The jdk.ThreadDump event is currently written when a chunk begins and ends (everyChunk), but when it is written at the beginning, it may trigger another rotation within 1 second. This can cause other relevant data to be flushed out very quickly, e.g. 15 seconds if using the default max size of 250 MB.

Reproducer:

$ java Reproducer 1400 300 20

import java.util.concurrent.Semaphore;
import jdk.jfr.Configuration;
import jdk.jfr.Recording;

public class Reproducer {
    public static void main(String[] args) throws Exception {
        int threadCount = Integer.parseInt(args[0]);
        int stackDepth = Integer.parseInt(args[1]);
        int sleepTime = Integer.parseInt(args[2]);
        Semaphore semaphore = new Semaphore(0);
        for (int i = 0; i < threadCount; i++) {
            Thread t = new Thread(() -> stack(stackDepth, semaphore));
            t.setDaemon(true);
            t.start();
        }
        semaphore.acquire(threadCount);
        Configuration c = Configuration.getConfiguration("default");
        try (Recording r = new Recording(c)) {
            r.start();
            Thread.sleep(sleepTime * 1000);
        }
    }

    static void stack(int depth, Semaphore semaphore) {
        if (depth > 0) {
            stack(depth - 1, semaphore);
        }
        if (depth == 0) {
            semaphore.release();
            try {
                Thread.sleep(Long.MAX_VALUE);
            } catch (InterruptedException ignored) {}
        }
    }
}

Short-term, we could change the implementation so that jdk.ThreadDump and jdk.ClassLoaderStatistics are only emitted when a recording starts and a chunk ends. Such a change may be suitable for backporting.

Longer-term, we might want to address this in a more generic way so that it cannot occur with other events as well, including user-defined ones. Three alternatives:

1) Redefine "everyChunk" so that it only emits when a recording starts and when a chunk ends.
2) Create a new keyword, e.g. "rotation", with the same semantics as option 1, but keep "everyChunk" as is.
3) Broaden the setting so it can accept a combination of recording- or chunk-specific settings.

Regardless of approach, the new semantics must support cases where two recordings are in use at the same time with different settings.