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  1. Core Server
  2. SERVER-27438

Legacy query via mongos drops $comment

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • 3.4.0
    • 3.4.2, 3.5.2
    • Querying
    • None
    • Major Change
    • ALL
    • v3.4, v3.2
    • Hide

      1. Spin up a 3.4 sharded cluster
      2. Connect to a mongos with a 3.0.x shell, or use db.getMongo().forceReadMode("legacy")
      3. Issue a find with a comment, e.g. db.coll.find({...}).comment("TESTCOMMENT")
      4. Examine the resulting operation in currentOp or the profiler/logs

      Show
      1. Spin up a 3.4 sharded cluster 2. Connect to a mongos with a 3.0.x shell, or use db.getMongo().forceReadMode("legacy") 3. Issue a find with a comment, e.g. db.coll.find({...}).comment("TESTCOMMENT") 4. Examine the resulting operation in currentOp or the profiler/logs
    • Query 2017-01-23

    Description

      When a legacy query is issued to a mongos with a $comment meta-operator attached, the comment will be dropped before the query is forwarded. This is because the query is transformed to a find command for the shards, but the $comment field is not parsed from the original legacy object and is therefore not added to the final command. A legacy query on a mongod retains the comment since no transformation occurs. This behaviour has been present since 3.2.

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              bernard.gorman@mongodb.com Bernard Gorman
              bernard.gorman@mongodb.com Bernard Gorman
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                Updated:
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