[SERVER-54890] Disable background validation and dbHash checks on capped collections in 4.4 Created: 02/Mar/21  Updated: 29/Oct/23  Resolved: 13/May/21

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: 4.4.7

Type: Improvement Priority: Major - P3
Reporter: Louis Williams Assignee: Gregory Wlodarek
Resolution: Fixed Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Depends
Problem/Incident
Related
related to SERVER-16049 Replicate capped collection deletes e... Closed
related to SERVER-52892 Perform capped deletes in the same WU... Closed
related to SERVER-63339 Investigate enabling more data consis... Closed
Backwards Compatibility: Fully Compatible
Sprint: Execution Team 2021-05-17
Participants:
Linked BF Score: 181

 Description   

Capped collections perform un-timestamped writes to delete expired documents, but all documents will have had an assigned timestamp when first inserted. This breaks contracts with the storage engine regarding mixed-use timestamps and means that point-in-time reads do not work correctly on capped collections.

As a result, background validation and dbHash will fail with the following errors when reading documents that have just been deleted:

  • DataCorruptionDetected: Erroneous index key found with reference to non-existent record id
  • Index with name X has inconsistencies.

These inconsistencies should be inconsequential because they can only happen when reading documents that have already been deleted.

We already prohibit the use of readConcern: 'snapshot' and multi-document transactions on capped collections for this reason.



 Comments   
Comment by Githook User [ 13/May/21 ]

Author:

{'name': 'Gregory Wlodarek', 'email': 'gregory.wlodarek@mongodb.com', 'username': 'GWlodarek'}

Message: SERVER-54890 Disable background validation and dbHash checks on capped collections
Branch: v4.4
https://github.com/mongodb/mongo/commit/d739233ca231e1da70243086e0edc7a9aac7a772

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