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https://issues.apache.org/jira/browse/SOLR-6629?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17951509#comment-17951509
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David Smiley commented on SOLR-6629:
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bq. saves a number of ZK "exists" checks
A node only _needs_ to know about the collections that it's hosting replicas
for. Requests are generally routed well (by a CloudSolrClient) and so nodes
handling a request will already know that the collection exists. The other
scenarios are Overseer or overseer-like operations, which happen (or can be
arranged to happen) on one node; so that node ends up being fully aware of
everything. It's not the end of the world if ZK does need to be queried; it's
a HA in-memory service.
Removing CollectionsChildWatcher isn't particularly simple because it's
intertwined with assumptions of ClusterState being a fully aware of everything.
It needs to be cache like. [~aparnasuresh] might advise on further aspects if
desired.
> Watch /collections zk node on all nodes
> ---------------------------------------
>
> Key: SOLR-6629
> URL: https://issues.apache.org/jira/browse/SOLR-6629
> Project: Solr
> Issue Type: Improvement
> Components: SolrCloud
> Reporter: Shalin Shekhar Mangar
> Assignee: Shalin Shekhar Mangar
> Priority: Major
> Fix For: 5.4, 6.0
>
> Attachments: SOLR-6629-new.patch, SOLR-6629.patch, SOLR-6629.patch,
> SOLR-6629.patch, SOLR-6629.patch, SOLR-6629.patch
>
>
> The main clusterstate.json is refreshed/used as a poor substitute for
> informing all nodes about new or deleted collections even when the collection
> being created or deleted has state format > 1. When we move away from state
> format 1 then we should do away with this workaround and start watching the
> /collections zk node on all nodes.
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