DRIVERS-3274 Send afterClusterTime on writes in causally-consistent sessions.

[matthewdale]

DRIVERS-3274

Update the Causal Consistency spec to require that afterClusterTime is sent on write commands in causally-consistent sessions. Write commands that should send afterClusterTime are:

• insert
• update
• findAndModify
• delete
• bulkWrite
• create
• createIndexes
• drop
• dropDatabase
• dropIndexes

Previously, afterClusterTime was only sent on read commands and the first command in a transaction.

Changes:

• Update the spec prose
• Add two new unified test files for the Causal Consistency spec
• Update the Read Write Concern spec to list write commands that accept readConcern
• Update Transactions and Transactions Convenient API spec tests that explicitly required write commands to omit readConcern.

---

Please complete the following before merging:

• Is the relevant DRIVERS ticket in the PR title?

• Update changelog.
• Test changes in at least one language driver.
• Test these changes against all server versions and topologies (including standalone, replica set, and sharded
  clusters).

[sanych-sun]

LGTM

[dariakp]

@sanych-sun Could you link the C# implementation draft / CI for tests?

[codeowners-service-app]

Assigned Jibola for team dbx-spec-reviewers-unowned because alcaeus is out of office.

[matthewdale]

Here's the Go Driver proof-of-concept implementation: mongodb/mongo-go-driver#2380

[rozza]

Looking good - just a couple of questions.

Also should there be a dropDatabase test in causal-consistency-write-commands.yml?

[sanych-sun]

LGTM + CSharp PR + custom patch with all variants.

[matthewdale]

@rozza There is no "dropDatabase" command supported by the unified test spec. That does means there's a coverage gap for that command in the Causal Consistency spec tests. I'll check if it's worth adding to the unified test spec.

[rozza]

LGTM!

I pushed a date nit fix, rather than dragging out time on a re-review.

The dropDatabase case is unusual with the unified specs - eg it could be added without bumping spec versions, but that could cause issues downstream. So I'm inclined to leave it up to you. The test plan already guides to cover all write scenarios.

[matthewdale]

@rozza I've added a unified spec test for "dropDatabase" and confirmed it works in the Go Driver proof-of-concept, after adding code to handle the "dropDatabase" test operation. I suspect most drivers will have to implement support for "dropDatabase".

[dariakp]

@sanych-sun Could you pull in the new test into the C# implementation to make sure it works as expected?

[sanych-sun]

@dariakp @matthewdale I've re-synced spec tests, all green after adding support for dropDatabase unified operation. Here is the CSharp PR + EG patch.