Jackie-Jiang commented on code in PR #18163:
URL: https://github.com/apache/pinot/pull/18163#discussion_r3083197169
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pinot-core/src/main/java/org/apache/pinot/core/accounting/QueryResourceAggregator.java:
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@@ -266,6 +302,60 @@ private void evalTriggers() {
}
}
+ /**
+ * Activates an OOM pause. Query threads calling {@link #waitIfPaused()}
will block until the pause is cleared or the
+ * deadline expires. Also hints the JVM to run garbage collection.
+ */
+ private void activatePause(long timeoutMs) {
+ LOGGER.warn("Activating OOM pause for {}ms to allow garbage collection
before killing queries. "
+ + "Heap used bytes: {}", timeoutMs, _usedBytes);
+ // Write deadline before the flag - volatile ordering guarantees any
thread that reads
+ // _pauseActive == true will also see the updated _pauseDeadlineMs.
+ _pauseDeadlineMs = System.currentTimeMillis() + timeoutMs;
+ _pauseActive = true;
+ // Hint the JVM to run GC while query threads are pausing
+ System.gc();
+ }
+
+ /**
+ * Clears the OOM pause and wakes all blocked query threads.
+ */
+ private void clearPause() {
+ LOGGER.info("Clearing OOM pause. Heap used bytes: {}", _usedBytes);
+ _pauseLock.lock();
+ try {
+ _pauseActive = false;
+ _pauseCondition.signalAll();
+ } finally {
+ _pauseLock.unlock();
+ }
+ }
+
+ /**
+ * Called by query threads at sampling checkpoints. Blocks if an OOM pause
is active. Fast-path: single volatile read
+ * when no pause is active.
+ */
+ void waitIfPaused() {
+ if (!_pauseActive) {
+ return;
+ }
+ _pauseLock.lock();
+ try {
+ while (_pauseActive) {
+ long remaining = _pauseDeadlineMs - System.currentTimeMillis();
+ if (remaining <= 0) {
+ break;
+ }
+ _pauseCondition.await(remaining, TimeUnit.MILLISECONDS);
Review Comment:
It is a little bit risky because thread might wake up before watcher thread
tries to terminate the query, causing higher memory usage
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