diff --git a/cool-core/src/main/java/com/nus/cool/core/cohort/storage/CohortRet.java b/cool-core/src/main/java/com/nus/cool/core/cohort/storage/CohortRet.java
index 0983edee..63f7fcf7 100644
--- a/cool-core/src/main/java/com/nus/cool/core/cohort/storage/CohortRet.java
+++ b/cool-core/src/main/java/com/nus/cool/core/cohort/storage/CohortRet.java
@@ -44,6 +44,7 @@ int size() {
 
     void add(String user) {
       if (!added.contains(user)) {
+        added.add(user);
         userSequence.add(user);
       }
     }
diff --git a/cool-core/src/main/java/com/nus/cool/core/io/compression/LZ4JavaCompressor.java b/cool-core/src/main/java/com/nus/cool/core/io/compression/LZ4JavaCompressor.java
index f15ab825..33078341 100644
--- a/cool-core/src/main/java/com/nus/cool/core/io/compression/LZ4JavaCompressor.java
+++ b/cool-core/src/main/java/com/nus/cool/core/io/compression/LZ4JavaCompressor.java
@@ -78,7 +78,6 @@ public CompressorOutput compress(List<? extends FieldValue> src) {
       // compress
       int maxLen = lz4.maxCompressedLength(srcBuf.size()) + HEADACC;
       byte[] compressed = new byte[maxLen];
-      System.out.print(srcBuf.size());
       int zlen = this.lz4.compress(srcBuf.getData(), 0, srcBuf.size(), compressed,
           HEADACC, maxLen - HEADACC);
       ByteBuffer buffer = ByteBuffer.wrap(compressed, 0, HEADACC);