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From "Peter Schuller (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-2434) node bootstrapping can violate consistency
Date Thu, 07 Apr 2011 17:24:05 GMT
node bootstrapping can violate consistency
------------------------------------------

                 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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