vvivekiyer commented on code in PR #9454: URL: https://github.com/apache/pinot/pull/9454#discussion_r980642297
########## pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/index/loader/ForwardIndexHandler.java: ########## @@ -0,0 +1,269 @@ +/** + * 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.index.loader; + +import com.google.common.annotations.VisibleForTesting; +import com.google.common.base.Preconditions; +import java.io.File; +import java.math.BigDecimal; +import java.util.HashMap; +import java.util.HashSet; +import java.util.Map; +import java.util.Set; +import org.apache.commons.io.FileUtils; +import org.apache.pinot.segment.local.segment.readers.PinotSegmentColumnReader; +import org.apache.pinot.segment.spi.ColumnMetadata; +import org.apache.pinot.segment.spi.SegmentMetadata; +import org.apache.pinot.segment.spi.V1Constants; +import org.apache.pinot.segment.spi.compression.ChunkCompressionType; +import org.apache.pinot.segment.spi.creator.IndexCreationContext; +import org.apache.pinot.segment.spi.creator.IndexCreatorProvider; +import org.apache.pinot.segment.spi.creator.SegmentVersion; +import org.apache.pinot.segment.spi.index.creator.ForwardIndexCreator; +import org.apache.pinot.segment.spi.index.reader.ForwardIndexReader; +import org.apache.pinot.segment.spi.store.ColumnIndexType; +import org.apache.pinot.segment.spi.store.SegmentDirectory; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + + +/** + * Helper class used by {@link SegmentPreProcessor} to make changes to forward index and dictionary configs. Note + * that this handler only works if segment versions >= 3.0. The currently supported operations are: + * 1. Change compression on raw SV columns. + * + * TODO: Add support for the following: + * 1. Change compression for raw MV columns + * 2. Enable dictionary + * 3. Disable dictionary + */ +public class ForwardIndexHandler implements IndexHandler { + private static final Logger LOGGER = LoggerFactory.getLogger(ForwardIndexHandler.class); + + private final SegmentMetadata _segmentMetadata; + IndexLoadingConfig _indexLoadingConfig; + + protected enum Operation { + CHANGE_RAW_COMPRESSION_TYPE, + + // TODO: Add other operations like ENABLE_DICTIONARY, DISABLE_DICTIONARY. + } + + public ForwardIndexHandler(SegmentMetadata segmentMetadata, IndexLoadingConfig indexLoadingConfig) { + _segmentMetadata = segmentMetadata; + _indexLoadingConfig = indexLoadingConfig; + } + + @Override + public boolean needUpdateIndices(SegmentDirectory.Reader segmentReader) { + Map<String, Operation> columnOperationMap = computeOperation(segmentReader); + return !columnOperationMap.isEmpty(); + } + + @Override + public void updateIndices(SegmentDirectory.Writer segmentWriter, IndexCreatorProvider indexCreatorProvider) + throws Exception { + Map<String, Operation> columnOperationMap = computeOperation(segmentWriter); + if (columnOperationMap.isEmpty()) { + return; + } + + for (Map.Entry<String, Operation> entry : columnOperationMap.entrySet()) { + String column = entry.getKey(); + Operation operation = entry.getValue(); + + switch (operation) { + case CHANGE_RAW_COMPRESSION_TYPE: + rewriteRawForwardIndex(column, segmentWriter, indexCreatorProvider); + break; + // TODO: Add other operations here. + default: + break; + } + } + } + + @VisibleForTesting + Map<String, Operation> computeOperation(SegmentDirectory.Reader segmentReader) { + Map<String, Operation> columnOperationMap = new HashMap<>(); + + // Works only if the existing segment is V3. + if (_segmentMetadata.getVersion() != SegmentVersion.v3) { + return columnOperationMap; + } + + // From existing column config. + Set<String> existingAllColumns = _segmentMetadata.getAllColumns(); + Set<String> existingDictColumns = + segmentReader.toSegmentDirectory().getColumnsWithIndex(ColumnIndexType.DICTIONARY); + Set<String> existingNoDictColumns = new HashSet<>(); + for (String column : existingAllColumns) { + if (!existingDictColumns.contains(column)) { + existingNoDictColumns.add(column); + } + } + + // From new column config. + Set<String> newNoDictColumns = _indexLoadingConfig.getNoDictionaryColumns(); + + for (String column : existingAllColumns) { + if (existingNoDictColumns.contains(column) && newNoDictColumns.contains(column)) { + // Both existing and new column is RAW forward index encoded. Check if compression needs to be changed. + if (shouldChangeCompressionType(column, segmentReader)) { + columnOperationMap.put(column, Operation.CHANGE_RAW_COMPRESSION_TYPE); + } + } else if (existingNoDictColumns.contains(column) && !newNoDictColumns.contains(column)) { + // TODO: Enable dictionary + } else if (!existingNoDictColumns.contains(column) && newNoDictColumns.contains(column)) { + // TODO: Disable dictionary. + } else { + // No changes necessary. + } + } + + return columnOperationMap; + } + + private boolean shouldChangeCompressionType(String column, SegmentDirectory.Reader segmentReader) { + ColumnMetadata existingColMetadata = _segmentMetadata.getColumnMetadataFor(column); + + // TODO: Remove this MV column limitation. + if (!existingColMetadata.isSingleValue()) { + return false; + } + + // The compression type for an existing segment can only be determined by reading the forward index header. + try { + ForwardIndexReader fwdIndexReader = LoaderUtils.getForwardIndexReader(segmentReader, existingColMetadata); + ChunkCompressionType existingCompressionType = fwdIndexReader.getCompressionType(); + Preconditions.checkState(existingCompressionType != null, + "Existing compressionType cannot be null for raw forward index column=" + column); + + // Get the new compression type. + ChunkCompressionType newCompressionType = null; + Map<String, ChunkCompressionType> newCompressionConfigs = _indexLoadingConfig.getCompressionConfigs(); + if (newCompressionConfigs.containsKey(column)) { + newCompressionType = newCompressionConfigs.get(column); + } + + // Note that default compression type (PASS_THROUGH for metric and LZ4 for dimension) is not considered if the + // compressionType is not explicitly provided in tableConfig. This is to avoid incorrectly rewriting the all + // forward indexes during segmentReload when the default compressionType changes. + if (newCompressionType == null || existingCompressionType == newCompressionType) { + return false; + } + + return true; + } catch (Exception e) { + LOGGER.error("Caught exception while changing compression for column: {}", column, e); + return false; + } + } + + private void rewriteRawForwardIndex(String column, SegmentDirectory.Writer segmentWriter, + IndexCreatorProvider indexCreatorProvider) + throws Exception { + Preconditions.checkState(_segmentMetadata.getVersion() == SegmentVersion.v3); + + ColumnMetadata existingColMetadata = _segmentMetadata.getColumnMetadataFor(column); + File indexDir = _segmentMetadata.getIndexDir(); + String segmentName = _segmentMetadata.getName(); + File inProgress = new File(indexDir, column + ".fwd.inprogress"); + File fwdIndexFile = new File(indexDir, column + V1Constants.Indexes.RAW_SV_FORWARD_INDEX_FILE_EXTENSION); + + if (!inProgress.exists()) { + // Marker file does not exist, which means last run ended normally. + // Create a marker file. + FileUtils.touch(inProgress); + } else { + // Marker file exists, which means last run gets interrupted. + // Remove inverted index if exists. + // For v1 and v2, it's the actual inverted index. For v3, it's the temporary inverted index. Review Comment: Done ########## pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/index/loader/ForwardIndexHandler.java: ########## @@ -0,0 +1,269 @@ +/** + * 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.index.loader; + +import com.google.common.annotations.VisibleForTesting; +import com.google.common.base.Preconditions; +import java.io.File; +import java.math.BigDecimal; +import java.util.HashMap; +import java.util.HashSet; +import java.util.Map; +import java.util.Set; +import org.apache.commons.io.FileUtils; +import org.apache.pinot.segment.local.segment.readers.PinotSegmentColumnReader; +import org.apache.pinot.segment.spi.ColumnMetadata; +import org.apache.pinot.segment.spi.SegmentMetadata; +import org.apache.pinot.segment.spi.V1Constants; +import