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Date: Thu, 7 Apr 2011 17:24:05 +0000 (UTC)
From: "Peter Schuller (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Created] (CASSANDRA-2434) node bootstrapping can violate
 consistency
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node bootstrapping can violate consistency
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                 Key: CASSANDRA-2434
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2434
             Project: Cassandra
          Issue Type: Bug
    Affects Versions: 0.7.4
            Reporter: Peter Schuller


My reading (a while ago) of the code indicates that there is no logic involved during bootstrapping that avoids consistency level violations. If I recall correctly it just grabs neighbors that are currently up.

There are at least two issues I have with this behavior:

* If I have a cluster where I have applications relying on QUORUM with RF=3, and bootstrapping complete based on only one node, I have just violated the supposedly guaranteed consistency semantics of the cluster.

* Nodes can flap up and down at any time, so even if a human takes care to look at which nodes are up and things about it carefully before bootstrapping, there's no guarantee.

A complication is that not only does it depend on use-case where this is an issue (if all you ever do you do at CL.ONE, it's fine); even in a cluster which is otherwise used for QUORUM operations you may wish to accept less-than-quorum nodes during bootstrap in various emergency situations.

A potential easy fix is to have bootstrap take an argument which is the number of hosts to bootstrap from, or to assume QUORUM if none is given.

(A related concern is bootstrapping across data centers. You may *want* to bootstrap to a local node and then do a repair to avoid sending loads of data across DC:s while still achieving consistency. Or even if you don't care about the consistency issues, I don't think there is currently a way to bootstrap from local nodes only.)

Thoughts?


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