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Avoid writing empty row group in optimized parquet writer #13248

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raunaqmorarka merged 1 commit into from
Jul 23, 2022
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Avoid writing empty row group in optimized parquet writer #13248

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10 changes: 9 additions & 1 deletion lib/trino-parquet/src/main/java/io/trino/parquet/writer/ParquetWriter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,7 @@

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Verify.verify;
import static com.google.common.collect.ImmutableList.toImmutableList;
import static io.airlift.slice.SizeOf.SIZE_OF_INT;
import static io.airlift.slice.Slices.wrappedBuffer;
Expand Down Expand Up @@ -212,6 +213,14 @@ private void flush()
}
List<BufferData> bufferDataList = builder.build();

if (rows == 0) {
// Avoid writing empty row groups as these are ignored by the reader
verify(
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@sopel39 sopel39 Jul 22, 2022

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Is it possible to write a test?

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@raunaqmorarka raunaqmorarka Jul 23, 2022

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This is going to get tested via #13246 (validation fails because reader ignores empty row group and counts 1 fewer row group than what the writer wrote), that's how I noticed it.

bufferDataList.stream().allMatch(buffer -> buffer.getData().size() == 0),
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"Buffer should be empty when there are no rows");
return;
}

// update stats
long stripeStartOffset = outputStream.longSize();
List<ColumnMetaData> metadatas = bufferDataList.stream()
Expand Down Expand Up @@ -261,7 +270,6 @@ Slice getFooter(List<RowGroup> rowGroups, MessageType messageType)

private void updateRowGroups(List<ColumnMetaData> columnMetaData)
{
// TODO Avoid writing empty row group
long totalBytes = columnMetaData.stream().mapToLong(ColumnMetaData::getTotal_compressed_size).sum();
ImmutableList<org.apache.parquet.format.ColumnChunk> columnChunks = columnMetaData.stream().map(ParquetWriter::toColumnChunk).collect(toImmutableList());
rowGroupBuilder.add(new RowGroup(columnChunks, totalBytes, rows));
Expand Down