org.apache.pinot.segment.spi.compression.ChunkCompressionType; +import org.apache.pinot.segment.spi.creator.IndexCreationContext; +import org.apache.pinot.segment.spi.creator.IndexCreatorProvider; +import org.apache.pinot.segment.spi.creator.SegmentVersion; +import org.apache.pinot.segment.spi.index.creator.ForwardIndexCreator; +import org.apache.pinot.segment.spi.index.reader.ForwardIndexReader; +import org.apache.pinot.segment.spi.store.ColumnIndexType; +import org.apache.pinot.segment.spi.store.SegmentDirectory; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + + +/** + * Helper class used by {@link SegmentPreProcessor} to make changes to forward index and dictionary configs. Note + * that this handler only works if segment versions >= 3.0. The currently supported operations are: + * 1. Change compression on raw SV columns. + * + * TODO: Add support for the following: + * 1. Change compression for raw MV columns + * 2. Enable dictionary + * 3. Disable dictionary + */ +public class ForwardIndexHandler implements IndexHandler { + private static final Logger LOGGER = LoggerFactory.getLogger(ForwardIndexHandler.class); + + private final SegmentMetadata _segmentMetadata; + IndexLoadingConfig _indexLoadingConfig; + + protected enum Operation { + CHANGE_RAW_COMPRESSION_TYPE, + + // TODO: Add other operations like ENABLE_DICTIONARY, DISABLE_DICTIONARY. + } + + public ForwardIndexHandler(SegmentMetadata segmentMetadata, IndexLoadingConfig indexLoadingConfig) { + _segmentMetadata = segmentMetadata; + _indexLoadingConfig = indexLoadingConfig; + } + + @Override + public boolean needUpdateIndices(SegmentDirectory.Reader segmentReader) { + Map<String, Operation> columnOperationMap = computeOperation(segmentReader); + return !columnOperationMap.isEmpty(); + } + + @Override + public void updateIndices(SegmentDirectory.Writer segmentWriter, IndexCreatorProvider indexCreatorProvider) + throws Exception { + Map<String, Operation> columnOperationMap = computeOperation(segmentWriter); + if (columnOperationMap.isEmpty()) { + return; + } + + for (Map.Entry<String, Operation> entry : columnOperationMap.entrySet()) { + String column = entry.getKey(); + Operation operation = entry.getValue(); + + switch (operation) { + case CHANGE_RAW_COMPRESSION_TYPE: + rewriteRawForwardIndex(column, segmentWriter, indexCreatorProvider); + break; + // TODO: Add other operations here. + default: + break; + } + } + } + + @VisibleForTesting + Map<String, Operation> computeOperation(SegmentDirectory.Reader segmentReader) { + Map<String, Operation> columnOperationMap = new HashMap<>(); + + // Works only if the existing segment is V3. + if (_segmentMetadata.getVersion() != SegmentVersion.v3) { + return columnOperationMap; + } + + // From existing column config. + Set<String> existingAllColumns = _segmentMetadata.getAllColumns(); + Set<String> existingDictColumns = + segmentReader.toSegmentDirectory().getColumnsWithIndex(ColumnIndexType.DICTIONARY); + Set<String> existingNoDictColumns = new HashSet<>(); + for (String column : existingAllColumns) { + if (!existingDictColumns.contains(column)) { + existingNoDictColumns.add(column); + } + } + + // From new column config. + Set<String> newNoDictColumns = _indexLoadingConfig.getNoDictionaryColumns(); + + for (String column : existingAllColumns) { + if (existingNoDictColumns.contains(column) && newNoDictColumns.contains(column)) { + // Both existing and new column is RAW forward index encoded. Check if compression needs to be changed. + if (shouldChangeCompressionType(column, segmentReader)) { + columnOperationMap.put(column, Operation.CHANGE_RAW_COMPRESSION_TYPE); + } + } else if (existingNoDictColumns.contains(column) && !newNoDictColumns.contains(column)) { + // TODO: Enable dictionary + } else if (!existingNoDictColumns.contains(column) && newNoDictColumns.contains(column)) { + // TODO: Disable dictionary. + } else { + // No changes necessary. + } + } + + return columnOperationMap; + } + + private boolean shouldChangeCompressionType(String column, SegmentDirectory.Reader segmentReader) { + ColumnMetadata existingColMetadata = _segmentMetadata.getColumnMetadataFor(column); + + // TODO: