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Date: Mon, 2 Jul 2012 22:39:32 +0200
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 <CADcMMgFtvy2CZCjUmXkGR3s3zzzEFNBtPi21yNM-QfQk+hsH5A@mail.gmail.com>
Subject: Re: WAL corruption
From: Stack <stack@duboce.net>
To: user@hbase.apache.org
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On Mon, Jul 2, 2012 at 7:37 PM, Bryan Keller <bryanck@gmail.com> wrote:
> During an upgrade of my cluster to 0.90 to 0.92 over the weekend, the WAL=
 (files in the /hbase/.logs directory) was corrupted and it prevented HBase=
 from starting up. The exact exception was "java.io.IOException: Could not =
obtain the last block locations" on the WAL files.
>

Next time, run hdfs fsck and see what it says about your WALs.

> I was able to recover by deleting the /hbase/.logs directory. My question=
 is, if HBase had no pending updates, i.e. nothing writing to it, is there =
any risk of data loss by deleting the WAL directory? For example, does reba=
lancing, flushing, or compaction use the WAL or is the WAL used only for in=
serts/updates/deletes?

Only by inserts, etc.

You could have lost data if edits were in memory on regionserver only
and they had not yet been flushed.

St.Ack