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Status

Current state: Under Discussion

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

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Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

RocksDB has functionality to collect statistics about its operations to monitor running RocksDB's instances. These statistics enable users to find bottlenecks and to accordingly tune RocksDB. RocksDB's statistics can be accessed programmatically via JNI or RocksDB can be configured to periodically dump them to disk. Although RocksDB provides this functionality, Kafka Streams does currently not expose RocksDB's statistics in its metrics. Hence users need to implement Streams' RocksDBConfigSetter to fetch the statistics. This KIP proposes to expose the subset of the most useful RocksDB's statistics in the metrics of Kafka Streams.  

Public Interfaces

Each exposed metric will have the following tags:

• type = stream-state-metrics,
• thread-id = [thread ID],
• task-id = [task ID]
• rocksdb-state-id = [store ID]

The following metrics will be exposed in the Kafka Streams' metrics

• write-stall-time-(avg|total) [ms]
• bytes-written-rate [bytes/s]
• bytes-written-total [bytes]
• timedout-writes
• bytes-read-rate [bytes/s]
• bytes-read-total [bytes]
• memtable-hit-rate [hits/(hits + misses)] 
• memtable-miss-rate [misses/(hits + misses)] 
• block-cache-bytes-read-rate [bytes/s]
• block-cache-bytes-written-rate [bytes/s]
• block-cache-hit-rate [hits/(hits + misses)]
• block-cache-miss-rate [misses/(hits + misses)]
• bytes-flushed-rate [bytes/s]
• bytes-flushed-total [bytes]
• flush-time-avg [ms]
• flush-time-max [ms]
• flush-time-min [ms]
• bytes-read-compaction-rate [bytes/s]
• bytes-written-compaction-rate [bytes/s]

Briefly list any new interfaces that will be introduced as part of this proposal or any existing interfaces that will be removed or changed. The purpose of this section is to concisely call out the public contract that will come along with this feature.

A public interface is any change to the following:

• Binary log format

• The network protocol and api behavior

• Any class in the public packages under clientsConfiguration, especially client configuration

  • org/apache/kafka/common/serialization

  • org/apache/kafka/common

  • org/apache/kafka/common/errors

  • org/apache/kafka/clients/producer

  • org/apache/kafka/clients/consumer (eventually, once stable)

• Monitoring

• Command line tools and arguments

• Anything else that will likely break existing users in some way when they upgrade

Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

Compatibility, Deprecation, and Migration Plan

• What impact (if any) will there be on existing users?
• If we are changing behavior how will we phase out the older behavior?
• If we need special migration tools, describe them here.
• When will we remove the existing behavior?

Rejected Alternatives

If there are alternative ways of accomplishing the same thing, what were they? The purpose of this section is to motivate why the design is the way it is and not some other way.