Improve S3 grouped deletes

* Move the grouping to outside the main while(true) loop

src/main/java/org/elasticsearch/cloud/aws/blobstore/S3BlobStore.java

@@ -98,18 +98,20 @@ public class S3BlobStore extends AbstractComponent implements BlobStore {
     @Override
     public void delete(BlobPath path) {
         ObjectListing prevListing = null;
+        //From http://docs.amazonwebservices.com/AmazonS3/latest/dev/DeletingMultipleObjectsUsingJava.html
+        //we can do at most 1K objects per delete
+        int objectCount = 0;
+        //We don't know the bucket name until first object listing
+        DeleteObjectsRequest multiObjectDeleteRequest = null;
+        ArrayList<KeyVersion> keys = new ArrayList<KeyVersion>();
         while (true) {
             ObjectListing list;
             if (prevListing != null) {
                 list = client.listNextBatchOfObjects(prevListing);
             } else {
                 list = client.listObjects(bucket, path.buildAsString("/") + "/");
+                multiObjectDeleteRequest = new DeleteObjectsRequest(list.getBucketName());
             }
-            //From http://docs.amazonwebservices.com/AmazonS3/latest/dev/DeletingMultipleObjectsUsingJava.html
-            //we can do at most 1K objects per delete
-            int objectCount = 0;
-            DeleteObjectsRequest multiObjectDeleteRequest = new DeleteObjectsRequest(list.getBucketName());
-            ArrayList<KeyVersion> keys = new ArrayList<KeyVersion>();
             for (S3ObjectSummary summary : list.getObjectSummaries()) {
                 objectCount++;
                 keys.add(new KeyVersion(summary.getKey()));
@@ -122,16 +124,16 @@ public class S3BlobStore extends AbstractComponent implements BlobStore {
                     objectCount = 0;
                 }
             }
-            if (objectCount > 0) {
-                multiObjectDeleteRequest.setKeys(keys);
-                client.deleteObjects(multiObjectDeleteRequest);
-            }
             if (list.isTruncated()) {
                 prevListing = list;
             } else {
                 break;
             }
         }
+        if (objectCount > 0) {
+            multiObjectDeleteRequest.setKeys(keys);
+            client.deleteObjects(multiObjectDeleteRequest);
+        }
     }
 
     @Override