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  1. Core Server
  2. SERVER-27283

Sharded aggregations that need merging should only consider for merging the shards that have documents to contribute

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      Even though a scatter-gather aggregation is sent to all shards, it may be the case that a small subset of shards have any results to contribute to the merge stage.

      In those cases it would be better for performance if we only considered for merge stage the shards that have documents to contribute to the merge phase.

      (This would require shards doing more work on the cursor before returning it to mongos for forwarding to selected merging shard).

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              Assignee:
              backlog-query-optimization Backlog - Query Optimization
              Reporter:
              asya Asya Kamsky
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