| /** |
| * 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.hadoop.mapreduce.lib.input; |
| |
| import java.io.IOException; |
| import java.io.InputStream; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| import org.apache.hadoop.conf.Configuration; |
| import org.apache.hadoop.io.Text; |
| import org.apache.hadoop.io.compress.SplitCompressionInputStream; |
| |
| /** |
| * Line reader for compressed splits |
| * |
| * Reading records from a compressed split is tricky, as the |
| * LineRecordReader is using the reported compressed input stream |
| * position directly to determine when a split has ended. In addition the |
| * compressed input stream is usually faking the actual byte position, often |
| * updating it only after the first compressed block after the split is |
| * accessed. |
| * |
| * Depending upon where the last compressed block of the split ends relative |
| * to the record delimiters it can be easy to accidentally drop the last |
| * record or duplicate the last record between this split and the next. |
| * |
| * Split end scenarios: |
| * |
| * 1) Last block of split ends in the middle of a record |
| * Nothing special that needs to be done here, since the compressed input |
| * stream will report a position after the split end once the record |
| * is fully read. The consumer of the next split will discard the |
| * partial record at the start of the split normally, and no data is lost |
| * or duplicated between the splits. |
| * |
| * 2) Last block of split ends in the middle of a delimiter |
| * The line reader will continue to consume bytes into the next block to |
| * locate the end of the delimiter. If a custom delimiter is being used |
| * then the next record must be read by this split or it will be dropped. |
| * The consumer of the next split will not recognize the partial |
| * delimiter at the beginning of its split and will discard it along with |
| * the next record. |
| * |
| * However for the default delimiter processing there is a special case |
| * because CR, LF, and CRLF are all valid record delimiters. If the |
| * block ends with a CR then the reader must peek at the next byte to see |
| * if it is an LF and therefore part of the same record delimiter. |
| * Peeking at the next byte is an access to the next block and triggers |
| * the stream to report the end of the split. There are two cases based |
| * on the next byte: |
| * |
| * A) The next byte is LF |
| * The split needs to end after the current record is returned. The |
| * consumer of the next split will discard the first record, which |
| * is degenerate since LF is itself a delimiter, and start consuming |
| * records after that byte. If the current split tries to read |
| * another record then the record will be duplicated between splits. |
| * |
| * B) The next byte is not LF |
| * The current record will be returned but the stream will report |
| * the split has ended due to the peek into the next block. If the |
| * next record is not read then it will be lost, as the consumer of |
| * the next split will discard it before processing subsequent |
| * records. Therefore the next record beyond the reported split end |
| * must be consumed by this split to avoid data loss. |
| * |
| * 3) Last block of split ends at the beginning of a delimiter |
| * This is equivalent to case 1, as the reader will consume bytes into |
| * the next block and trigger the end of the split. No further records |
| * should be read as the consumer of the next split will discard the |
| * (degenerate) record at the beginning of its split. |
| * |
| * 4) Last block of split ends at the end of a delimiter |
| * Nothing special needs to be done here. The reader will not start |
| * examining the bytes into the next block until the next record is read, |
| * so the stream will not report the end of the split just yet. Once the |
| * next record is read then the next block will be accessed and the |
| * stream will indicate the end of the split. The consumer of the next |
| * split will correctly discard the first record of its split, and no |
| * data is lost or duplicated. |
| * |
| * If the default delimiter is used and the block ends at a CR then this |
| * is treated as case 2 since the reader does not yet know without |
| * looking at subsequent bytes whether the delimiter has ended. |
| * |
| * NOTE: It is assumed that compressed input streams *never* return bytes from |
| * multiple compressed blocks from a single read. Failure to do so will |
| * violate the buffering performed by this class, as it will access |
| * bytes into the next block after the split before returning all of the |
| * records from the previous block. |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Unstable |
| public class CompressedSplitLineReader extends SplitLineReader { |
| |
| SplitCompressionInputStream scin; |
| private boolean usingCRLF; |
| private boolean needAdditionalRecord = false; |
| private boolean finished = false; |
| |
| public CompressedSplitLineReader(SplitCompressionInputStream in, |
| Configuration conf, |
| byte[] recordDelimiterBytes) |
| throws IOException { |
| super(in, conf, recordDelimiterBytes); |
| scin = in; |
| usingCRLF = (recordDelimiterBytes == null); |
| } |
| |
| @Override |
| protected int fillBuffer(InputStream in, byte[] buffer, boolean inDelimiter) |
| throws IOException { |
| int bytesRead = in.read(buffer); |
| |
| // If the split ended in the middle of a record delimiter then we need |
| // to read one additional record, as the consumer of the next split will |
| // not recognize the partial delimiter as a record. |
| // However if using the default delimiter and the next character is a |
| // linefeed then next split will treat it as a delimiter all by itself |
| // and the additional record read should not be performed. |
| if (inDelimiter && bytesRead > 0) { |
| if (usingCRLF) { |
| needAdditionalRecord = (buffer[0] != '\n'); |
| } else { |
| needAdditionalRecord = true; |
| } |
| } |
| return bytesRead; |
| } |
| |
| @Override |
| public int readLine(Text str, int maxLineLength, int maxBytesToConsume) |
| throws IOException { |
| int bytesRead = 0; |
| if (!finished) { |
| // only allow at most one more record to be read after the stream |
| // reports the split ended |
| if (scin.getPos() > scin.getAdjustedEnd()) { |
| finished = true; |
| } |
| |
| bytesRead = super.readLine(str, maxLineLength, maxBytesToConsume); |
| } |
| return bytesRead; |
| } |
| |
| @Override |
| public boolean needAdditionalRecordAfterSplit() { |
| return !finished && needAdditionalRecord; |
| } |
| } |