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Type:
Task
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Resolution: Won't Fix
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: manual
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Labels:None
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0.1
Scope of changes:
Previously, a $changeStream could be opened on a namespace before the associated database had been created. On a replica set, this would produce a valid $changeStream cursor; on a mongoS, however, it would return an empty, closed cursor which could not be used thereafter.
After this commit, a $changeStream can still be opened on a collection that does not yet exist provided that the database does exist. Attempting to open a $changeStream on a non-existent database results in a 'NamespaceNotFound' exception on both replica set and mongoS.
Impact to other docs outside of this product:
MVP:
Resources:
Engineering Ticket Description:
On a replica set a changeStream cursor can be created on a collection where the database does not exist yet:
> db.dropDatabase()
{ "ok" : 1, "operationTime" : Timestamp(1510184057, 1) }
> db.runCommand({"aggregate":"database-does-not-exist", "pipeline":[{'$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.
- documents
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SERVER-31885 changeStream cursor is not returned on a mongos when the database does not exist
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- Closed
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