[jira] [Created] (KAFKA-5174) RocksDb might stall in environments with 1 core only

["Eno Thereska (JIRA)" <ji...@apache.org>]

Eno Thereska created KAFKA-5174:
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             Summary: RocksDb might stall in environments with 1 core only
                 Key: KAFKA-5174
                 URL: https://issues.apache.org/jira/browse/KAFKA-5174
             Project: Kafka
          Issue Type: Bug
          Components: streams
    Affects Versions: 0.10.2.1
            Reporter: Eno Thereska


- there is a regression in 0.10.2.1 that impacts RocksDb's behaviour (details below for first impact) from this PR: https://github.com/apache/kafka/commit/f9660e16dafb9e1109704bdecb978b7046f0cc6b#diff-046ca566243518c88e007b7499ec9f51

- worst-case impact: streams might not run out-of-box in deployments with 1 core only
- workaround: no new jars needed for the workaround, only a config change that changes a RocksDb parameter, e.g. something like in this PR: https://github.com/confluentinc/examples/pull/117/files


- full fix: add 1 to the current config (i.e., max cpus + 1) in the default settings

The RocksDb code might have a bug itself, since when running with one core
it both sets the number of compaction threads to 1 (https://github.com/facebook/rocksdb/blob/5.0.fb/util/options.cc#L762) AND the maximum number of compactions variable to 0 (https://github.com/facebook/rocksdb/blob/5.0.fb/util/options.cc#L760) which doesn't make much sense. I've sent a message in RocksDb channel.



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