Apache Hudi 源码分析 JavaClient

JavaClient

Insert,

  @Override
  public List<WriteStatus> insert(List<HoodieRecord<T>> records, String instantTime) {
    HoodieTable<T, List<HoodieRecord<T>>, List<HoodieKey>, List<WriteStatus>> table =
        initTable(WriteOperationType.INSERT, Option.ofNullable(instantTime)); //见下
    table.validateUpsertSchema(); //验证records和table的schema是否匹配，hoodie是写的时候检查schema
    preWrite(instantTime, WriteOperationType.INSERT, table.getMetaClient()); //pre-do，比如从inflight中移除改instant，开启cleaner和archive等服务
    HoodieWriteMetadata<List<WriteStatus>> result = table.insert(context, instantTime, records); //见下
    if (result.getIndexLookupDuration().isPresent()) {
      metrics.updateIndexMetrics(LOOKUP_STR, result.getIndexLookupDuration().get().toMillis());
    }
    return postWrite(result, instantTime, table); //
  }

  

initTable,

注意在改meta的时候会用事务，加全局锁

 /**
   * Instantiates and initializes instance of {@link HoodieTable}, performing crucial bootstrapping
   * operations such as:
   *
   * NOTE: This method is engine-agnostic and SHOULD NOT be overloaded, please check on
   * {@link #doInitTable(HoodieTableMetaClient, Option, boolean)} instead
   *
   * <ul>
   *   <li>Checking whether upgrade/downgrade is required</li>
   *   <li>Bootstrapping Metadata Table (if required)</li>
   *   <li>Initializing metrics contexts</li>
   * </ul>
   */
  protected final HoodieTable initTable(WriteOperationType operationType, Option<String> instantTime, boolean initialMetadataTableIfNecessary) {
    HoodieTableMetaClient metaClient = createMetaClient(true); //读取Meta文件的client

    HoodieTable table;
    Option<HoodieInstant> ownerInstant = Option.empty(); // Instant代表Timeline中一个具体的时间点
    if (instantTime.isPresent()) {
      ownerInstant = Option.of(new HoodieInstant(true, CommitUtils.getCommitActionType(operationType, metaClient.getTableType()), instantTime.get()));
    }
    this.txnManager.beginTransaction(ownerInstant, Option.empty()); //开始事务，调用lockManager.lock，加全局锁
    try {
      tryUpgrade(metaClient, instantTime); //对Table做些准备和恢复工作，比如rollbackFailedWrites，metaClient.reloadActiveTimeline
      table = doInitTable(metaClient, instantTime, initialMetadataTableIfNecessary); //
    } finally {
      this.txnManager.endTransaction(ownerInstant);
    }

doInitTable，生成Table对象

insert

 @Override
  public HoodieWriteMetadata<List<WriteStatus>> insert(HoodieEngineContext context,
                                                       String instantTime,
                                                       List<HoodieRecord<T>> records) {
    return new JavaInsertCommitActionExecutor<>(context, config,
        this, instantTime, records).execute(); //异步线程
  }

JavaInsertCommitActionExecutor

这里调用execute时，会把this作为参数传入

  @Override
  public HoodieWriteMetadata<List<WriteStatus>> execute() {
    return JavaWriteHelper.newInstance().write(instantTime, inputRecords, context, table,
        config.shouldCombineBeforeInsert(), config.getInsertShuffleParallelism(), this, operationType);
  }

JavaWriteHelper

Write

将executor传入继续调用execute的方式，有些tricky

  public HoodieWriteMetadata<O> write(String instantTime,
                                      I inputRecords,
                                      HoodieEngineContext context,
                                      HoodieTable<T, I, K, O> table,
                                      boolean shouldCombine,
                                      int shuffleParallelism,
                                      BaseCommitActionExecutor<T, I, K, O, R> executor,
                                      WriteOperationType operationType) {
    try {
      // De-dupe/merge if needed
      I dedupedRecords =
          combineOnCondition(shouldCombine, inputRecords, shuffleParallelism, table); //消重，merge，见下

      Instant lookupBegin = Instant.now();
      I taggedRecords = dedupedRecords;
      if (table.getIndex().requiresTagging(operationType)) {
        // perform index loop up to get existing location of records
        context.setJobStatus(this.getClass().getSimpleName(), "Tagging");
        taggedRecords = tag(dedupedRecords, context, table); //Tag，即在index中查找location，见下
      }
      Duration indexLookupDuration = Duration.between(lookupBegin, Instant.now()); //记录下查index的耗时

      HoodieWriteMetadata<O> result = executor.execute(taggedRecords); //调用传入的executor继续execute，见下
      result.setIndexLookupDuration(indexLookupDuration);
      return result;

消重，合并该次插入中相同key的record，并进行reduce

  @Override
  public List<HoodieRecord<T>> deduplicateRecords(
      List<HoodieRecord<T>> records, HoodieIndex<?, ?> index, int parallelism) {
    boolean isIndexingGlobal = index.isGlobal();
    Map<Object, List<Pair<Object, HoodieRecord<T>>>> keyedRecords = records.stream().map(record -> { //
      HoodieKey hoodieKey = record.getKey();
      // If index used is global, then records are expected to differ in their partitionPath
      Object key = isIndexingGlobal ? hoodieKey.getRecordKey() : hoodieKey; //如果index是global，那么recordKey就全局唯一的，否则会重复，只能用hoodieKey
      return Pair.of(key, record);
    }).collect(Collectors.groupingBy(Pair::getLeft)); //按Key去group

