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https://issues.apache.org/jira/browse/SOLR-7191?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15353362#comment-15353362
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Erick Erickson commented on SOLR-7191:
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IIUC, the whole watcher thing is replica based. So N replicas for the same
collection in the same JVM register N watchers.
If that's true, does it make sense to think about watchers being set per
_collection_ in a JVM rather than per _replica_? I admit I'm completely
ignorant of the nuances here. It also wouldn't make any difference in a
collection where each instance hosted exactly one replica per collection, but
practically I'm not sure there's anything we can do about that anyway.
Although it seems that each replica could be an Observer for a given collection
(watcher at the JVM level?) without doing much violence to the current
architecture. Or maybe it'd just be simpler to have the replicas get their
state information from some kind of cache maintained at the JVM level where the
cache was updated via watcher. I admit I'm talking through my hat here. Maybe
there should be a JIRA to discuss this?
> Improve stability and startup performance of SolrCloud with thousands of
> collections
> ------------------------------------------------------------------------------------
>
> Key: SOLR-7191
> URL: https://issues.apache.org/jira/browse/SOLR-7191
> Project: Solr
> Issue Type: Bug
> Components: SolrCloud
> Affects Versions: 5.0
> Reporter: Shawn Heisey
> Assignee: Shalin Shekhar Mangar
> Labels: performance, scalability
> Attachments: SOLR-7191.patch, SOLR-7191.patch, SOLR-7191.patch,
> SOLR-7191.patch, SOLR-7191.patch, SOLR-7191.patch, SOLR-7191.patch,
> lots-of-zkstatereader-updates-branch_5x.log
>
>
> A user on the mailing list with thousands of collections (5000 on 4.10.3,
> 4000 on 5.0) is having severe problems with getting Solr to restart.
> I tried as hard as I could to duplicate the user setup, but I ran into many
> problems myself even before I was able to get 4000 collections created on a
> 5.0 example cloud setup. Restarting Solr takes a very long time, and it is
> not very stable once it's up and running.
> This kind of setup is very much pushing the envelope on SolrCloud performance
> and scalability. It doesn't help that I'm running both Solr nodes on one
> machine (I started with 'bin/solr -e cloud') and that ZK is embedded.
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