[SERVER-79914] CollectionRoutingInfoTargeter::targetInsert can incorrectly route a document missing _id Created: 10/Aug/23  Updated: 13/Dec/23  Resolved: 13/Dec/23

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: 7.3.0-rc0

Type: Bug Priority: Major - P3
Reporter: Kaitlin Mahar Assignee: Allison Easton
Resolution: Fixed Votes: 0
Labels: shardingemea-qw
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Assigned Teams:
Sharding EMEA
Backwards Compatibility: Fully Compatible
Operating System: ALL
Sprint: Sharding EMEA 2023-10-02, Sharding EMEA 2023-10-16, Sharding EMEA 2023-10-30, CAR Team 2023-11-13, CAR Team 2023-11-27, CAR Team 2023-12-11, CAR Team 2023-12-25
Participants:
Story Points: 2

 Description   

This is because the logic in ShardKeyPattern::extractShardKeyFromDoc will fill in BSON null for any value in the shard key pattern that is not found in the document.

This can cause a problem if a document to insert is passed to this method that does not already have an _id, and _id is in the shard key pattern. The document will then be routed to a shard based on an _id of BSON null. But once the document arrives on the shard, the shard will insert it, and give it a new _id, since it lacks one. And once it has a new _id, its value for the shard key has changed, and it may not be on the correct shard given its shard key.

This happens to not be a problem right now for the insert command, because mongos always adds _id to incoming insert command requests. But we noticed this problem with the new bulkWrite command where we weren't generating _id on mongos.

We will update the bulkWrite command to follow the same logic as insert to ensure there is always an _id, but it might be good to add some safeguard(s) around this. For example, maybe this method should error if _id is in the shard key pattern but not in the document.



 Comments   
Comment by Githook User [ 13/Dec/23 ]

Author:

{'name': 'Allison Easton', 'email': 'allison.easton@mongodb.com', 'username': 'allisoneaston'}

Message: SERVER-79914 CollectionRoutingInfoTargeter::targetInsert can incorrectly route a document missing _id

GitOrigin-RevId: 096f7f80ba889d2f64736fc53a48d6ecb6d1c73d
Branch: master
https://github.com/mongodb/mongo/commit/e111f9da9682e185e8c9fbc5f9e933f0689bf06e

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