Caleb Rackliffe created CASSANDRA-17808:
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Summary: Optionally avoid hint transfer during decommission
Key: CASSANDRA-17808
URL: https://issues.apache.org/jira/browse/CASSANDRA-17808
Project: Cassandra
Issue Type: Improvement
Reporter: Caleb Rackliffe
Assignee: Caleb Rackliffe
Both because they aren’t strictly necessary to maintain consistency, and
because throttling induced by their rate-limiter (see
{{hinted_handoff_throttle}}) may stall progress, transferring hints during
decommission (specifically unbootstrap) rather than just pausing, disabling,
and truncating them probably doesn’t make sense. The only other concern would
be the BatchLog, which nominally depends on hint delivery to maintain its
"guarantees". However, during BatchLog replay on unbootstrap,
{{ReplayingBatch}} ignores batches older the gcgs anyway.
Here's a proposal from [~aleksey] that might strike a reasonable balance:
1.) We continue to transfer hints by default during decommission, but at a
higher rate. We could, for instance stop having {{DispatchHintsTask}} divide
its effective rate by the number of nodes in the cluster.
{noformat}
int nodesCount = Math.max(1,
StorageService.instance.getTokenMetadata().getAllEndpoints().size() - 1);
double throttleInBytes =
DatabaseDescriptor.getHintedHandoffThrottleInKiB() * 1024.0 / nodesCount;
this.rateLimiter = RateLimiter.create(throttleInBytes == 0 ?
Double.MAX_VALUE : throttleInBytes);
{noformat}
2.) We provide an option to simply avoid transferring hints during unbootstrap.
Even this would only take the BatchLog from "best effort" to "slightly less
effort" ;)
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