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From Brian Bockelman <bbock...@cse.unl.edu>
Subject Re: DataBlockScanner scan period
Date Thu, 14 Oct 2010 00:07:30 GMT
Hi Thanh,

The scan period is the period that hadoop *attempts* to complete an entire node scan.  That
is, if it's set to 3 weeks, HDFS will try to scan each block once every 3 weeks.

Obviously, depending on the bandwidth you have made available to the scanning thread, you
can specify impossibly small periods.

Brian

On Oct 13, 2010, at 7:01 PM, Thanh Do wrote:

> Hi again,
> 
> Could any body explain to me about the scanning period
> policy of DataBlockScanner? That is who often it wake up
> and scan a block file.
> When looking at the code, I found
> 
> static final long DEFAULT_SCAN_PERIOD_HOURS = 21*24L; // three weeks
> 
> 
> but definitely it does not wake up and pick a random block
> to verify every three weeks, right?
> 
> Thanks a lot,
> Thanh


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