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From Carl Mueller <carl.muel...@smartthings.com.INVALID>
Subject Re: postmortem on 2.2.13 scale out difficulties
Date Wed, 12 Jun 2019 16:35:29 GMT
We only were able to scale out four nodes and then failures started
occurring, including multiple instances of nodes joining a cluster without
streaming.

Sigh.

On Tue, Jun 11, 2019 at 3:11 PM Carl Mueller <carl.mueller@smartthings.com>
wrote:

> We had a three-DC (asia-tokyo/europe/us) cassandra 2.2.13 cluster, AWS,
> IPV6
>
> Needed to scale out the asia datacenter, which was 5 nodes, europe and us
> were 25 nodes
>
> We were running into bootstrapping issues where the new node failed to
> bootstrap/stream, it failed with
>
> "java.lang.RuntimeException: A node required to move the data consistently
> is down"
>
> ...even though they were all up based on nodetool status prior to adding
> the node.
>
> First we increased the phi_convict_threshold to 12, and that did not help.
>
> CASSANDRA-12281 appeared similar to what we had problems with, but I don't
> think we hit that. Somewhere in there someone wrote
>
> "For us, the workaround is either deleting the data (then bootstrap
> again), or increasing the ring_delay_ms. And the larger the cluster is, the
> longer ring_delay_ms is needed. Based on our tests, for a 40 nodes cluster,
> it requires ring_delay_ms to be >50seconds. For a 70 nodes cluster,
> >100seconds. Default is 30seconds."
>
> Given the WAN nature or our DCs, we used ring_delay_ms to 100 seconds and
> it finally worked.
>
> side note:
>
> During the rolling restarts for setting phi_convict_threshold we observed
> quite a lot of status map variance between nodes (we have a program to poll
> all of a datacenter or cluster's view of the gossipinfo and statuses. AWS
> appears to have variance in networking based on the phi_convict_threshold
> advice, I'm not sure if our difficulties were typical in that regard and/or
> if our IPV6 and/or globally distributed datacenters were exacerbating
> factors.
>
> We could not reproduce this in loadtest, although loadtest is only eu and
> us (but is IPV6)
>

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