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From "Jonathan Ellis (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-4839) Online toggle for node write-only status
Date Wed, 12 Jun 2013 22:38:20 GMT


Jonathan Ellis commented on CASSANDRA-4839:

Doesn't this approach mean that as soon as a compaction starts your severity will get set
to whatever the compaction calculated?  I think you need some kind of flag that says "this
is manually set, don't mess with it."
> Online toggle for node write-only status
> ----------------------------------------
>                 Key: CASSANDRA-4839
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Rick Branson
>            Priority: Minor
>         Attachments: 4839_revised.txt, 4839.txt
> It would be really great if users could disable/enable reads on a given node, while still
allowing write operations to take place. This would be similar to how we enable/disable thrift
and gossip using JMX.
> The scenario for using this is that often a node needs to be brought down for maintenance
for a few minutes, and while the node is catching up from hints, which can take 10-30 minutes
depending on write load, it will serve stale data. Do the math for a rolling restart of a
large cluster and you have potential windows of hours or days where a large amount of inconsistency
is surfacing.
> Avoiding this large time gap of inconsistency during regular maintenance alleviates concerns
about inconsistent data surfaced to users during normal, planned activities. While a read
consistency >ONE can indeed be used to prevent any inconsistency from the scenario above,
it seems ridiculous to always incur the cost to cover the 0.1% case.
> In addition, it would open up the ability for a node to (optionally) automatically "go
dark" for reads while it's receiving hints after joining the cluster or perhaps during repair.
These obviously have their own complications and justify separate tickets.

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