org.apache.parquet.hadoop.DictionaryPageReader Maven / Gradle / Ivy
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* 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
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* KIND, either express or implied. See the License for the
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*/
package org.apache.parquet.hadoop;
import org.apache.parquet.bytes.BytesInput;
import org.apache.parquet.column.ColumnDescriptor;
import org.apache.parquet.column.page.DictionaryPage;
import org.apache.parquet.column.page.DictionaryPageReadStore;
import org.apache.parquet.hadoop.metadata.BlockMetaData;
import org.apache.parquet.hadoop.metadata.ColumnChunkMetaData;
import org.apache.parquet.io.ParquetDecodingException;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
/**
* A {@link DictionaryPageReadStore} implementation that reads dictionaries from
* an open {@link ParquetFileReader}.
*
* This implementation will delegate dictionary reads to a
* {@link ColumnChunkPageReadStore} to avoid extra reads after a row group has
* been loaded into memory.
*/
class DictionaryPageReader implements DictionaryPageReadStore {
private final ParquetFileReader reader;
private final Map columns;
private final Map> dictionaryPageCache;
private ColumnChunkPageReadStore rowGroup = null;
/**
* Instantiate a new DictionaryPageReader.
*
* @param reader The target ParquetFileReader
* @param block The target BlockMetaData
*
* @throws NullPointerException if {@code reader} or {@code block} is
* {@code null}
*/
DictionaryPageReader(ParquetFileReader reader, BlockMetaData block) {
this.reader = Objects.requireNonNull(reader);
this.columns = new HashMap<>();
this.dictionaryPageCache = new ConcurrentHashMap<>();
for (ColumnChunkMetaData column : block.getColumns()) {
columns.put(column.getPath().toDotString(), column);
}
}
/**
* Sets this reader's row group's page store. When a row group is set, this
* reader will delegate to that row group to return dictionary pages. This
* avoids seeking and re-reading dictionary bytes after this reader's row
* group is loaded into memory.
*
* @param rowGroup a ColumnChunkPageReadStore for this reader's row group
*/
void setRowGroup(ColumnChunkPageReadStore rowGroup) {
this.rowGroup = rowGroup;
}
@Override
public DictionaryPage readDictionaryPage(ColumnDescriptor descriptor) {
if (rowGroup != null) {
// if the row group has already been read, use that dictionary
return rowGroup.readDictionaryPage(descriptor);
}
String dotPath = String.join(".", descriptor.getPath());
ColumnChunkMetaData column = columns.get(dotPath);
if (column == null) {
throw new ParquetDecodingException(
"Failed to load dictionary, unknown column: " + dotPath);
}
return dictionaryPageCache.computeIfAbsent(dotPath, key -> {
try {
final DictionaryPage dict =
column.hasDictionaryPage() ? reader.readDictionary(column) : null;
// Copy the dictionary to ensure it can be reused if it is returned
// more than once. This can happen when a DictionaryFilter has two or
// more predicates for the same column. Cache misses as well.
return (dict != null) ? Optional.of(reusableCopy(dict)) : Optional.empty();
} catch (IOException e) {
throw new ParquetDecodingException("Failed to read dictionary", e);
}
}).orElse(null);
}
private static DictionaryPage reusableCopy(DictionaryPage dict)
throws IOException {
return new DictionaryPage(BytesInput.from(dict.getBytes().toByteArray()),
dict.getDictionarySize(), dict.getEncoding());
}
}