Remove this MV column limitation. + if (!existingColMetadata.isSingleValue()) { + return false; + } + + // The compression type for an existing segment can only be determined by reading the forward index header. + try { + ForwardIndexReader fwdIndexReader = LoaderUtils.getForwardIndexReader(segmentReader, existingColMetadata); + ChunkCompressionType existingCompressionType = fwdIndexReader.getCompressionType(); + Preconditions.checkState(existingCompressionType != null, + "Existing compressionType cannot be null for raw forward index column=" + column); + + // Get the new compression type. + ChunkCompressionType newCompressionType = null; + Map<String, ChunkCompressionType> newCompressionConfigs = _indexLoadingConfig.getCompressionConfigs(); + if (newCompressionConfigs.containsKey(column)) { + newCompressionType = newCompressionConfigs.get(column); + } + + // Note that default compression type (PASS_THROUGH for metric and LZ4 for dimension) is not considered if the + // compressionType is not explicitly provided in tableConfig. This is to avoid incorrectly rewriting the all + // forward indexes during segmentReload when the default compressionType changes. + if (newCompressionType == null || existingCompressionType == newCompressionType) { + return false; + } + + return true; + } catch (Exception e) { + LOGGER.error("Caught exception while changing compression for column: {}", column, e); + return false; + } + } + + private void rewriteRawForwardIndex(String column, SegmentDirectory.Writer segmentWriter, + IndexCreatorProvider indexCreatorProvider) + throws Exception { + Preconditions.checkState(_segmentMetadata.getVersion() == SegmentVersion.v3); + + ColumnMetadata existingColMetadata = _segmentMetadata.getColumnMetadataFor(column); + File indexDir = _segmentMetadata.getIndexDir(); + String segmentName = _segmentMetadata.getName(); + File inProgress = new File(indexDir, column + ".fwd.inprogress"); + File fwdIndexFile = new File(indexDir, column + V1Constants.Indexes.RAW_SV_FORWARD_INDEX_FILE_EXTENSION); + + if (!inProgress.exists()) { + // Marker file does not exist, which means last run ended normally. + // Create a marker file. + FileUtils.touch(inProgress); + } else { + // Marker file exists, which means last run gets interrupted. + // Remove inverted index if exists. + // For v1 and v2, it's the actual inverted index. For v3, it's the temporary inverted index. + FileUtils.deleteQuietly(fwdIndexFile); + } + + LOGGER.info("Creating new forward index for segment={} and column={}", segmentName, column); + + Map<String, ChunkCompressionType> compressionConfigs = _indexLoadingConfig.getCompressionConfigs(); + Preconditions.checkState(compressionConfigs.containsKey(column)); + // At this point, compressionConfigs is guaranteed to contain the column. Review Comment: Done. ########## pinot-segment-local/src/main/java/org/apache/pinot/segment/local/segment/index/loader/ForwardIndexHandler.java: ########## @@ -0,0 +1,269 @@ +/** + * 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.index.loader; + +import com.google.common.annotations.VisibleForTesting; +import com.google.common.base.Preconditions; +import java.io.File; +import java.math.BigDecimal; +import java.util.HashMap; +import java.util.HashSet; +import java.util.Map; +import java.util.Set; +import org.apache.commons.io.FileUtils; +import org.apache.pinot.segment.local.segment.readers.PinotSegmentColumnReader; +import org.apache.pinot.segment.spi.ColumnMetadata; +import org.apache.pinot.segment.spi.SegmentMetadata; +import org.apache.pinot.segment.spi.V1Constants; +import org.apache.pinot.segment.spi.compression.ChunkCompressionType; +import org.apache.pinot.segment.spi.creator.IndexCreationContext; +import org.apache.pinot.segment.spi.creator.IndexCreatorProvider; +import org.apache.pinot.segment.spi.creator.SegmentVersion; +import org.apache.pinot.segment.spi.index.creator.ForwardIndexCreator; +import org.apache.pinot.segment.spi.index.reader.ForwardIndexReader; +import org.apache.pinot.segment.spi.store.ColumnIndexType; +import org.apache.pinot.segment.spi.store.SegmentDirectory; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + + +/** + * Helper class used by {@link SegmentPreProcessor} to make changes to forward index and dictionary configs. Note + * that this handler only works if segment versions >= 3.0. The currently supported operations are: + * 1. Change compression on raw SV columns. + * + * TODO: Add support for the following: + * 1. Change compression for raw MV columns + * 2. Enable dictionary + * 3. Disable dictionary + */ +public class ForwardIndexHandler implements IndexHandler { + private static final Logger LOGGER = LoggerFactory.getLogger(ForwardIndexHandler.class); + + private final SegmentMetadata _segmentMetadata; + IndexLoadingConfig _indexLoadingConfig; + + protected enum Operation { + CHANGE_RAW_COMPRESSION_TYPE, + + // TODO: Add other operations like ENABLE_DICTIONARY, DISABLE_DICTIONARY. + } + + public ForwardIndexHandler(SegmentMetadata segmentMetadata, IndexLoadingConfig indexLoadingConfig) { + _segmentMetadata = segmentMetadata; + _indexLoadingConfig = indexLoadingConfig; + } + + @Override + public boolean needUpdateIndices(SegmentDirectory.Reader segmentReader) { + Map<String, Operation> columnOperationMap = computeOperation(segmentReader); + return !columnOperationMap.isEmpty(); + } + + @Override + public void updateIndices(SegmentDirectory.Writer segmentWriter, IndexCreatorProvider indexCreatorProvider) + throws Exception { + Map<String, Operation> columnOperationMap = computeOperation(segmentWriter); + if (columnOperationMap.isEmpty()) { + return; + } + + for (Map.Entry<String, Operation> entry : columnOperationMap.entrySet()) { + String column = entry.getKey(); + Operation operation = entry.getValue(); + + switch (operation) { + case CHANGE_RAW_COMPRESSION_TYPE: + rewriteRawForwardIndex(column, segmentWriter, indexCreatorProvider); + break; + // TODO: Add other operations here. + default: + break; + } + } + } + + @VisibleForTesting + Map<String, Operation> computeOperation(SegmentDirectory.Reader segmentReader) { + Map<String, Operation> columnOperationMap = new HashMap<>(); + + // Works only if the existing segment is V3. + if (_segmentMetadata.getVersion() != SegmentVersion.v3) { + return columnOperationMap; + } + + // From existing column config. + Set<String> existingAllColumns = _segmentMetadata.getAllColumns(); + Set<String> existingDictColumns = + segmentReader.toSegmentDirectory().getColumnsWithIndex(ColumnIndexType.DICTIONARY); + Set<String> existingNoDictColumns = new HashSet<>(); + for (String column : existingAllColumns) { + if (!existingDictColumns.contains(column)) { + existingNoDictColumns.add(column); + } + } + + // From new column config. + Set<String> newNoDictColumns = _indexLoadingConfig.getNoDictionaryColumns(); + + for (String column : existingAllColumns) { + if (existingNoDictColumns.contains(column) && newNoDictColumns.contains(column)) { + // Both existing and new column is RAW forward index encoded. Check if compression needs to be changed. + if (shouldChangeCompressionType(column, segmentReader)) { + columnOperationMap.put(column, Operation.CHANGE_RAW_COMPRESSION_TYPE); + } + } else if (existingNoDictColumns.contains(column) && !newNoDictColumns.contains(column)) { + // TODO: Enable dictionary + } else if (!existingNoDictColumns.contains(column) && newNoDictColumns.contains(column)) { + // TODO: Disable dictionary. + } else { + // No changes necessary. + } + } + + return columnOperationMap; + } + + private boolean shouldChangeCompressionType(String column, SegmentDirectory.Reader segmentReader) { + ColumnMetadata existingColMetadata = _segmentMetadata.getColumnMetadataFor(column); + + // TODO: Remove this MV column limitation. + if (!existingColMetadata.isSingleValue()) { + return false; + } + + // The compression type for an existing segment can only be determined by reading the forward index header. + try { + ForwardIndexReader fwdIndexReader = LoaderUtils.getForwardIndexReader(segmentReader, existingColMetadata); + ChunkCompressionType existingCompressionType = fwdIndexReader.getCompressionType(); + Preconditions.checkState(existingCompressionType != null, + "Existing