diff --git a/timeplus-native-jdbc/src/main/java/com/timeplus/data/ColumnLowCardinality.java b/timeplus-native-jdbc/src/main/java/com/timeplus/data/ColumnLowCardinality.java
index 5411115..46b4923 100644
--- a/timeplus-native-jdbc/src/main/java/com/timeplus/data/ColumnLowCardinality.java
+++ b/timeplus-native-jdbc/src/main/java/com/timeplus/data/ColumnLowCardinality.java
@@ -37,20 +37,13 @@ public ColumnLowCardinality(String name, DataTypeLowCardinality type, Object[] v
 
     @Override
     public void write(Object object) throws IOException, SQLException {
-        boolean found = false;
-        for (Object obj : dict) {
-            if (obj != null && obj.equals(object)) {
-                found = true;
-                break;
-            }
-        }
-        if (found) {
-            long value = dict.indexOf(object);
+        long value = dict.indexOf(object);
+        if (value != -1) { 
             indexes.add(value);
         }
         else {
             dict.add(object);
-            long value = dict.indexOf(object);
+            value = dict.indexOf(object);
             indexes.add(value);
         }
     }
@@ -62,15 +55,15 @@ public void flushToSerializer(BinarySerializer serializer, boolean immediate) th
             serializer.writeUTF8StringBinary(type.name());
         }
         if (immediate) {
-            serializer.writeLong(version); //  add version
-            serializer.writeLong(IndexType.UInt64.getValue() | IndexType.HasAdditionalKeysBit.getValue()); //  need to judge the type as additional key
-            serializer.writeLong(dict.size()); //  give dictionary type size
+            /// The data layout: [version][index_type][dictionary][indexes]
+            serializer.writeLong(version);
+            serializer.writeLong(IndexType.UInt64.getValue() | IndexType.HasAdditionalKeysBit.getValue());
+            serializer.writeLong(dict.size());
             for (int i = 0; i < dict.size(); i++) {
                 data.write(dict.get(i));
             }
             data.flushToSerializer(serializer, true);
-
-            serializer.writeLong(indexes.size()); //  give index type size
+            serializer.writeLong(indexes.size());
             for (int i = 0; i < indexes.size(); i++) {
                 serializer.writeLong(indexes.get(i));
             }
diff --git a/timeplus-native-jdbc/src/main/java/com/timeplus/data/type/complex/DataTypeLowCardinality.java b/timeplus-native-jdbc/src/main/java/com/timeplus/data/type/complex/DataTypeLowCardinality.java
index 727eb7a..1848acb 100644
--- a/timeplus-native-jdbc/src/main/java/com/timeplus/data/type/complex/DataTypeLowCardinality.java
+++ b/timeplus-native-jdbc/src/main/java/com/timeplus/data/type/complex/DataTypeLowCardinality.java
@@ -38,6 +38,7 @@ public class DataTypeLowCardinality implements IDataType<Object, Object>  {
     private final String name;
     private final IDataType<?, ?>  nestedDataType;
     private final Long version = 1L;
+    private final Long IndexTypeMask = 0b11111111L;
 
     public DataTypeLowCardinality(String name, IDataType<?, ?>  nestedDataType) {
         this.name = name;
@@ -101,13 +102,13 @@ public void serializeBinaryBulk(Object[] data, BinarySerializer serializer) thro
 
     @Override
     public Object deserializeBinary(BinaryDeserializer deserializer) throws SQLException, IOException {
-        return this.nestedDataType.deserializeBinary(deserializer);
+        return this.getNestedTypes().deserializeBinary(deserializer);
     }
 
     @Override
     public Object[] deserializeBinaryBulk(int rows, BinaryDeserializer deserializer) throws SQLException, IOException {
         if (rows==0) {
-            Object[] data = nestedDataType.deserializeBinaryBulk(rows, deserializer);
+            Object[] data = getNestedTypes().deserializeBinaryBulk(rows, deserializer);
             return data;
         }
         else {
@@ -115,9 +116,9 @@ public Object[] deserializeBinaryBulk(int rows, BinaryDeserializer deserializer)
             if (version != this.version) {
                 throw new SQLException("version error in type low_cardinality");
             }
-            Long index_type = deserializer.readLong() & 0b11111111; //  decide what type it is
+            Long index_type = deserializer.readLong() & IndexTypeMask;
             Long key_nums = deserializer.readLong();
-            Object[] dictionary = nestedDataType.deserializeBinaryBulk(key_nums.intValue(), deserializer);
+            Object[] dictionary = getNestedTypes().deserializeBinaryBulk(key_nums.intValue(), deserializer);
             Long row_nums = deserializer.readLong();
             Object[] data = new Object[rows];
             for (int i = 0; i < row_nums; i++) {