[CASSANDRA-11320] Improve backoff policy for cqlsh COPY FROM

• Type: Improvement
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 3.0.5, 3.5
• Component/s: Legacy/Tools
• Labels: doc-impacting
• Assignee: Stefania Alborghetti
• Reporter: Stefania Alborghetti

Authors

Stefania Alborghetti

Reviewers

Tom Hobbs

• Created: 09/Mar/16 02:39
• Updated: 16/Apr/19 09:30
• Resolved: 01/Apr/16 19:12

Description

Currently we have an exponential back-off policy in COPY FROM that kicks in when timeouts are received. However there are two limitations:

• it does not cover new requests and therefore we may not back-off sufficiently to give time to an overloaded server to recover
• the pause is performed in the receiving thread and therefore we may not process server messages quickly enough

There is a static throttling mechanism in rows per second from feeder to worker processes (the INGESTRATE) but the feeder has no idea of the load of each worker process. However it's easy to keep track of how many chunks a worker process has yet to read by introducing a bounded semaphore.

The idea is to move the back-off pauses to the worker processes main thread so as to include all messages, new and retries, not just the retries that timed out. The worker process will not read new chunks during the back-off pauses, and the feeder process can then look at the number of pending chunks before sending new chunks to a worker process.

aholmber, aweisberg what do you think?