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From "Aleksey Yeschenko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8368) Consider not using hints for batchlog replay, in any capacity
Date Fri, 31 Jul 2015 16:03:04 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14649407#comment-14649407
] 

Aleksey Yeschenko commented on CASSANDRA-8368:
----------------------------------------------

And assume that CASSANDRA-7237 is committed, because it soon will be, while devising a new
procedure.

> Consider not using hints for batchlog replay, in any capacity
> -------------------------------------------------------------
>
>                 Key: CASSANDRA-8368
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8368
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Aleksey Yeschenko
>             Fix For: 3.0.0 rc1
>
>
> Currently, when replaying a batch, if a request times out, we simply write a hint for
it and call it a day.
> It's simple, but it does tie us to hints, which some people prefer to disable altogether
(and some still will even after CASSANDRA-6230).
> It also potentially violates the consistency level of the original request.
> As an alternative, once CASSANDRA-7237 is complete, I suggest we stop relying on hints
at all, and do this instead:
> 1. Store the consistency level as batch metadata
> 2. On replay, hint in case of a timeout, but not if the node is down as per FD
> 3. If CL is met, consider the batch replayed and discard it, but not account the hints
towards CL (as per usual write patch), unless CL.ANY is being used
> 4. If CL is *not* met, write a new batch with contents of the current one, but with timeuuid
set in the future, for later replay (delayed by fixed configurable time or exponentially backed
off). With that new batch store the list of nodes we've delivered the hint to, so that next
time we replay it we don't waste writes.



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