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Date: Tue, 12 Jul 2011 16:53:42 +0200
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 <CAO5xsd361JqZcXbm2+n+dqiNERfvFh7ygJgVYuaQW_=f27NgGA@mail.gmail.com>
Subject: Re: Meaning of 'nodetool repair has to run within GCGraceSeconds'
From: Peter Schuller <peter.schuller@infidyne.com>
To: user@cassandra.apache.org
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> From "Cassandra the definitive guide" - Basic Maintenance - Repair
> "Running nodetool repair causes Cassandra to execute a major compaction..=
...
> During a major compaction (see =E2=80=9CCompaction=E2=80=9D in the Glossa=
ry), the
> server initiates a
> TreeRequest/TreeReponse conversation to exchange Merkle trees with neighb=
oring
> nodes."
>
> So is this text from the book misleading ?

It's just being a bit less specific (I suppose maybe misleading can be
claimed). If you repair everything on a node, that will imply a
validating compaction (i.e., do the read part of the compaction stage
but don't merge to and write new sstables) which is expensive for the
usual reasons with disk I/O; it's "major" since it covers all data.
The data read is in fact used to calculate a merkle tree for
comparison with neighbors, as claimed.

--=20
/ Peter Schuller