fix or is calling FSDataInputStream::available()
within WALReaderFsDataInputStream::getPos() sufficient to force the namenode to sync up with
the datanodes?

Nicolas Spiegelberg

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