presto-parquet/src/main/java/io/prestosql/parquet/reader/ParquetReader.java/ParquetReader/freeCurrentRowGroupBuffers
class ParquetReader:    private void freeCurrentRowGroupBuffers()
    {
        if (currentRowGroup < 0) {
            return;
        }

        for (int column = 0; column < columns.size(); column++) {
            ChunkReader reader = chunkReaders.get(new ChunkKey(column, currentRowGroup));
            if (reader != null) {
                reader.free();
            }
        }
    }