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From "Jonathan Ellis (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-2034) Make Read Repair unnecessary when Hinted Handoff is enabled
Date Sun, 14 Aug 2011 03:25:27 GMT


Jonathan Ellis commented on CASSANDRA-2034:

I don't think keeping passing a list of unavailableEndpoints everywhere is actually necessary.
 I may be missing a use case, but what I see is

- in sendToHintedEndpoints
- in assureSufficientLiveNodes implementation

Both of which can be replaced in a straightforward manner with FailureDetector calls.  (Note
that it is not necessary for FD state to remain unchanged between assureSufficient and sending.)

In fact using the same list in both places is a bug: assureSufficient only cares about what
FD thinks, so mixing hinted-handoff-enabledness in as getUnavailableEndpoints does will cause
assureSufficient to return false positives w/ HH off.

So I'd make assureSufficient use FD directly, and sendTHE use FD + HH state.  Bonus: no List
allocation in the common case of "everything is healthy."

> Make Read Repair unnecessary when Hinted Handoff is enabled
> -----------------------------------------------------------
>                 Key: CASSANDRA-2034
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Patricio Echague
>             Fix For: 1.0
>         Attachments: 2034-formatting.txt, CASSANDRA-2034-trunk-v10.patch, CASSANDRA-2034-trunk-v11.patch,
CASSANDRA-2034-trunk-v11.patch, CASSANDRA-2034-trunk-v12.patch, CASSANDRA-2034-trunk-v13.patch,
CASSANDRA-2034-trunk-v2.patch, CASSANDRA-2034-trunk-v3.patch, CASSANDRA-2034-trunk-v4.patch,
CASSANDRA-2034-trunk-v5.patch, CASSANDRA-2034-trunk-v6.patch, CASSANDRA-2034-trunk-v7.patch,
CASSANDRA-2034-trunk-v8.patch, CASSANDRA-2034-trunk-v9.patch, CASSANDRA-2034-trunk.patch
>   Original Estimate: 8h
>  Remaining Estimate: 8h
> Currently, HH is purely an optimization -- if a machine goes down, enabling HH means
RR/AES will have less work to do, but you can't disable RR entirely in most situations since
HH doesn't kick in until the FailureDetector does.
> Let's add a scheduled task to the mutate path, such that we return to the client normally
after ConsistencyLevel is achieved, but after RpcTimeout we check the responseHandler write
acks and write local hints for any missing targets.
> This would making disabling RR when HH is enabled a much more reasonable option, which
has a huge impact on read throughput.

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