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https://issues.apache.org/jira/browse/SOLR-9014?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15270817#comment-15270817
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Scott Blum commented on SOLR-9014:
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I don't know... seems like a dicey game to try to ensure that no collection
node can ever exist without a state.json. Even the process of migrating state
format would have to be transactional. It seems really tricky to both get all
the edge cases right and convince ourselves there's never a legitimate use case
(like having a non-collection just for holding shared config).
I think what I would most be in favor of is deprecating the existing API and
return a Map<String, DocCollection> to at least avoid the cases where we're
doing double lookups today. Most callers are iterating over the returned set
and fetching individual DocCollections in a loop, which causes a second lookup,
which is the real problem. You can never avoid doing at least one lookup
anyway.
An alternate, wacky idea, is to do the same thing but return a custom Map
implementation that lazily determines the map contents.
> Deprecate and reduce usage of ClusterState methods which may make calls to ZK
> via the lazy collection reference
> ---------------------------------------------------------------------------------------------------------------
>
> Key: SOLR-9014
> URL: https://issues.apache.org/jira/browse/SOLR-9014
> Project: Solr
> Issue Type: Improvement
> Components: SolrCloud
> Reporter: Shalin Shekhar Mangar
> Fix For: 6.1, master
>
> Attachments: SOLR-9014.patch
>
>
> ClusterState has a bunch of methods such as getSlice and getReplica which
> internally call getCollectionOrNull that ends up making a call to ZK via the
> lazy collection reference. Many classes use these methods even though a
> DocCollection object is available. In such cases, multiple redundant calls to
> ZooKeeper can happen if the collection is not watched locally. This is
> especially true for Overseer classes which operate on all collections.
> We should audit all usages of these methods and replace them with calls to
> appropriate DocCollection methods.
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