[jira] [Created] (KAFKA-5477) TransactionalProducer sleeps unnecessarily long during back to back transactions

["Apurva Mehta (JIRA)" <ji...@apache.org>]

Apurva Mehta created KAFKA-5477:
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             Summary: TransactionalProducer sleeps unnecessarily long during back to back transactions
                 Key: KAFKA-5477
                 URL: https://issues.apache.org/jira/browse/KAFKA-5477
             Project: Kafka
          Issue Type: Bug
    Affects Versions: 0.11.0.0
            Reporter: Apurva Mehta
            Assignee: Apurva Mehta


I am running some perf tests for EOS and there is a severe perf impact with our default configs. 

Here is the issue.

# When we do a commit transaction, the producer sends an `EndTxn` request to the coordinator. The coordinator writes the `PrepareCommit` message to the transaction log and then returns the response the client. It writes the transaction markers and the final 'CompleteCommit' message asynchronously. 
# In the mean time, if the client starts another transaction, it will send an `AddPartitions` request on the next `Sender.run` loop. If the markers haven't been written yet, then the coordinator will return a retriable `CONCURRENT_TRANSACTIONS` error to the client.
# The current behavior in the producer is to sleep for `retryBackoffMs` before retrying the request. The current default for this is 100ms. So the producer will sleep for 100ms before sending the `AddPartitions` again. This puts a floor on the latency for transactions.

Ideally, we don't want to sleep the full 100ms  in this particular case, because the retry is 'expected'.

The options are: 
# do nothing, let streams override the retry.backoff.ms in their producer to 10 when EOS is enabled (since they have a HOTFIX patch out anyway).
# Introduce a special 'transactionRetryBackoffMs' non-configurable variable and hard code that to a low value which applies to all transactional requests.
# do nothing and fix it properly in 0.11.0.1 



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