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