Add up-to-date javadocs on Translog#syncNeeded

core/src/main/java/org/elasticsearch/index/translog/Translog.java

@@ -541,6 +541,9 @@ public class Translog extends AbstractIndexShardComponent implements IndexShardC
         }
     }
 
+    /**
+     *  Returns <code>true</code> if an fsync is required to ensure durability of the translogs operations or it's metadata.
+     */
     public boolean syncNeeded() {
         try (ReleasableLock lock = readLock.acquire()) {
             return current.syncNeeded();

core/src/main/java/org/elasticsearch/index/translog/TranslogWriter.java

@@ -209,7 +209,8 @@ public class TranslogWriter extends BaseTranslogReader implements Closeable {
     }
 
     /**
-     * returns true if there are buffered ops
+     * Returns <code>true</code> if there are buffered operations that have not been flushed and fsynced to disk or if the latest global
+     * checkpoint has not yet been fsynced
      */
     public boolean syncNeeded() {
         return totalOffset != lastSyncedCheckpoint.offset || globalCheckpointSupplier.getAsLong() != lastSyncedCheckpoint.globalCheckpoint;