[ 
https://issues.apache.org/jira/browse/CASSANDRA-13910?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16433556#comment-16433556
 ] 

Sylvain Lebresne commented on CASSANDRA-13910:
----------------------------------------------

bq. Turning on [~slebresne] signal.

I actually personally prefer being clear and throw an exception. As a user, 
what I would find rude, is if I'm too easily misled to believe one of my action 
has worked when it has in fact no action, and just having a warning make that 
more likely. If something has been removed, I don't find it rude to get an 
exception, I find it honest and helpful. It's a preference though at the end of 
the day, so just giving my 2 cents but not pushing more than that.

bq. The WARN on using old things is how we have done this in the past.

I'm sure your memory is better than me, but didn't we mostly used warnings when 
we deprecated something? That is, we had a release where the old settings were 
still working but were warning, and when it stopped working we removed it?



> Remove read_repair_chance/dclocal_read_repair_chance
> ----------------------------------------------------
>
>                 Key: CASSANDRA-13910
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13910
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Sylvain Lebresne
>            Assignee: Aleksey Yeschenko
>            Priority: Minor
>             Fix For: 4.0
>
>
> First, let me clarify so this is not misunderstood that I'm not *at all* 
> suggesting to remove the read-repair mechanism of detecting and repairing 
> inconsistencies between read responses: that mechanism is imo fine and 
> useful.  But the {{read_repair_chance}} and {{dclocal_read_repair_chance}} 
> have never been about _enabling_ that mechanism, they are about querying all 
> replicas (even when this is not required by the consistency level) for the 
> sole purpose of maybe read-repairing some of the replica that wouldn't have 
> been queried otherwise. Which btw, bring me to reason 1 for considering their 
> removal: their naming/behavior is super confusing. Over the years, I've seen 
> countless users (and not only newbies) misunderstanding what those options 
> do, and as a consequence misunderstand when read-repair itself was happening.
> But my 2nd reason for suggesting this is that I suspect 
> {{read_repair_chance}}/{{dclocal_read_repair_chance}} are, especially 
> nowadays, more harmful than anything else when enabled. When those option 
> kick in, what you trade-off is additional resources consumption (all nodes 
> have to execute the read) for a _fairly remote chance_ of having some 
> inconsistencies repaired on _some_ replica _a bit faster_ than they would 
> otherwise be. To justify that last part, let's recall that:
> # most inconsistencies are actually fixed by hints in practice; and in the 
> case where a node stay dead for a long time so that hints ends up timing-out, 
> you really should repair the node when it comes back (if not simply 
> re-bootstrapping it).  Read-repair probably don't fix _that_ much stuff in 
> the first place.
> # again, read-repair do happen without those options kicking in. If you do 
> reads at {{QUORUM}}, inconsistencies will eventually get read-repaired all 
> the same.  Just a tiny bit less quickly.
> # I suspect almost everyone use a low "chance" for those options at best 
> (because the extra resources consumption is real), so at the end of the day, 
> it's up to chance how much faster this fixes inconsistencies.
> Overall, I'm having a hard time imagining real cases where that trade-off 
> really make sense. Don't get me wrong, those options had their places a long 
> time ago when hints weren't working all that well, but I think they bring 
> more confusion than benefits now.
> And I think it's sane to reconsider stuffs every once in a while, and to 
> clean up anything that may not make all that much sense anymore, which I 
> think is the case here.
> Tl;dr, I feel the benefits brought by those options are very slim at best and 
> well overshadowed by the confusion they bring, and not worth maintaining the 
> code that supports them (which, to be fair, isn't huge, but getting rid of 
> {{ReadCallback.AsyncRepairRunner}} wouldn't hurt for instance).
> Lastly, if the consensus here ends up being that they can have their use in 
> weird case and that we fill supporting those cases is worth confusing 
> everyone else and maintaining that code, I would still suggest disabling them 
> totally by default.



--
This message was sent by Atlassian JIRA
(v7.6.3#76005)

---------------------------------------------------------------------
To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org
For additional commands, e-mail: commits-h...@cassandra.apache.org

Reply via email to