org.apache.drill.exec.store.parquet.columnreaders.BatchReader.java Source code

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Here is the source code for org.apache.drill.exec.store.parquet.columnreaders.BatchReader.java

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/*
 * 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.drill.exec.store.parquet.columnreaders;

import java.io.IOException;
import java.util.ArrayList;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;

import com.google.common.base.Stopwatch;
import com.google.common.collect.Lists;

/**
 * Base strategy for reading a batch of Parquet records.
 */
public abstract class BatchReader {

    protected final ReadState readState;

    public BatchReader(ReadState readState) {
        this.readState = readState;
    }

    public int readBatch() throws Exception {
        ColumnReader<?> firstColumnStatus = readState.getFirstColumnReader();
        long recordsToRead = Math.min(getReadCount(firstColumnStatus), readState.getRecordsToRead());
        int readCount = readRecords(firstColumnStatus, recordsToRead);
        readState.fillNullVectors(readCount);
        return readCount;
    }

    protected abstract long getReadCount(ColumnReader<?> firstColumnStatus);

    protected abstract int readRecords(ColumnReader<?> firstColumnStatus, long recordsToRead) throws Exception;

    protected void readAllFixedFields(long recordsToRead) throws Exception {
        Stopwatch timer = Stopwatch.createStarted();
        if (readState.useAsyncColReader()) {
            readAllFixedFieldsParallel(recordsToRead);
        } else {
            readAllFixedFieldsSerial(recordsToRead);
        }
        readState.parquetReaderStats().timeFixedColumnRead.addAndGet(timer.elapsed(TimeUnit.NANOSECONDS));
    }

    protected void readAllFixedFieldsSerial(long recordsToRead) throws IOException {
        for (ColumnReader<?> crs : readState.getColumnReaders()) {
            crs.processPages(recordsToRead);
        }
    }

    protected void readAllFixedFieldsParallel(long recordsToRead) throws Exception {
        ArrayList<Future<Long>> futures = Lists.newArrayList();
        for (ColumnReader<?> crs : readState.getColumnReaders()) {
            Future<Long> f = crs.processPagesAsync(recordsToRead);
            if (f != null) {
                futures.add(f);
            }
        }
        Exception exception = null;
        for (Future<Long> f : futures) {
            if (exception != null) {
                f.cancel(true);
            } else {
                try {
                    f.get();
                } catch (Exception e) {
                    f.cancel(true);
                    exception = e;
                }
            }
        }
        if (exception != null) {
            throw exception;
        }
    }

    /**
     * Strategy for reading mock records. Mock records appear to occur in the case
     * in which the query has SELECT a, b, but the Parquet file has only c, d.
     * A mock scan reads dummy columns for all records to ensure that the batch
     * contains a record for each Parquet record, but with no data per record.
     * (This explanation is reverse-engineered from the code and may be wrong.
     * Caveat emptor!)
     */

    public static class MockBatchReader extends BatchReader {

        public MockBatchReader(ReadState readState) {
            super(readState);
        }

        @Override
        protected long getReadCount(ColumnReader<?> firstColumnStatus) {
            if (readState.recordsRead() == readState.schema().getGroupRecordCount()) {
                return 0;
            }
            return Math.min(ParquetRecordReader.DEFAULT_RECORDS_TO_READ_IF_VARIABLE_WIDTH,
                    readState.schema().getGroupRecordCount() - readState.recordsRead());
        }

        @Override
        protected int readRecords(ColumnReader<?> firstColumnStatus, long recordsToRead) {
            readState.updateCounts((int) recordsToRead);
            return (int) recordsToRead;
        }
    }

    /**
     * Strategy for reading a record batch when all columns are
     * fixed-width.
     */

    public static class FixedWidthReader extends BatchReader {

        public FixedWidthReader(ReadState readState) {
            super(readState);
        }

        @Override
        protected long getReadCount(ColumnReader<?> firstColumnStatus) {
            return Math.min(readState.schema().getRecordsPerBatch(),
                    firstColumnStatus.columnChunkMetaData.getValueCount() - firstColumnStatus.totalValuesRead);
        }

        @Override
        protected int readRecords(ColumnReader<?> firstColumnStatus, long recordsToRead) throws Exception {
            readAllFixedFields(recordsToRead);
            return firstColumnStatus.getRecordsReadInCurrentPass();
        }
    }

    /**
     * Strategy for reading a record batch when at last one column is
     * variable width.
     */

    public static class VariableWidthReader extends BatchReader {

        public VariableWidthReader(ReadState readState) {
            super(readState);
        }

        @Override
        protected long getReadCount(ColumnReader<?> firstColumnStatus) {
            return ParquetRecordReader.DEFAULT_RECORDS_TO_READ_IF_VARIABLE_WIDTH;
        }

        @Override
        protected int readRecords(ColumnReader<?> firstColumnStatus, long recordsToRead) throws Exception {
            long fixedRecordsToRead = readState.varLengthReader().readFields(recordsToRead);
            readAllFixedFields(fixedRecordsToRead);
            return firstColumnStatus.getRecordsReadInCurrentPass();
        }
    }
}