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From Peter Schuller <>
Subject Re: Meaning of 'nodetool repair has to run within GCGraceSeconds'
Date Tue, 12 Jul 2011 14:53:42 GMT
> From "Cassandra the definitive guide" - Basic Maintenance - Repair
> "Running nodetool repair causes Cassandra to execute a major compaction.....
> During a major compaction (see “Compaction” in the Glossary), the
> server initiates a
> TreeRequest/TreeReponse conversation to exchange Merkle trees with neighboring
> 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.

/ Peter Schuller

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