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From Ted Yu <yuzhih...@gmail.com>
Subject Re: Need some information over WAL
Date Tue, 25 Feb 2014 18:29:23 GMT
Minor addition:

bq. WAL is a single and common file for all regions on a region server

hbase:meta has its own WAL file.


On Tue, Feb 25, 2014 at 10:22 AM, Dhaval Shah
<prince_mithibai@yahoo.co.in>wrote:

> yes WAL is a single and common file for all regions on a region server.
> Yes to 1.
> Re 2: HBase will roll over WAL files and eventually delete them when they
> are no longer needed.
>
> Regards,
> Dhaval
>
>
> ________________________________
>  From: Upendra Yadav <upendra1024@gmail.com>
> To: user@hbase.apache.org; Dhaval Shah <prince_mithibai@yahoo.co.in>
> Sent: Tuesday, 25 February 2014 1:18 PM
> Subject: Re: Need some information over WAL
>
>
> Thanks Dhawal....
>
> Oh... whatever i assumed with reading documents (partially).... that was
> wrong...
>
> With ur answer... i have another questions...
> WAL is a single and common file for all region of a Region server.
>
> Is this correct:
> 1. So all operation(including data) will go to WAL... operation by
> operation....
>
> 2. Then on HDFS, HBase will have to perform delete operation on some set of
> WAL files always...
>
>
>
>
> On Tue, Feb 25, 2014 at 11:35 PM, 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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