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From "Kurt Greaves (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-13851) Allow existing nodes to use all peers in shadow round
Date Wed, 01 Nov 2017 10:27:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-13851?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16233892#comment-16233892
] 

Kurt Greaves commented on CASSANDRA-13851:
------------------------------------------

|[dtest|https://github.com/apache/cassandra-dtest/compare/master...kgreav:13851]|[3.11|https://github.com/apache/cassandra/compare/cassandra-3.11...kgreav:3.11-13851]|

Current changes pass through whatever peers exist in system.peers to the shadow round and
will only use them if the first round of gossips to the seeds fail. So it will still try the
seeds first, it's just if the shadow round goes longer than 5 seconds will peers be included.
This allows a node to start if only peers are alive.
It also allows a node that doesn't need to bootstrap to start, even if it couldn't contact
any peers or seeds. 

>From what I can tell this works but open to ideas on other test cases/obvious things I've
missed.

FWIW this also passed all the bootstrap dtests, if that means anything.

> Allow existing nodes to use all peers in shadow round
> -----------------------------------------------------
>
>                 Key: CASSANDRA-13851
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13851
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Lifecycle
>            Reporter: Kurt Greaves
>            Priority: Major
>             Fix For: 3.11.x, 4.x
>
>
> In CASSANDRA-10134 we made collision checks necessary on every startup. A side-effect
was introduced that then requires a nodes seeds to be contacted on every startup. Prior to
this change an existing node could start up regardless whether it could contact a seed node
or not (because checkForEndpointCollision() was only called for bootstrapping nodes). 
> Now if a nodes seeds are removed/deleted/fail it will no longer be able to start up until
live seeds are configured (or itself is made a seed), even though it already knows about the
rest of the ring. This is inconvenient for operators and has the potential to cause some nasty
surprises and increase downtime.
> One solution would be to use all a nodes existing peers as seeds in the shadow round.
Not a Gossip guru though so not sure of implications.



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