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Hello,</div>
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I'm planning to add rate-limited sampling to Java events. It will work similarly to the JVM event jdk.ObjectAllocationSample today. Hopefully, it will make it into JDK 25. I mention this because it may have an impact on JMC. The following events will get a
new setting called "throttle", where a rate can be specified.</div>
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- jdk.SocketRead</div>
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- jdk.SocketWrite</div>
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- jdk.FileRead</div>
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- jdk.FileWrite</div>
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- jdk.JavaExceptionThrow</div>
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The filtering will happen after the threshold setting has been applied. The purpose of the new setting is to have more events enabled by default. The threshold for I/O events today is 20 ms, which is rather high to avoid high CPU usage and buffers being flooded
in pathological applications.</div>
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It may be possible to set the threshold to 0 ms for I/O events when rate-limited sampling is in use in the default configuration, but I'm worried about regressions, so the current plan is to set the threshold to 1 ms and throttle to 300/s. For the profile configuration,
the threshold will be set to 0 ms and the rate increased to 600/s.</div>
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The jdk.JavaErrorThrow event will continue to work as before.</div>
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Long-term, the plan is to sample exceptions per allocation site and remove jdk.JavaErrorThrow. The implementation is more complicated, but I think this will be an improvement for now.</div>
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For JDK 25, the plan is to add control options for method timing and tracing, as part of JEP 520: JFR Method Timing & Tracing. I noticed that the new options will fill the recording wizard, so not all options are visible. The dialog is too small. If we get
throttling for I/O and exceptions into JDK 25, the exception combobox and I/O threshold text box can be removed, so it will be fine without any code changes to JMC.</div>
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If you have questions, please let me know, either here or on the JMC Slack channel.</div>
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Thanks,</div>
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Erik</div>
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