Shard routing key of issue documents is the project uuid. It allows to group all the issues of a project in the same shard so that performances of search requests are better when filtering on a project :
- only a single shard is requested
- only a single thread is required from search pools
- less CPU consumption
- less network usage (only one node is requested)
Elasticsearch request must be restricted to a subset of shards when condition on project UUIDs is set. Because sticky facets may involve all projects, this optimization must not be enabled when facets are requested.