HDFS-14693. NameNode should log a warning when EditLog IPC logger's pending size exceeds limit. Contributed by Xudong Cao.

(cherry picked from commit 6ad9a11494c3aea146d7741bf0ad52ce16ad08e6)
(cherry picked from commit 2f2fa3dad6dc62ad0e415fa7892008d47a31ddb4)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/client/IPCLoggerChannel.java

@@ -492,6 +492,10 @@ private synchronized void reserveQueueSpace(int size)
     Preconditions.checkArgument(size >= 0);
     if (queuedEditsSizeBytes + size > queueSizeLimitBytes &&
         queuedEditsSizeBytes > 0) {
+      QuorumJournalManager.LOG.warn("Pending edits to " + IPCLoggerChannel.this
+          + " is going to exceed limit size: " + queueSizeLimitBytes
+          + ", current queued edits size: " + queuedEditsSizeBytes
+          + ", will silently drop " + size + " bytes of edits!");
       throw new LoggerTooFarBehindException();
     }
     queuedEditsSizeBytes += size;