[SERVER-66824] Secondary's query targeting bug in Altas Search Index Created: 27/May/22  Updated: 02/Jun/22  Resolved: 02/Jun/22

Status: Closed
Project: Core Server
Component/s: Index Maintenance, Replication, Text Search
Affects Version/s: 4.4.14, 5.0.8
Fix Version/s: None

Type: Bug Priority: Critical - P2
Reporter: 규형 이 Assignee: Chris Kelly
Resolution: Done Votes: 0
Labels: Bug, atlas-search, queryTargeting, search, search-index
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified
Environment:

MongoDB Atlas 4.4.14 M40
ReplicaSet(Primary-Secondary-Secondary)


Attachments: PNG File metrics.png    
Operating System: ALL
Participants:

 Description   

Hello.
I am using the M40 cluster of MongoDB Atlas 4.4.14.

I'm inserting 1.5 million to 2 million documents into a new collection every hour, and I've confirmed that the Query Targeting: Scanned Objects / Returned Has Gone 1000 alarm occurs every hour in the secondary of the cluster.

I didn't understand this, so I did some tests
We have confirmed that the data change is caused by Atlas Search Index that exists in a different collection from the command operation collection.

I think the update should occur only for the data changes in the collection where Search Index exists (to prevent unnecessary secondary load and unnecessary alerting)

Currently, I use readPreference=secondary in the application for load balancing, but I think that the above operation could cover the colscan caused by lack of index.

In many enterprise areas using MongoDB Atlas, we believe that the readPreference=secondary option will be used for load balancing, which requires corrective action.

It took almost a month to investigate the cause of this phenomenon, so I would like you to seriously take action on the issue.

(We have also confirmed that this is the same for clusters of versions 4.4.14 and 5.0.8)

Thank you.
Have a nice day.



 Comments   
Comment by Chris Kelly [ 02/Jun/22 ]

Hello,

Thanks for your report on this. To inform our Atlas team of issues you are having or feature requests you'd like to suggest, please reach out to the Atlas support team via Intercom first. You can do this by clicking the round green button at the bottom right of the cluster view page in Atlas. This will be the best first step for looking into the problem further.

Regards,
Christopher

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