compressionType cannot be null for raw forward index column=" + column); + + // Get the new compression type. + ChunkCompressionType newCompressionType = null; + Map<String, ChunkCompressionType> newCompressionConfigs = _indexLoadingConfig.getCompressionConfigs(); + if (newCompressionConfigs.containsKey(column)) { + newCompressionType = newCompressionConfigs.get(column); + } + + // Note that default compression type (PASS_THROUGH for metric and LZ4 for dimension) is not considered if the + // compressionType is not explicitly provided in tableConfig. This is to avoid incorrectly rewriting the all + // forward indexes during segmentReload when the default compressionType changes. + if (newCompressionType == null || existingCompressionType == newCompressionType) { + return false; + } + + return true; + } catch (Exception e) { + LOGGER.error("Caught exception while changing compression for column: {}", column, e); + return false; + } + } + + private void rewriteRawForwardIndex(String column, SegmentDirectory.Writer segmentWriter, + IndexCreatorProvider indexCreatorProvider) + throws Exception { + Preconditions.checkState(_segmentMetadata.getVersion() == SegmentVersion.v3); + + ColumnMetadata existingColMetadata = _segmentMetadata.getColumnMetadataFor(column); + File indexDir = _segmentMetadata.getIndexDir(); + String segmentName = _segmentMetadata.getName(); + File inProgress = new File(indexDir, column + ".fwd.inprogress"); + File fwdIndexFile = new File(indexDir, column + V1Constants.Indexes.RAW_SV_FORWARD_INDEX_FILE_EXTENSION); + + if (!inProgress.exists()) { + // Marker file does not exist, which means last run ended normally. + // Create a marker file. + FileUtils.touch(inProgress); + } else { + // Marker file exists, which means last run gets interrupted. + // Remove inverted index if exists. + // For v1 and v2, it's the actual inverted index. For v3, it's the temporary inverted index. + FileUtils.deleteQuietly(fwdIndexFile); + } + + LOGGER.info("Creating new forward index for segment={} and column={}", segmentName, column); + + Map<String, ChunkCompressionType> compressionConfigs = _indexLoadingConfig.getCompressionConfigs(); + Preconditions.checkState(compressionConfigs.containsKey(column)); + // At this point, compressionConfigs is guaranteed to contain the column. + ChunkCompressionType newCompressionType = compressionConfigs.get(column); + + int numDocs = existingColMetadata.getTotalDocs(); + + try (ForwardIndexReader reader = LoaderUtils.getForwardIndexReader(segmentWriter, existingColMetadata)) { + int lengthOfLongestEntry = reader.getLengthOfLongestEntry(); + Preconditions.checkState(lengthOfLongestEntry >= 0, + "lengthOfLongestEntry cannot be negative. segment=" + segmentName + " column={}" + column); + + IndexCreationContext.Forward context = + IndexCreationContext.builder().withIndexDir(indexDir).withColumnMetadata(existingColMetadata) + .withLengthOfLongestEntry(lengthOfLongestEntry).build() + .forForwardIndex(newCompressionType, _indexLoadingConfig.getColumnProperties()); + + try (ForwardIndexCreator creator = indexCreatorProvider.newForwardIndexCreator(context)) { + PinotSegmentColumnReader columnReader = + new PinotSegmentColumnReader(reader, null, null, existingColMetadata.getMaxNumberOfMultiValues()); + + for (int i = 0; i < numDocs; i++) { + Object val = columnReader.getValue(i); + + // JSON fields are either stored as string or bytes. No special handling is needed. Review Comment: It's not needed here specifically because - as you said we use the storedType. To avoid confusion, I've added a comment for clarification and also used the storedType from reader. This is guaranteed to be either STRING or BYTES for JSON and also easier to understand. Not sure why we have the code in `SegmentColumnarIndexCreator`. As this code also creates a forwardIndex context similar to how IndexHandler does, we should never get JSON type. But it was added recently here https://github.com/apache/pinot/pull/8073. @siddharthteotia any inputs here? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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