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  1. Core Server
  2. SERVER-53638

Enable pushdown of config.cache.chunks $lookup through $sort

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    • Backwards Compatibility:
      Fully Compatible
    • Sprint:
      Query Optimization 2021-02-22, Query Optimization 2021-03-08, Query Optimization 2021-03-22, Query Optimization 2021-04-05, Query Optimization 2021-04-19

      Description

      As part of a resharding operation we issue a pipeline with a $sort followed by a $lookup on config.cache.chunks. For efficiency and resumability, we need each shard to provide things in a sorted order and also perform the $lookup. Today this doesn't work because the $sort forces a split of a sharded pipeline and does not push the $lookup into the shards part. For this particular $lookup, we know it is safe to run it in parallel, so we should be able to push it into the shards pipeline.

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              Assignee:
              yuhong.zhang Yuhong Zhang
              Reporter:
              charlie.swanson Charlie Swanson
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