ajantha-bhat commented on a change in pull request #3770:
URL: https://github.com/apache/carbondata/pull/3770#discussion_r434414148



##########
File path: 
sdk/sdk/src/main/java/org/apache/carbondata/sdk/file/PaginationCarbonReader.java
##########
@@ -0,0 +1,302 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.carbondata.sdk.file;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+import org.apache.carbondata.common.annotations.InterfaceAudience;
+import org.apache.carbondata.common.annotations.InterfaceStability;
+import org.apache.carbondata.core.cache.CarbonLRUCache;
+import org.apache.carbondata.core.constants.CarbonCommonConstants;
+import org.apache.carbondata.core.indexstore.BlockletDetailInfo;
+import org.apache.carbondata.hadoop.CarbonInputSplit;
+import org.apache.carbondata.sdk.file.cache.BlockletRows;
+
+import org.apache.hadoop.mapreduce.InputSplit;
+
+/**
+ * CarbonData SDK reader with pagination support
+ */
+@InterfaceAudience.User
+@InterfaceStability.Evolving
+public class PaginationCarbonReader<T> extends CarbonReader<T> {
+  // Splits based the file present in the reader path when the reader is built.
+  private List<InputSplit> allBlockletSplits;
+
+  // Rows till the current splits stored as list.
+  private List<Long> rowCountInSplits;
+
+  // Reader builder used to create the pagination reader, used for building 
split level readers.
+  private CarbonReaderBuilder readerBuilder;
+
+  private boolean isClosed;
+
+  // to store the rows of each blocklet in memory based LRU cache.
+  // key: unique blocklet id
+  // value: BlockletRows
+  private CarbonLRUCache cache =
+      new 
CarbonLRUCache(CarbonCommonConstants.CARBON_MAX_PAGINATION_LRU_CACHE_SIZE_IN_MB,
+          
CarbonCommonConstants.CARBON_MAX_PAGINATION_LRU_CACHE_SIZE_IN_MB_DEFAULT);
+
+  /**
+   * Call {@link #builder(String)} to construct an instance
+   */
+
+  PaginationCarbonReader(List<InputSplit> splits, CarbonReaderBuilder 
readerBuilder) {
+    // Initialize super class with no readers.
+    // Based on the splits identified for pagination query, readers will be 
built for the query.
+    super(null);
+    this.allBlockletSplits = splits;
+    this.readerBuilder = readerBuilder;
+    // prepare the mapping.
+    rowCountInSplits = new ArrayList<>(splits.size());
+    long sum = ((CarbonInputSplit) 
splits.get(0)).getDetailInfo().getRowCount();
+    rowCountInSplits.add(sum);
+    for (int i = 1; i < splits.size(); i++) {
+      // prepare a summation array of row counts in each blocklet,
+      // this is used for pruning with pagination vales.
+      // At current index, it contains sum of rows of all the blocklet from 
previous + current.
+      sum += ((CarbonInputSplit) splits.get(i)).getDetailInfo().getRowCount();
+      rowCountInSplits.add(sum);
+    }
+  }
+
+  /**
+   * Pagination query with from and to range.
+   *
+   * @param fromRowNumber must be greater 0 (as row id starts from 1)
+   *                      and less than equal to toRowNumber
+   * @param toRowNumber must be greater than 0 (as row id starts from 1)
+   *                and greater than equals to fromRowNumber and not outside 
the total rows
+   * @return array of rows between fromRowNumber and toRowNumber (inclusive)
+   * @throws Exception
+   */
+  public Object[] read(long fromRowNumber, long toRowNumber)
+      throws IOException, InterruptedException {
+    if (isClosed) {
+      throw new RuntimeException("Pagination Reader is closed. please build 
again");
+    }
+    if (fromRowNumber < 1) {
+      throw new IllegalArgumentException("from row id:" + fromRowNumber + " is 
less than 1");
+    }
+    if (fromRowNumber > toRowNumber) {
+      throw new IllegalArgumentException(
+          "from row id:" + fromRowNumber + " is greater than to row id:" + 
toRowNumber);
+    }
+    if (toRowNumber > getTotalRows()) {
+      throw new IllegalArgumentException(

Review comment:
       user should know what to pass, getTotalRows() provided for this reason. 
If by mistake he passes wrong value. we should not assume and give till end of 
rows.




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