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Subject: RE: setrep
Date: Wed, 4 Jun 2008 02:57:22 -0400
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Thread-Topic: setrep
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From: "Haijun Cao" <haijun@kindsight.net>
To: <core-user@hadoop.apache.org>

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Lohit,

Thanks for the explanation. If that's the case, then it is not slower =
than expected. =20

Haijun


-----Original Message-----
From: lohit [mailto:lohit_bv@yahoo.com]
Sent: Wed 6/4/2008 2:11 AM
To: core-user@hadoop.apache.org
Subject: Re: setrep
=20


>It seems that setrep won't force replication change to the specified =
number immediately, it changed really slowly. just wondering if this is =
the expected behavior? what's the rational for this behavior? is there =
way to speed it up?=20

Yes, it wont force replication to be instant. Once you increase the =
replication factor of a file, namenode adds it to neededReplication =
list. Namenode has a thread running which periodically scans this list =
and chooses a set of blocks which are under replicated and request the =
datanodes to replicate them. This interval is configured using =
dfs.replication.interval config variable. Interval =
dfs.replication.interval is in seconds.
The list of neededReplication also maintains a priority policy, where in =
blocks with only one copy would be replicated first.=20

If you do not have lot of underReplicated blocks, this should happen =
pretty fast. Are you seeing very long delays?=20
Thanks,
Lohit


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