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From Peter Schuller <>
Subject Re: Can you query Cassandra while it's doing major compaction
Date Fri, 03 Feb 2012 07:44:40 GMT
> If every node in the cluster is running major compaction, would it be able to
> answer any read request?  And is it wise to write anything to a cluster
> while it's doing major compaction?

Compaction is something that is supposed to be continuously running in
the background. As noted, it will have a performance impact in that it
(1) generates I/O, (2) leads to cache eviction, and (if you're CPU
bound rather than disk bound) (3) adds CPU load.

But there is no intention that clients should have to care about
compaction; it's to be viewed as a background operation continuously
happening. A good rule of thumb is that an individual node should be
able to handle your traffic when doing compaction; you don't want to
be in the position where you're just barely dealing with the traffic,
and a node doing compaction not being able to handle it.

/ Peter Schuller (@scode,

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