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https://issues.apache.org/jira/browse/SOLR-7571?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14566206#comment-14566206
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Vijay Sekhri commented on SOLR-7571:
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Ideally if a system cannot handle a high rate, it should fails early on by
letting the client know about the failure . In which case the client can mark
those failures and retry and adjust the rate in an adaptive and real time way.
Instead what happens currently is that the system does not report failure to
the client if the rate is too high even though internally it could not handle
the update to its replicas and therefore renders the whole cluster unstable. A
fail fast approach with acknowledgement back to the client can really help a
lot in this case.
> Return metrics with update requests to allow clients to self-throttle
> ---------------------------------------------------------------------
>
> Key: SOLR-7571
> URL: https://issues.apache.org/jira/browse/SOLR-7571
> Project: Solr
> Issue Type: Improvement
> Affects Versions: 4.10.3
> Reporter: Erick Erickson
> Assignee: Erick Erickson
>
> I've assigned this to myself to keep track of it, anyone who wants please
> feel free to take this.
> I've recently seen a setup with 10 shards and 4 replicas. The SolrJ client
> (and post.jar for json files for that matter) firehose updates (150 separate
> threads in total) at Solr. Eventually, replicas (not leaders) go into
> recovery and the state cascades and eventually the entire cluster becomes
> unusable. SOLR-5850 delays the behavior, but it still occurs. There are no
> errors in the follower's logs this is leader-initiated-recovery because of a
> timeout.
> I think the root problem is that the client is just sending too many requests
> to the cluster, and ConcurrentUpdateSolrClient/Server (used by the leader to
> distribute update requests to all the followers) (this was observed in Solr
> 4.10.3+). I see thread counts of 500+ when this happens.
> So assuming that this is the root cause, the obvious "cure" is "don't index
> that fast". This is unsatisfactory since "that fast" is variable, the only
> recourse is to set that threshold low enough that the Solr cluster isn't
> being driven as fast is it can be.
> We should provide some mechanism for having the client throttle itself. The
> number of outstanding update threads is one possibility. The client could
> then slow down sending updates to Solr.
> I'm not sure there's a good way to deal with this on the server. Once the
> timeout is encountered, you don't know whether the doc has actually been
> indexed on the follower (actually, in this case it _is_ indexed, it just take
> a while). Ideally we'd just manage it all magically, but an alternative to
> let clients dynamically throttle themselves seems do-able.
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