Info

On MongoDB 4.2/4.4 sharded clusters, the collStats command returns an error on a non-existent database but not on a non-existent collection within an existing database: >>> client.admin.command('buildInfo')['version'] '4.2.9' >>> client.core.test.insert_one({}) >>> client.core.list_collection_names() ['test'] >>> client.idontexist.command("collstats", 'idontexist', check=False) {'ok': 0.0, 'errmsg': 'database idontexist not found', 'code': 26, 'codeName': 'NamespaceNotFound', 'operationTime': Timestamp(1601349800, 22), '$clusterTime': {'clusterTime': Timestamp(1601349800, 22), 'signature': {'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'keyId': 0}}} >>> client.core.command("collstats", 'idontexist') {'sharded': False, 'primary': 'demo-set-0', 'indexDetails': {}, 'ns': 'core.idontexist', 'count': 0, 'size': 0, 'storageSize': 0, 'totalIndexSize': 0, 'indexSizes': {}, 'avgObjSize': 0.0, 'maxSize': 0, 'nindexes': 0, 'nchunks': 1, 'shards': {'demo-set-0': {'ns': 'core.idontexist', 'size': 0, 'count': 0, 'storageSize': 0, 'nindexes': 0, 'totalIndexSize': 0, 'indexDetails': {}, 'indexSizes': {}, 'scaleFactor': 1, 'ok': 1.0, '$gleStats': {'lastOpTime': {'ts': Timestamp(1601349779, 1), 't': 1}, 'electionId': ObjectId('7fffffff0000000000000001')}, 'lastCommittedOpTime': Timestamp(1601349809, 15), '$configServerState': {'opTime': {'ts': Timestamp(1601349809, 17), 't': 1}}, '$clusterTime': {'clusterTime': Timestamp(1601349809, 22), 'signature': {'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'keyId': 0}}, 'operationTime': Timestamp(1601349809, 15)}}, 'ok': 1.0, 'operationTime': Timestamp(1601349809, 15), '$clusterTime': {'clusterTime': Timestamp(1601349809, 22), 'signature': {'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'keyId': 0}}} This behavior is inconsistent. On 4.0 and earlier both scenarios result in an error: >>> client.admin.command('buildInfo')['version'] '4.0.20' >>> client.idontexist.command("collstats", 'idontexist', check=False) {'ok': 0.0, 'errmsg': 'database idontexist not found', 'code': 26, 'codeName': 'NamespaceNotFound', 'operationTime': Timestamp(1601350251, 2), '$clusterTime': {'clusterTime': Timestamp(1601350251, 2), 'signature': {'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'keyId': 0}}} >>> client.core.command("collstats", 'idontexist', check=False) {'ok': 0.0, 'errmsg': 'Collection [core.idontexist] not found.', 'code': 8, 'codeName': 'UnknownError', 'operationTime': Timestamp(1601350188, 1), '$clusterTime': {'clusterTime': Timestamp(1601350189, 1), 'signature': {'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'keyId': 0}}} Note that there seems to be another bug here. Notice that in 4.0.20 the second error code is UnknownError when it surely should be NamespaceNotFound. This is related to SERVER-50070 but not quite the same.

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shane.harvey commented on Tue, 29 Sep 2020 18:02:04 +0000: Yes the original ticket description only applies to sharded clusters. In MongoDB 4.0 both replica sets and sharded clusters return an error (although very strangely it's also missing an error code): >>> client.admin.command('buildInfo')['version'] '4.0.20' >>> client.admin.command('isMaster')['setName'] 'ce28483f-db76-419d-8edc-8ac409adce80' >>> client.core.list_collection_names() [] >>> client.core.test.insert_one({}) >>> client.idontexist.command("collstats", 'idontexist', check=False) {'ns': 'idontexist.idontexist', 'ok': 0.0, 'errmsg': 'Database [idontexist] not found.', 'operationTime': Timestamp(1601401804, 1), '$clusterTime': {'clusterTime': Timestamp(1601401804, 1), 'signature': {'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'keyId': 0}}} >>> client.core.command("collstats", 'idontexist', check=False) {'ns': 'core.idontexist', 'ok': 0.0, 'errmsg': 'Collection [core.idontexist] not found.', 'operationTime': Timestamp(1601401811, 1), '$clusterTime': {'clusterTime': Timestamp(1601401811, 1), 'signature': {'hash': b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'keyId': 0}}} Looking more into it I see this was changed in SERVER-29678. However I think SERVER-29678 only addressed the issue on mongod, not mongos. Can we make the behavior consistent between replica sets and sharded clusters? Can we also fix the missing/UnknownError error codes? daniel.gottlieb@10gen.com commented on Tue, 29 Sep 2020 14:41:32 +0000: shane.harvey when I run collStats on just a replica set, I receive an "ok" response on both: The database exists, but the collection doesn't exist. The database does not exist. I'm led to believe the error you're seeing when the database doesn't exist is specific to a sharded cluster? Am I correct in assuming you'd like to see standalones/replica sets/sharded clusters to all exhibit the same behavior? I'm going to speculatively assume the answers to those questions are yes and assign this to execution's backlog for triaging (I'm not exactly sure if a specific team owns collStats).

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