[SERVER-39143] Add noop-event to Change stream Created: 23/Jan/19  Updated: 28/Jan/19  Resolved: 28/Jan/19

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

Type: Improvement Priority: Major - P3
Reporter: Artem Assignee: Bernard Gorman
Resolution: Duplicate Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Duplicate
duplicates SERVER-35740 Report high-water-mark resume token w... Closed
Sprint: Query 2019-02-11
Participants:

 Description   

When you listening changeStream for collection with rare updates, you have not any knowledge about:

  • you don't reciving event because nothing happens or somethins broken?
  • what processing events delay do you have (you can get unpredictable delay on changeStream resuming)?

Also you can't update refresh token without receiving changeStream event.

So, I think should be some `noop` event for changeStream (optional or with configurable period).



 Comments   
Comment by Bernard Gorman [ 28/Jan/19 ]

Hi bozaro,

Many thanks for your comments, and for highlighting this issue. As it happens, we are currently in the process of implementing exactly the functionality you describe. The work involved in doing so is tracked under the umbrella ticket SERVER-35740.

In broad terms, this project will ensure that every change stream batch returned from the server, whether empty or not, will include a resume token indicating the latest point from which it is safe to resume the stream. Even when the stream is not returning any events, the so-called "high water mark" token will continue to advance over time. In cases where a stream is waiting for events that occur very infrequently, therefore, your application will both be able to verify that the stream is still actively monitoring the collection, and it will be able to update its resume token without having to wait until the next event.

Since we already have a ticket to track this work, I'm going to close this ticket as a duplicate of SERVER-35740. Please feel free to set yourself as a Watcher on that ticket, and to ask any further questions you may have!

Best regards,
Bernard

Comment by Ramon Fernandez Marina [ 23/Jan/19 ]

Thanks for your report bozaro, sending it to the Query team for consideration.

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