add log msg when event recvr firehose buffer is full (apache#3209)

server/src/main/java/io/druid/segment/realtime/firehose/EventReceiverFirehoseFactory.java

@@ -57,7 +57,6 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Collection;
-import java.util.Date;
 import java.util.List;
 import java.util.Map;
 import java.util.NoSuchElementException;
@@ -147,6 +146,7 @@ public class EventReceiverFirehose implements ChatHandler, Firehose, EventReceiv
     private volatile InputRow nextRow = null;
     private volatile boolean closed = false;
     private final AtomicLong bytesReceived = new AtomicLong(0);
+    private final AtomicLong lastBufferAddFailMsgTime = new AtomicLong(0);
 
     public EventReceiverFirehose(MapInputRowParser parser)
     {
@@ -298,6 +298,13 @@ public void addRows(Iterable<InputRow> rows) throws InterruptedException
         boolean added = false;
         while (!closed && !added) {
           added = buffer.offer(row, 500, TimeUnit.MILLISECONDS);
+          if (!added) {
+            long currTime = System.currentTimeMillis();
+            long lastTime = lastBufferAddFailMsgTime.get();
+            if (currTime - lastTime > 10000 && lastBufferAddFailMsgTime.compareAndSet(lastTime, currTime)) {
+              log.warn("Failed to add event to buffer with current size [%s] . Retrying...", buffer.size());
+            }
+          }
         }
 
         if (!added) {