[CASSANDRA-15665] StreamManager should clearly differentiate between "initiator" and "receiver" sessions

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 4.0-beta1, 4.0
• Component/s: Legacy/Streaming and Messaging
• Bug Category: Code
• Severity: Normal
• Complexity: Normal
• Discovered By: Code Inspection
• Platform: All
• Since Version: 4.0-alpha1

Source Control Link

https://github.com/apache/cassandra/commit/ebba613b0b34ea338eed508a3ba6cbb235986fd9

Test and Documentation Plan

PR: https://github.com/apache/cassandra/pull/586
CI: https://circleci.com/workflow-run/947320b4-3c52-4113-91ab-36d622a45e23
 

• Assignee: Zhao Yang
• Reporter: Sergio Bossa

Authors

Zhao Yang

Reviewers

Benjamin Lerer

• Created: 26/Mar/20 12:22
• Updated: 03/Jan/21 17:03
• Resolved: 19/Jun/20 15:34

Description

StreamManager does currently a suboptimal job in differentiating between stream sessions (in form of StreamResultFuture) which have been either initiated or "received", for the following reasons:
1) Naming is IMO confusing: a "receiver" session could actually both send and receive files, so technically an initiator is also a receiver.
2) StreamManager#findSession() assumes we should first looking into "initiator" sessions, then into "receiver" ones: this is a dangerous assumptions, in particular for test environments where the same process could work as both an initiator and a receiver.

I would recommend the following changes:
1) Rename "receiver" with "follower" everywhere the former is used.
2) Introduce a new flag into StreamMessageHeader to signal if the message comes from an initiator or follower session, in order to correctly differentiate and look for sessions in StreamManager.

While my arguments above might seem trivial, I believe they will improve clarity and save from potential bugs/headaches at testing time, and doing such changes now that we're revamping streaming for 4.0 seems the right time.