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Type:
Improvement
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Resolution: Fixed
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Priority:
Major - P3
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Affects Version/s: None
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Component/s: None
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Labels:None
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Fully Compatible
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QE 2022-06-13
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15
The shell currently has two separate paths for running find commands: the DBCommandCursor path which is implemented primarily in the JavaScript layer, and the C++ native path. Historically, the former was used for find commands and the latter was used for legacy OP_QUERY find. However, OP_QUERY find is no longer supported by the shell. The only cases in which the C++ path currently get used are for queries against the "$cmd" namespace and for exhaust queries.
The C++ native path is broken when given a negative limit. This trips a tassert in the shell. Examples:
MongoDB Enterprise > db.$cmd.foo.find().limit(-3)
{"t":{"$date":"2022-06-08T14:47:06.679Z"},"s":"E", "c":"ASSERT", "id":4457000, "ctx":"js","msg":"Tripwire assertion","attr":{"error":{"code":5746103,"codeName":"Location5746103","errmsg":"DBClientCursor limit must be non-negative"},"location":"{fileName:\"src/mongo/client/dbclient_cursor.cpp\", line:669, functionName:\"operator()\"}"}}
Error: DBClientCursor limit must be non-negative
MongoDB Enterprise > db.$cmd.foo.findOne()
{"t":{"$date":"2022-06-08T14:47:11.579Z"},"s":"E", "c":"ASSERT", "id":4457000, "ctx":"js","msg":"Tripwire assertion","attr":{"error":{"code":5746103,"codeName":"Location5746103","errmsg":"DBClientCursor limit must be non-negative"},"location":"{fileName:\"src/mongo/client/dbclient_cursor.cpp\", line:669, functionName:\"operator()\"}"}}
Error: DBClientCursor limit must be non-negative :
DBQuery.prototype._exec@src/mongo/shell/query.js:149:40
DBQuery.prototype.hasNext@src/mongo/shell/query.js:302:10
DBCollection.prototype.findOne@src/mongo/shell/collection.js:267:17
@(shell):1:13
MongoDB Enterprise > db.c.find().addOption(DBQuery.Option.exhaust).limit(-10)
{"t":{"$date":"2022-06-08T14:47:31.846Z"},"s":"E", "c":"ASSERT", "id":4457000, "ctx":"js","msg":"Tripwire assertion","attr":{"error":{"code":5746103,"codeName":"Location5746103","errmsg":"DBClientCursor limit must be non-negative"},"location":"{fileName:\"src/mongo/client/dbclient_cursor.cpp\", line:669, functionName:\"operator()\"}"}}
Error: DBClientCursor limit must be non-negative
The work for this ticket is to fix the shell so that these queries work as expected, which will resolve the linked build failure.
As far as I can tell, there is no reason to use the C++ path for "$cmd" namespaces. I think this relates to some old behavior around pseudo-commands which is no longer relevant. We should just use the normal DBCommandCursor path in this case.
We still need to use the C++ native path for exhaust queries. (Note, however, that SERVER-20770 and SERVER-58491 suggest consolidating the two code paths in the shell.) A good fix for this problem would be to add support for exhaust in the new DBClientBase::find() API and then migrate the shell from DBClientBase::query_DEPRECATED() to DBClientBase::find().
- is related to
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SERVER-58491 Consolidate the C++ native cursor implementation with the DBCommandCursor-based one in the shell js
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- Backlog
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- Backlog
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- Closed
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- related to
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SERVER-66047 Parameter 'limit' is not supported for exhaust queries in Mongo Shell
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- Closed
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