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From Upendra Yadav <upendra1...@gmail.com>
Subject Re: Need some information over WAL
Date Tue, 25 Feb 2014 18:18:16 GMT
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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