[jira] [Commented] (KAFKA-3753) Metrics for StateStores

["Jeff Klukas (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-3753?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15318521#comment-15318521 ] 

Jeff Klukas commented on KAFKA-3753:
------------------------------------

It's good to know about MeteredKeyValueStore. And holding off on cache-related metrics for the redesign sounds reasonable.

It looks like the KeyValueStore interface does not provide any method related to number of entries (besides calling `all()` and iterating over all values, which doesn't seem reasonable), so there's no way for MeteredKeyValueStore to access the number of entries in the wrapped store. Could we consider adding a `size` method to the KeyValueStore interface?

> Metrics for StateStores
> -----------------------
>
>                 Key: KAFKA-3753
>                 URL: https://issues.apache.org/jira/browse/KAFKA-3753
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Jeff Klukas
>            Assignee: Guozhang Wang
>            Priority: Minor
>              Labels: api
>             Fix For: 0.10.1.0
>
>
> As a developer building a Kafka Streams application, I'd like to have visibility into what's happening with my state stores. How can I know if a particular store is growing large? How can I know if a particular store is frequently needing to hit disk?
> I'm interested to know if there are existing mechanisms for extracting this information or if other people have thoughts on how we might approach this.
> I can't think of a way to provide metrics generically, so each state store implementation would likely need to handle this separately. Given that the default RocksDBStore will likely be the most-used, it would be a first target for adding metrics.
> I'd be interested in knowing the total number of entries in the store, the total size on disk and in memory, rates of gets and puts, and hit/miss ratio for the MemoryLRUCache. Some of these numbers are likely calculable through the RocksDB API, others may simply not be accessible.
> Would there be value to the wider community in having state stores register metrics?



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