Regards, Dhaval ________________________________ From: Upendra Yadav <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] 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
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 <[EMAIL PROTECTED]> To: [EMAIL PROTECTED]; Dhaval Shah <[EMAIL PROTECTED]> Sent: Tuesday, 25 February 2014 1:18 PM Subject: Re: Need some information over WAL
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 <[EMAIL PROTECTED]>wrote:
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 <[EMAIL PROTECTED]>wrote:
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