This ticket bans the use of the 'allowSpeculativeMajorityReads' flag for the 'find' command in transactions. This is a very niche use case, and only exists on 4.4, so I'll let the Docs team decide if this is something we need to document for users.

Description of Linked Ticket

Affects 4.4 (observed on 4.4.17-rc0), doesn't seem to affect 4.2 (doesn't reproduce on 4.2.22). Doesn't affect 5.0+ as support for majority read concern is always on.

Behaviour:

• Multi-doc txn with txnNumber:0 and readConcern: { level: 'majority' }

  returns "Given transaction number 0 does not match any in-progress transactions".

  • I believe it should return "Majority read concern is not enabled" instead.
• Multi-doc txn with txnNumber:0 and readConcern: { level: 'majority' }

  and allowSpeculativeMajorityRead: true returns "Given transaction number 0 does not match any in-progress transactions".

  • I believe it should return "Majority read concern is not enabled" instead.
• Multi-doc txn with txnNumber: 1 and readConcern: { level: 'majority' }

  : aborts with "Majority read concern is not enabled"

  • This is expected.
• Multi-doc txn with txn txnNumber:1 and readConcern: { level: 'majority' }

  and allowSpeculativeMajorityRead: true crashes the server.

  • I believe it should return "Majority read concern is not enabled" instead.