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[GitHub] [carbondata] ajantha-bhat opened a new pull request #3770: [CARBONDATA-3829] Support pagination in SDK reader

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[GitHub] [carbondata] ajantha-bhat commented on a change in pull request #3770: [CARBONDATA-3829] Support pagination in SDK reader

ajantha-bhat commented on a change in pull request #3770:
URL: https://github.com/apache/carbondata/pull/3770#discussion_r435944901

##########
File path: sdk/sdk/src/main/java/org/apache/carbondata/sdk/file/PaginationCarbonReader.java
##########
@@ -0,0 +1,303 @@
+/*
+ * 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 than 0 (as row id starts from 1)
+ * and less than or equals to toRowNumber
+ * @param toRowNumber must be greater than 0 (as row id starts from 1)
+ * and greater than or equals to fromRowNumber
+ * and should not cross the total rows count
+ * @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(
+ "to row id:" + toRowNumber + " is greater than total rows:" + getTotalRows());
+ }
+ return getRows(fromRowNumber, toRowNumber);
+ }
+
+ /**
+ * Get total rows in the folder or a list of CarbonData files.
+ * It is based on the snapshot of files taken while building the reader.
+ *
+ * @return total rows from all the files in the reader.
+ */
+ public long getTotalRows() {
+ if (isClosed) {
+ throw new RuntimeException("Pagination Reader is closed. please build again");
+ }
+ return rowCountInSplits.get(rowCountInSplits.size() - 1);
+ }
+
+ /**
+ * This interface is for python to call java.
+ * Because python cannot understand java Long object. so send string object.
+ *
+ * Get total rows in the folder or a list of CarbonData files.
+ * It is based on the snapshot of files taken while building the reader.
+ *
+ *
+ * @return total rows from all the files in the reader.
+ */
+ public String getTotalRowsAsString() {
+ if (isClosed) {
+ throw new RuntimeException("Pagination Reader is closed. please build again");
+ }
+ return (rowCountInSplits.get(rowCountInSplits.size() - 1)).toString();
+ }
+
+ private static int findBlockletIndex(List<Long> summationArray, Long key) {
+ // summation array is in sorted order, so can use the binary search.
+ int index = Collections.binarySearch(summationArray, key);
+ if (index < 0) {
+ // when key not found, binary search returns negative index [-1 to -N].
+ // which is the possible place where key can be inserted.
+ // with one shifted position. As 0 is also a valid index.
+ // offset the one index shifted and get absolute value of it.
+ index = Math.abs(index + 1);
+ }
+ return index;
+ }
+
+ private Range getBlockletIndexRange(long fromRowNumber, long toRowNumber) {
+ // find the matching blocklet index range by checking with from and to.
+ int upperBound = findBlockletIndex(rowCountInSplits, toRowNumber);
+ // lower bound cannot be more than upper bound, so work on sub list.
+ int lowerBound = findBlockletIndex(rowCountInSplits.subList(0, upperBound), fromRowNumber);
+ return new Range(lowerBound, upperBound);
+ }
+
+ private Object[] getRows(long fromRowNumber, long toRowNumber)
+ throws IOException, InterruptedException {
+ int rowCount = 0;
+ Object[] rows = new Object[(int)(toRowNumber - fromRowNumber + 1)];
+ // get the matching split index (blocklets) range for the input range.
+ Range blockletIndexRange = getBlockletIndexRange(fromRowNumber, toRowNumber);
+ for (int i = blockletIndexRange.getFrom(); i <= blockletIndexRange.getTo(); i++) {
+ String blockletUniqueId = String.valueOf(i);
+ BlockletRows blockletRows;
+ if (cache.get(blockletUniqueId) != null) {
+ blockletRows = (BlockletRows)cache.get(blockletUniqueId);
+ } else {
+ BlockletDetailInfo detailInfo =
+ ((CarbonInputSplit) allBlockletSplits.get(i)).getDetailInfo();
+ int rowCountInBlocklet = detailInfo.getRowCount();
+ Object[] rowsInBlocklet = new Object[rowCountInBlocklet];
+ // read the rows from the blocklet
+ // TODO: read blocklets in multi-thread if there is a performance requirement.
+ readerBuilder.setInputSplit(allBlockletSplits.get(i));
+ CarbonReader<Object> carbonReader = readerBuilder.build();
+ int count = 0;
+ while (carbonReader.hasNext()) {

Review comment:
should not continue, throw exception to user immediately

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