[CASSANDRA-9429] Revert CASSANDRA-7807 (tracing completion client notifications)

• Type: Bug
• Status: Resolved
• Priority: Low
• Resolution: Fixed
• Fix Version/s: 2.2.0 rc1
• Severity: Low
• Assignee: Robert Stupp
• Reporter: Adam Holmberg

Authors

Robert Stupp

Reviewers

Aleksey Yeschenko

• Created: 19/May/15 17:50
• Updated: 16/Apr/19 09:31
• Resolved: 20/May/15 06:50

Description

Follow-on to CASSANDRA-7807, where I opened a discussion without realizing the version was released:

I know I'm late to this ticket, but as I began to integrate this feature for the Python driver, I developed some reservations about its usefulness. I understand the original intent to avoid polling and eventually simplify trace handling. However, it introduces some complexity supporting multiple protocol versions, and I'm not sure it will even avoid the need for polling, due to replication lag.
Here are some of the things required to take advantage:

• Extra registration overhead per connection, or dynamically register on first trace
• Extra book-keeping – trace ID per connection
• New modes of failure (polling is resilient as the cluster)
• Event may arrive before trace data is replicated
• Drivers must still implement polling following event, and for lesser protocol versions

Given the above, I'm not sure it's worth it to implement to save a few polling round-trips, especially when it's only client-initiated traces (which will typically not be in a hot path).

I'm open to discussion on the matter.

Issue Links

• supercedes: CASSANDRA-7807 Push notification when tracing completes for an operation
• supercedes: CASSANDRA-9433 TraceCompleteTest.testTraceComplete is failing infrequently
• links to: Git branch