Jackie-Jiang commented on code in PR #11826: URL: https://github.com/apache/pinot/pull/11826#discussion_r1364618944
########## pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/readers/LazyRow.java: ########## @@ -0,0 +1,83 @@ +/** + * 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.pinot.segment.local.segment.readers; + +import java.io.IOException; +import java.util.HashMap; +import java.util.Set; +import org.apache.pinot.segment.spi.IndexSegment; + + +/** + * A wrapper class to read column values of a row for a given {@link IndexSegment} and docId.<br> + * The advantage of having wrapper over segment and docId is column values are read only when + * {@link LazyRow#getValue(String)} is invoked. + * This is useful to reduce the disk reads incurred due to loading the previous row during merge step. + * There isn't any advantage to have a LazyRow wrap a GenericRow but has been kept for syntactic sugar. + */ +public class LazyRow { + private IndexSegment _segment; Review Comment: Suggest making `_segment` and `_fieldToValueMap` final, and only allow changing `_docId`. The constructor always take a `IndexSegment`, and `init(int docId)` sets the `_docId` and clears the value map ########## pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/readers/LazyRow.java: ########## @@ -0,0 +1,83 @@ +/** + * 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.pinot.segment.local.segment.readers; + +import java.io.IOException; +import java.util.HashMap; +import java.util.Set; +import org.apache.pinot.segment.spi.IndexSegment; + + +/** + * A wrapper class to read column values of a row for a given {@link IndexSegment} and docId.<br> + * The advantage of having wrapper over segment and docId is column values are read only when + * {@link LazyRow#getValue(String)} is invoked. + * This is useful to reduce the disk reads incurred due to loading the previous row during merge step. + * There isn't any advantage to have a LazyRow wrap a GenericRow but has been kept for syntactic sugar. + */ +public class LazyRow { + private IndexSegment _segment; + private int _docId; + private HashMap<String, Object> _fieldToValueMap = new HashMap<>(); + + public LazyRow() { + } + + public LazyRow(IndexSegment segment, int docId) { + _segment = segment; + _docId = docId; + } + + + public void init(IndexSegment segment, int docId) { + this.clear(); + _segment = segment; + _docId = docId; + } + + + public Object getValue(String column) { + if (_segment == null) { + throw new IllegalStateException("Index segment for Lazy row is uninitialized."); + } + return _fieldToValueMap.computeIfAbsent(column, col -> { Review Comment: Currently it will repeatedly read value when the value is `null`. We should enhance it so that even for `null` values, it is only read once ########## pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/readers/LazyRow.java: ########## @@ -0,0 +1,83 @@ +/** + * 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.pinot.segment.local.segment.readers; + +import java.io.IOException; +import java.util.HashMap; +import java.util.Set; +import org.apache.pinot.segment.spi.IndexSegment; + + +/** + * A wrapper class to read column values of a row for a given {@link IndexSegment} and docId.<br> + * The advantage of having wrapper over segment and docId is column values are read only when + * {@link LazyRow#getValue(String)} is invoked. + * This is useful to reduce the disk reads incurred due to loading the previous row during merge step. + * There isn't any advantage to have a LazyRow wrap a GenericRow but has been kept for syntactic sugar. + */ +public class LazyRow { + private IndexSegment _segment; + private int _docId; + private HashMap<String, Object> _fieldToValueMap = new HashMap<>(); + + public LazyRow() { + } + + public LazyRow(IndexSegment segment, int docId) { + _segment = segment; + _docId = docId; + } + + + public void init(IndexSegment segment, int docId) { + this.clear(); + _segment = segment; + _docId = docId; + } + + + public Object getValue(String column) { + if (_segment == null) { + throw new IllegalStateException("Index segment for Lazy row is uninitialized."); + } + return _fieldToValueMap.computeIfAbsent(column, col -> { Review Comment: To solve this problem, we can potentially add another set to track `null` columns, and add an API to read whether the value is `null` ########## pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/readers/LazyRow.java: ########## @@ -0,0 +1,83 @@ +/** + * 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.pinot.segment.local.segment.readers; + +import java.io.IOException; +import java.util.HashMap; +import java.util.Set; +import org.apache.pinot.segment.spi.IndexSegment; + + +/** + * A wrapper class to read column values of a row for a given {@link IndexSegment} and docId.<br> + * The advantage of having wrapper over segment and docId is column values are read only when + * {@link LazyRow#getValue(String)} is invoked. + * This is useful to reduce the disk reads incurred due to loading the previous row during merge step. + * There isn't any advantage to have a LazyRow wrap a GenericRow but has been kept for syntactic sugar. + */ +public class LazyRow { + private IndexSegment _segment; + private int _docId; + private HashMap<String, Object> _fieldToValueMap = new HashMap<>(); + + public LazyRow() { + } + + public LazyRow(IndexSegment segment, int docId) { + _segment = segment; + _docId = docId; + } + + + public void init(IndexSegment segment, int docId) { + this.clear(); + _segment = segment; + _docId = docId; + } + + + public Object getValue(String column) { + if (_segment == null) { Review Comment: This check is no longer needed when we make `_segment` final -- This is an automated message from the Apache Git Service. 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