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https://issues.apache.org/jira/browse/SOLR-9014?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15257276#comment-15257276
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Scott Blum commented on SOLR-9014:
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Yes, unfortunately. ClusterState.collectionStates is driven (in part) by
/solr/collections/<children>. In particular, if foo unwatched,
/solr/collections/foo exists, but /solr/collections/foo/state.json does NOT
exist, then the collection will appear in collectionStates as a
LazyCollectionRef, but it won't resolve to a DocCollection since there's no
state.json. We don't poll or watch for the existence of the state.json for
non-watched collections.
Watched collections don't have this problem, due to how interestingCollections
vs. watchedCollections is handled in ZkStateReader.
We should figure out if there's a better API for ClusterState to handle this
more efficiently. If you naively remove the guard in
ClusterState.getCollections(), what will happen is a lot of calling code will
break. For example, in Assign.getNodeNameVsShardCount(), the caller loops over
the returned set of collection names, calling
clusterState.getCollection(collectionName) and expecting the result to be
non-null. We would either need to update all those callers to check, or else
have LazyCollectionRef.get() return an empty DocCollection if the node doesn't
exist.
> 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: master, 6.1
>
> 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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