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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 17:48:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14649534#comment-14649534
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Aleksey Yeschenko commented on CASSANDRA-8368:
----------------------------------------------

bq. So you mean the hints will eventually be replayed even after max_hint_window_in_ms goes
by? Or just that you will store a hint for it after max_hint_window_in_ms?

You misunderstand what {{max_hint_window_in_ms}} means. It's not about replay, it's only about
storing or not storing a hint in the first place. Batchlog-created hints will always be stored.

Whether or not they get replayed in the end depends solely on hint's TTL (but that same semantics
is in place for BL entires, they have the same TTL).

> 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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