nit: comments and logs from internal feedback

Author: jasonk000

core/src/main/java/com/datastax/oss/driver/internal/core/session/throttling/ConcurrencyLimitingRequestThrottler.java

@@ -61,6 +61,8 @@ public class ConcurrencyLimitingRequestThrottler implements RequestThrottler {
   private final int maxConcurrentRequests;
   private final int maxQueueSize;
   private final AtomicInteger concurrentRequests = new AtomicInteger(0);
+  // CLQ is not O(1) for size(), as it forces a full iteration of the queue. So, we track
+  // the size of the queue explicitly.
   private final Deque<Throttled> queue = new ConcurrentLinkedDeque<>();
   private final AtomicInteger queueSize = new AtomicInteger(0);
   private volatile boolean closed = false;
@@ -93,13 +95,14 @@ public void register(@NonNull Throttled request) {
 
     // If no backlog exists AND we get capacity, we can execute immediately
     if (queueSize.get() == 0) {
+      // Take a claim first, and then check if we are OK to proceed
       int newConcurrent = concurrentRequests.incrementAndGet();
       if (newConcurrent <= maxConcurrentRequests) {
         LOG.trace("[{}] Starting newly registered request", logPrefix);
         request.onThrottleReady(false);
         return;
       } else {
-        // We exceeded the limit, decrement the count and fall through to the queueing logic
+        // We exceeded the limit, decrement the count and fall through to the queuing logic
         concurrentRequests.decrementAndGet();
       }
     }
@@ -121,6 +124,7 @@ public void register(@NonNull Throttled request) {
         }
       }
     } else {
+      LOG.trace("[{}] Rejecting request because of full queue", logPrefix);
       queueSize.decrementAndGet();
       fail(
           request,