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From Peter Schuller <peter.schul...@infidyne.com>
Subject Re: Node repair questions
Date Mon, 11 Jul 2011 23:01:44 GMT
(not answering (1) right now, because it's more involved)

> 2. Does a Nodetool Repair block any reads and writes on the node,
> while the repair is going on ? During repair, if I try to do an
> insert, will the insert wait for repair to complete first ?

It doesn't imply any blocking. It's roughly similar to compaction in
its impact on nodes; in addition when data is streamed (if any) the
impact should be similar to node bootstrapping.

> 3. I read that repair can impact your workload as it causes additional
> disk and cpu activity. But any details of the impact mechanism and any
> ballpark on how much the read/write performance deteriorates ?

The compaction part will have an impact similar to regular compaction
except it's read-only (no writing of new sstables). It is subject to
compaction throttling if you run a version of Cassandra with
compaction throttling.

Streaming causes disk/networking load and is not yet rate limited like
compaction.

In addition be aware that repair can cause disk space usage to
temporarily increase if there are significant differences to be
repaired.

-- 
/ Peter Schuller

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