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https://issues.apache.org/jira/browse/SOLR-17076?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Smiley resolved SOLR-17076.
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Fix Version/s: 9.5
Resolution: Fixed
There's definitely a performance issue in such an environment (massive replica
count across the cluster). So much so that at Salesforce we switched to a
custom randomized placement plugin that ignores node stats altogether.
> Replica Placement could be slow for new collection creation with high amount
> of shards in a cluster with plenty of replicas
> ---------------------------------------------------------------------------------------------------------------------------
>
> Key: SOLR-17076
> URL: https://issues.apache.org/jira/browse/SOLR-17076
> Project: Solr
> Issue Type: Improvement
> Components: SolrCloud
> Affects Versions: 9.3
> Reporter: Patson Luk
> Priority: Major
> Fix For: 9.5
>
> Time Spent: 1h 50m
> Remaining Estimate: 0h
>
> It's found in our cluster with hundreds of thousands of replicas that
> collection creation is slow when the new collection has thousands of shards.
> In particular there are 4 mins+ computation time spent between the
> [collection initial
> creation|https://github.com/apache/solr/blob/ebcb3b92f6f0b2736d312a83de9d2ccadc0980aa/solr/core/src/java/org/apache/solr/cloud/api/collections/CreateCollectionCmd.java#L115]
> and [the SliceMutator creating
> slice|https://github.com/apache/solr/blob/ebcb3b92f6f0b2736d312a83de9d2ccadc0980aa/solr/core/src/java/org/apache/solr/cloud/api/collections/CreateCollectionCmd.java#L336]
> With some profiling and metrics checking, it appears that during those 4
> mins, almost all of the CPU time is spent in
> {{org.apache.solr.cluster.placement.plugins.OrderedNodePlacementPlugin$WeightedNode.getAllReplicasOnNode}}.
> For each new shard, it invokes this method to compute the weight which
> iterates on all collection and shard, with creation of a new replica set.
> This computation is costly for our environment based on the profiler and CPU
> metrics.
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