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From Upendra Yadav <upendra1...@gmail.com>
Subject Re: Need some information over WAL
Date Tue, 25 Feb 2014 18:20:40 GMT
Thanks @Ted Yu...


On Tue, Feb 25, 2014 at 11:41 PM, Ted Yu <yuzhihong@gmail.com> wrote:

> bq. Hbase uses append operation in hdfs to store/log WAL.
>
> Following append operation, hdfs sync operation would be called for
> persistence.
>
> FYI
>
>
> On Tue, Feb 25, 2014 at 10:05 AM, Dhaval Shah
> <prince_mithibai@yahoo.co.in>wrote:
>
> > Inline
> >
> > Regards,
> > Dhaval
> >
> >
> > ________________________________
> >  From: Upendra Yadav <upendra1024@gmail.com>
> > To: user@hbase.apache.org
> > Sent: Tuesday, 25 February 2014 1:00 PM
> > Subject: Need some information over WAL
> >
> >
> > I have also doubt over WAL(write ahead log).
> >
> > In hdfs we can write a new file or we can append to old file.
> >
> > Is that correct :
> > 1. WAL only logs operations not its data... just like disk
> journaling(ext4)
> > - No WAL is a log of all new data, not just the operations
> >
> > 2. In case of Region Server failure... WAL replay will depends on Client
> to
> > get each operation's data that yet not committed/flushed to hdfs.
> > - No client will not generally know of a region server failure. It gets
> > the data from the WAL and replays it. The client may not even exist when
> a
> > region server crashes
> >
> > 3. Hbase uses append operation in hdfs to store/log WAL.
> > - Yes
> >
> > Thanks...
>

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