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  1. Python Driver
  2. PYTHON-1781

PyMongo 3.7 does not raise an error when attempting sharded transactions on 4.2

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • 3.7.2
    • 3.8
    • None
    • None

    Description

      The 4.0 transaction spec says:

      startTransaction SHOULD report an error if the driver can detect that transactions are not supported by the deployment. A deployment does not support transactions when the deployment does not support sessions, or maxWireVersion < 7, or the topology type is Sharded

      https://github.com/mongodb/specifications/blob/cf7248b2574b1a5397a6e18362acfe66f2b55a43/source/transactions/transactions.rst#starttransaction

      However, pymongo never implemented this check. When 3.7.2 runs a transaction against MongoDB 4.2, it will get an error like this on the first command that goes to a new mongos:

      {
        'ok': 0.0,
        'errmsg': 'cannot continue txnId -1 for session ... with txnId 1',
        'code': 251,
        'codeName': 'NoSuchTransaction',
        'errorLabels': ['TransientTransactionError']
      }
      

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              shane.harvey@mongodb.com Shane Harvey
              shane.harvey@mongodb.com Shane Harvey
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                Updated:
                Resolved: