[SERVER-51463] currentOp command silently fails to apply match conditions when result is truncated Created: 09/Oct/20  Updated: 06/Dec/22

Status: Backlog
Project: Core Server
Component/s: Querying
Affects Version/s: 4.2.9
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Tommaso Tocci Assignee: Backlog - Query Execution
Resolution: Unresolved Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Related
related to SERVER-51450 Use new $currentOp aggregation pipeli... Closed
related to SERVER-47513 killop.js should handle truncated com... Closed
related to SERVER-47603 Rewrite db.currentOp() shell helper i... Closed
related to SERVER-51102 Use new $currentOp aggregation pipeli... Closed
Assigned Teams:
Query Execution
Operating System: ALL
Steps To Reproduce:

Please refer to these tickets SERVER-51450, SERVER-51102

Participants:

 Description   

If the result of the currentOp command gets truncated, the command fails to apply the match conditions received.

The currentOp command has been deprecated in 3.6 in favor of the new $currentOp aggregation stage, due to the response size limitation. The problem is that we are still extensively relying on the currentOp command in our javascript test and recently some tests that were trying to match a count command started failing (SERVER-51450, SERVER-51102).

One strange thing that I've noticed debugging those failure is that the result of the currentOp command got truncated even if it didn't reached 16MB as described in our docs.

The other problem is that the command failed to apply the match conditions silently without any warning or error.

If we can't rely on this command anymore we should change all our tests to use the new $currentOp pipeline stage, or at least make it evident that they are failing for this reason.

Also if this is not a bug we should mention in the documentation that currentOp can fail to apply match conditions when the result gets truncated.



 Comments   
Comment by Craig Homa [ 11/Nov/20 ]

Moving to the backlog as we aren't intending to fix this as we plan to deprecate the currentOp() command in favor of the $currentOp aggregation stage.

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