Update Jetty thread pool metrics#18883
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Minor comments – thanks.
docs/operations/metrics.md
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| |`jetty/threadPool/busy`|Number of busy threads that has work to do from the worker queue.|Less than or equal to `threadPoolNumTotalThreads`.| | ||
| |`jetty/threadPool/isLowOnThreads`|A rough indicator of whether number of total workable threads allocated is enough to handle the works in the work queue.|0| | ||
| |`jetty/threadPool/total`|Number of total workable threads allocated. This includes internal threads and threads that are ready to serve requests.|Equals the total number of usable threads in the Jetty thread pool (idle + busy).| | ||
| |`jetty/threadPool/ready`| Number of threads that are ready to serve requests. | Equals the total number of usable threads in the Jetty thread pool to serve requests (idle + busy).| |
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nit: spacing on the markdown |.
docs/operations/metrics.md
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| |`jetty/threadPool/isLowOnThreads`|A rough indicator of whether number of total workable threads allocated is enough to handle the works in the work queue.|0| | ||
| |`jetty/threadPool/total`|Number of total workable threads allocated. This includes internal threads and threads that are ready to serve requests.|Equals the total number of usable threads in the Jetty thread pool (idle + busy).| | ||
| |`jetty/threadPool/ready`| Number of threads that are ready to serve requests. | Equals the total number of usable threads in the Jetty thread pool to serve requests (idle + busy).| | ||
| |`jetty/threadPool/utilized`| Number of threads currently in use by the thread pool to serve requests. | Typically well below ready.| |
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Can we frame this as an inequality?
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Jetty recommends getReadyThreads() and getUtilizedThreads() instead of
getIdleThreads()andgetBusyThreads(). The former (and the new metricsjetty/threadPool/readyandjetty/threadPool/utilized) are intended to capture the portion of the thread pool that is actually available for serving requests (short, transient jobs).Otoh the latter also capture the state of internal system threads that are reserved and/or leased for internal Jetty mechanics.
I noticed on busy servers with sustained query load where the “busy” thread count appeared to be constantly saturated, likely because threads leased for thread pool maintenance were being deprioritized even though "isLowOnThreads" was not 1.
It's also useful to get the utilization rate of the thread pool that's serving requests to understand thread pool usage patterns for different servers:
jetty/threadPool/utilizationRateAlso update the documentation for the new metrics and also fixes up descriptions for some existing Jetty metrics.
Release note
Add new Jetty thread pool metrics to capture request-serving thread statistics:
jetty/threadPool/utilized,jetty/threadPool/readyandjetty/threadPool/utilizationRate.This PR has: