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  1. Core Server
  2. SERVER-31885

changeStream cursor is not returned on a mongos when the database does not exist

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • 3.6.0-rc3
    • 3.6.1, 3.7.1
    • Aggregation Framework
    • None
    • Fully Compatible
    • ALL
    • v3.6
    • Query 2017-12-18

    Description

      On a replica set a changeStream cursor can be created on a collection where the database does not exist yet:

      > db.dropDatabase()
      { "ok" : 1, "operationTime" : Timestamp(1510184057, 1) }
      > db.runCommand({"aggregate":"database-does-not-exist", "pipeline":[{'$changeStream': {}}], "cursor": {}})
      {
      	"cursor" : {
      		"firstBatch" : [ ],
      		"id" : NumberLong("5437951372965323737"),
      		"ns" : "test.database-does-not-exist"
      	},
      	"ok" : 1,
      	"operationTime" : Timestamp(1510184077, 1)
      }
      

      The same operation on a mongos does not return a cursor:

      MongoDB Enterprise mongos> db.dropDatabase()
      {
      	"dropped" : "test",
      	"ok" : 1,
      	"$clusterTime" : {
      		"clusterTime" : Timestamp(1510184413, 9),
      		"signature" : {
      			"hash" : BinData(0,"lFkT1OPozsQoRVqqU/5bXxUNhng="),
      			"keyId" : NumberLong("6486191337619062789")
      		}
      	},
      	"operationTime" : Timestamp(1510184413, 9)
      }
      MongoDB Enterprise mongos> db.runCommand({"aggregate":"database-does-not-exist", "pipeline":[{'$changeStream': {}}], "cursor": {}})
      {
      	"result" : [ ],
      	"cursor" : {
      		"id" : NumberLong(0),
      		"ns" : "test.database-does-not-exist",
      		"firstBatch" : [ ]
      	},
      	"ok" : 1,
      	"$clusterTime" : {
      		"clusterTime" : Timestamp(1510184417, 1),
      		"signature" : {
      			"hash" : BinData(0,"KsuOoKtQYUkl2peKWjMv4kJHzzE="),
      			"keyId" : NumberLong("6486191337619062789")
      		}
      	},
      	"operationTime" : Timestamp(1510184417, 1)
      }
      

      This is surprising when combined with the fact that wired tiger drops databases when there are no more collections.

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              bernard.gorman@mongodb.com Bernard Gorman
              shane.harvey@mongodb.com Shane Harvey
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                Created:
                Updated:
                Resolved: