[jira] [Commented] (CASSANDRA-17062) Expose Auth Caches metrics

["Aleksei Zotov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-17062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17481851#comment-17481851 ] 

Aleksei Zotov commented on CASSANDRA-17062:
-------------------------------------------

Thanks for the feedback [~samt]!

>  I don't see any harm in the all cache metrics including a {{{}weightedSize{}}}, for unweighted caches this is just equal to {{size}} and simply isn't included in the VT/nodetool output.

I think MBeans are also a part of the presentation layer (not only VT and nodetool) since they are exposed to end users. I find "conditional MBean attributes" (meaning they can be populated conditionally or treated differently) to be very confusing. So I think having different entities for different MBeans (`CacheMetrics` and `UnweightedCacheMetrics`) is smth clearer to the end user. WDYT?

I've intentionally not brought `CacheSize`/`UnweightedCacheSize` into this discussion. Let's come to a consensus on Mbeans at first.

> The only real difference between the types at this level is the units of size/capacity, which are not explicit and only referenced in comments.

Ideally I'd make a bigger refactoring with more expressive naming, etc, but I do not feel it is justifiable to make a bigger change for such a simple ticket. Especially I'm concerned with renaming old classes (possible conflicts resolution going further) while keeping MBeans compatible (which is possible though).

> As implemented, the mechanism of tracking hits/misses isn't correct. 

Great catch! I was referencing to the logic implemented in `InstrumentingCache`. However, it turned out that it uses uses `getIfPresent` instead of `get` method, so does not experience the problem you described. Your fix seems to be  necessary and correct!

> Expose Auth Caches metrics
> --------------------------
>
>                 Key: CASSANDRA-17062
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-17062
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Feature/Virtual Tables, Observability/Metrics, Tool/nodetool
>            Reporter: Aleksei Zotov
>            Assignee: Aleksei Zotov
>            Priority: Normal
>             Fix For: 4.x
>
>
> Unlike to other caches (row, key, counter), Auth Caches lack some monitoring capabilities. Here are a few particular changes to get this inequity fixed:
>  # Add auth caches to _system_views.caches_ VT
>  # Expose auth caches metrics via JMX
>  # Add auth caches details to _nodetool info_
>  



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