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From "Stefania (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-11320) Improve backoff policy for cqlsh COPY FROM
Date Wed, 09 Mar 2016 02:39:40 GMT
Stefania created CASSANDRA-11320:
------------------------------------

             Summary: Improve backoff policy for cqlsh COPY FROM
                 Key: CASSANDRA-11320
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11320
             Project: Cassandra
          Issue Type: Improvement
          Components: Tools
            Reporter: Stefania
            Assignee: Stefania
             Fix For: 3.x


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?  



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