Patson Luk created SOLR-17076:
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Summary: Replica Placement could be slow for new collection with
high amount of shard in a cluster with plenty replicas
Key: SOLR-17076
URL: https://issues.apache.org/jira/browse/SOLR-17076
Project: Solr
Issue Type: Improvement
Security Level: Public (Default Security Level. Issues are Public)
Components: SolrCloud
Affects Versions: 9.3
Reporter: Patson Luk
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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