Shard_Merge , Shard_Filter, FETCH stages of execution plan

I understand use of following stages as below. But, could not understand use of Shard_Filter stage. Can you help me?
IXSCAN scans keys
FETCH retrieves document based on keys
SHARD_MERGE should combine results from multiple shards. Then, why does it shows execution time of this stage at every shard?

Hi @Prof_Monika_Shah and welcome to the MongoDB community forum!!

The following documentation for the explain results for MongoDB might help you with the explanations for the stages in detail.

With regard to your question, from the link above:

  • SHARD_MERGE for merging results from shards
  • SHARDING_FILTER for filtering out orphan documents from shards

Could you provide the output of db.collection.explain('executionStats') in question?

Best Regards