jackylk commented on a change in pull request #3770:
URL: https://github.com/apache/carbondata/pull/3770#discussion_r433801885
##
File path:
sdk/sdk/src/main/java/org/apache/carbondata/sdk/file/PaginationCarbonReader.java
##
@@ -0,0 +1,296 @@
+/*
+ * 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 extends CarbonReader {
+ // Splits based the file present in the reader path when the reader is built.
+ private List allBlockletSplits;
+
+ // Rows till the current splits stored as list.
+ private List 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 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 from must be greater than 0 and <= to
+ * @param to must be >= from and not outside the total rows
+ * @return array of rows between from and to (inclusive)
+ * @throws Exception
+ */
+ public Object[] read(long from, long to) throws IOException,
InterruptedException {
+if (isClosed) {
+ throw new RuntimeException("Pagination Reader is closed. please build
again");
+}
+if (from < 1) {
+ throw new IllegalArgumentException("from row id:" + from + " is less
than 1");
+}
+if (from > to) {
+ throw new IllegalArgumentException(
+ "from row id:" + from + " is greater than to row id:" + to);
+}
+if (to > getTotalRows()) {
Review comment:
Is parameter starts from 0 or 1? should mention in line 85
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