gerlowskija opened a new pull request, #2476:
URL: https://github.com/apache/solr/pull/2476

   Tripped soft (i.e. 'warnOnly=true') breakers are logged in a single message 
for each request, whether or not there are any 'hard' breakers that will 
ultimately block the request from proceeding.
   
   
   
   https://issues.apache.org/jira/browse/SOLR-17277
   
   
   # Description
   
   The threshold values used when configuring Circuit Breakers are incredibly 
important. Identifying when load begins to get "dangerous" is tricky: too 
stringent and users will get 429s unnecessarily, too lax and the circuit 
breakers won't be effective at preventing crashes.
   
   It'd be much easier to find and tune these threshold values if Circuit 
Breakers could be enabled in a "warn only" mode, where tripped breakers would 
be logged but not actually "short-circuit" requests.
   
   # Solution
   
   This PR introduces "warnOnly" mode, which can be configured on a 
breaker-by-breaker basis.
   
   Circuit breakers are "hard" by default, but may be put into warn-only mode 
by:
   
   -  adding a `<bool name="warnOnly">true</bool>` setting under the 
`<circuitBreaker/>` tag for collection-level CB's.
   - adding a 'warnonly'-suffixed envvar/sysprop for "global" CB's. (e.g. 
`SOLR_CIRCUITBREAKER_QUERY_MEM_WARNONLY=true`)
   
   # Tests
   
   New test cases in `TestCircuitBreakers` for "warnOnly" mode and to close 
coverage gaps in CB configuration.
   
   # Checklist
   
   Please review the following and check all that apply:
   
   - [x] I have reviewed the guidelines for [How to 
Contribute](https://github.com/apache/solr/blob/main/CONTRIBUTING.md) and my 
code conforms to the standards described there to the best of my ability.
   - [x] I have created a Jira issue and added the issue ID to my pull request 
title.
   - [x] I have given Solr maintainers 
[access](https://help.github.com/en/articles/allowing-changes-to-a-pull-request-branch-created-from-a-fork)
 to contribute to my PR branch. (optional but recommended)
   - [x] I have developed this patch against the `main` branch.
   - [ ] I have run `./gradlew check`.
   - [x] I have added tests for my changes.
   - [ ] I have added documentation for the [Reference 
Guide](https://github.com/apache/solr/tree/main/solr/solr-ref-guide)
   


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