priyen-stripe

add gauges + rejections counter for mse thread usage and limit when the limiting feature is used

4

Currently, when you use the multi stage engine thread limiting feature, (via configs such as below) ``` pinot.server.query.executor.mse.max.execution.threads=1000 pinot.server.query.executor.mse.max.execution.threads.exceed.strategy=ERROR ``` you have no insights, through metrics, what's the current usage...

end to end tracking lag feature removed unintentionally

3

https://github.com/apache/pinot/pull/16783 removed this feature thinking it is not used, but it was a functional feature which we use in stripe https://github.com/apache/pinot/pull/16783#issuecomment-3498367846