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https://issues.apache.org/jira/browse/CASSANDRA-180?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jonathan Ellis updated CASSANDRA-180:
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Attachment: 180-v2.patch
Reducing the responseCount is going to break things, since that's used for
determining when a successful quorum has been reached.
Say you have a 5 node cluster and a replication factor of 3. But there is a
network split and the node a client is talking to can only see itself. With
your patch it would start up a QRH with a RC of 1, get the ack, and report that
the write was successful. But we've just sliently violated our promise of
quorum consistency (at least 2 nodes).
The existing code is optimal for when a write succeeeds -- as soon as a quorum
is reached it returns, w/o waiting for any more responses that may or may not
come. The only problem is that it will wait for timeout when it is impossible
for a write to reach quorum b/c there are not enough nodes. I've attached a
patch that addresses that problem. What do you think?
(Note that we don't need to try to solve the problem of "what if at the
beginning of a write there are enough nodes to reach quorum, but partway
through we get a nack from a node making it impossible" b/c nodes only ack
success, they don't nack failure. And making them do so adds more complication
than it is worth for such an uncommon case.)
> Blocking insert may have fewer responses than replication factor
> ----------------------------------------------------------------
>
> Key: CASSANDRA-180
> URL: https://issues.apache.org/jira/browse/CASSANDRA-180
> Project: Cassandra
> Issue Type: Bug
> Affects Versions: 0.3
> Reporter: Jun Rao
> Assignee: Jun Rao
> Priority: Minor
> Attachments: 180-v2.patch, issue180.patchv1
>
>
> Currently, block_insert always assumes the number of responses equals the
> replication factor. However, for a small cluster (e,g, 1 node) and/or when
> failure occurs, the number of responses could be fewer than the replication
> factor.
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