cshannon commented on code in PR #3151:
URL: https://github.com/apache/accumulo/pull/3151#discussion_r1064018746
##########
core/src/main/java/org/apache/accumulo/core/file/rfile/RFile.java:
##########
@@ -84,6 +95,107 @@
public class RFile {
+ private static class RFileMemoryProtection implements NotificationListener {
+
+ private static class FreeMemoryUpdater implements Runnable {
+
+ private final ReentrantLock lock = new ReentrantLock();
+ private final AtomicReference<CountDownLatch> latchRef =
+ new AtomicReference<>(new CountDownLatch(1));
+
+ public void update() {
+ lock.lock();
+ try {
+ latchRef.get().countDown();
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ @Override
+ public void run() {
+ try {
+ while (true) {
+ CountDownLatch latch = latchRef.get();
+ // TODO: Could use latch.await(long, TimeUnit) to update free
memory
+ // when GC does not occur. It's probable that memory allocations
+ // will occur without GC happening, depending on the memory pool
+ // sizes.
+ latch.await();
+ // acquiring a lock here so that we don't miss a call to update()
while
+ // we are getting the current free memory
+ lock.lock();
+ try {
+ FREE_MEMORY.set(Runtime.getRuntime().freeMemory());
Review Comment:
```suggestion
// Using only runtime.freeMemory() here would give you memory
that is
// definitely available but may not be the amount of memory
before an
// OME occurs which is really the goal. This is due to the
fact that
// freeMemory() will only return the available memory from the
currently
// allocated memory but the JVM may be able to allocate more
memory if
// the -Xmx parameter is used so the true estimated available
free memory
// is actually (maxMemory - allocatedMemory) where
allocatedMemory is
// (totalMemory - freeMemory).
// See
https://stackoverflow.com/questions/12807797/java-get-available-memory
// for more detailed discussion
final Runtime runtime = Runtime.getRuntime();
long allocatedMemory = runtime.totalMemory() -
runtime.freeMemory();
FREE_MEMORY.set(runtime.maxMemory() - allocatedMemory);
```
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