    return keyedRecords.values().stream().map(x -> x.stream().map(Pair::getRight).reduce((rec1, rec2) -> { //把相同key的record进行reduce
      @SuppressWarnings("unchecked")
      T reducedData = (T) rec1.getData().preCombine(rec2.getData());
      // we cannot allow the user to change the key or partitionPath, since that will affect
      // everything
      // so pick it from one of the records.
      return new HoodieAvroRecord<T>(rec1.getKey(), reducedData);
    }).orElse(null)).filter(Objects::nonNull).collect(Collectors.toList());
  }

tag

  @Override
  protected List<HoodieRecord<T>> tag(List<HoodieRecord<T>> dedupedRecords, HoodieEngineContext context, HoodieTable<T, List<HoodieRecord<T>>, List<HoodieKey>, List<WriteStatus>> table) {
    return HoodieList.getList(
        table.getIndex().tagLocation(HoodieList.of(dedupedRecords), context, table));
  }

tagLocation有多种实现，针对不同的index，看个最简单的HoodieInMemoryHashIndex

  @Override
  public <R> HoodieData<HoodieRecord<R>> tagLocation(
      HoodieData<HoodieRecord<R>> records, HoodieEngineContext context,
      HoodieTable hoodieTable) {
    return records.mapPartitions(hoodieRecordIterator -> {
      List<HoodieRecord<R>> taggedRecords = new ArrayList<>();
      while (hoodieRecordIterator.hasNext()) {
        HoodieRecord<R> record = hoodieRecordIterator.next();
        if (recordLocationMap.containsKey(record.getKey())) { //index中找到该record
          record.unseal(); //
          record.setCurrentLocation(recordLocationMap.get(record.getKey())); //将location set到record中
          record.seal(); //
        }
        taggedRecords.add(record); //记录一下找到location的Record
      }
      return taggedRecords.iterator();
    }, true);
  }

execute

BaseJavaCommitActionExecutor

  @Override
  public HoodieWriteMetadata<List<WriteStatus>> execute(List<HoodieRecord<T>> inputRecords) {
    HoodieWriteMetadata<List<WriteStatus>> result = new HoodieWriteMetadata<>();

    WorkloadProfile workloadProfile = null;
    if (isWorkloadProfileNeeded()) {
      workloadProfile = new WorkloadProfile(buildProfile(inputRecords), table.getIndex().canIndexLogFiles()); //构造Workload profile，见下

    final Partitioner partitioner = getPartitioner(workloadProfile); //获取partitioner，初步分配文件，每个文件对于的record数目
    try {
      saveWorkloadProfileMetadataToInflight(workloadProfile, instantTime); //生成inflight的instant
    } catch (Exception e) {
  
    }
    Map<Integer, List<HoodieRecord<T>>> partitionedRecords = partition(inputRecords, partitioner); //真正的把record分配到各个bucket中去

    List<WriteStatus> writeStatuses = new LinkedList<>();
    partitionedRecords.forEach((partition, records) -> {
      if (WriteOperationType.isChangingRecords(operationType)) {
        handleUpsertPartition(instantTime, partition, records.iterator(), partitioner).forEachRemaining(writeStatuses::addAll); //写文件
      } else {
        handleInsertPartition(instantTime, partition, records.iterator(), partitioner).forEachRemaining(writeStatuses::addAll); //
      }
    });
    updateIndex(writeStatuses, result); //为何index要update两遍
    updateIndexAndCommitIfNeeded(writeStatuses, result); //Commit，见下
    return result;
  }

buildProfile

 protected Pair<HashMap<String, WorkloadStat>, WorkloadStat> buildProfile(List<HoodieRecord<T>> inputRecords) {
    HashMap<String, WorkloadStat> partitionPathStatMap = new HashMap<>(); //按Partiton的WL统计
    WorkloadStat globalStat = new WorkloadStat(); //全局的WL统计，WLStat，insert count和每个fileGroup的update count

    //<PartitionPath,<fileGroupid, record count>>
    Map<Pair<String, Option<HoodieRecordLocation>>, Long> partitionLocationCounts = inputRecords
        .stream()
        .map(record -> Pair.of(
            Pair.of(record.getPartitionPath(), Option.ofNullable(record.getCurrentLocation())), record))
        .collect(Collectors.groupingBy(Pair::getLeft, Collectors.counting()));

    for (Map.Entry<Pair<String, Option<HoodieRecordLocation>>, Long> e : partitionLocationCounts.entrySet()) {
      String partitionPath = e.getKey().getLeft();
      Long count = e.getValue();
      Option<HoodieRecordLocation> locOption = e.getKey().getRight();

      if (!partitionPathStatMap.containsKey(partitionPath)) {
        partitionPathStatMap.put(partitionPath, new WorkloadStat());
      }

      if (locOption.isPresent()) {
        // update
        partitionPathStatMap.get(partitionPath).addUpdates(locOption.get(), count); //
        globalStat.addUpdates(locOption.get(), count); //
      } else {
        // insert
        partitionPathStatMap.get(partitionPath).addInserts(count); //更新Partition级别的WL
        globalStat.addInserts(count); //更新全局WL
      }
    }
    return Pair.of(partitionPathStatMap, globalStat);
  }

getPartitioner

  public JavaUpsertPartitioner(WorkloadProfile workloadProfile, HoodieEngineContext context, HoodieTable table,
                               HoodieWriteConfig config) {
    updateLocationToBucket = new HashMap<>();
    partitionPathToInsertBucketInfos = new HashMap<>();
    bucketInfoMap = new HashMap<>();
    this.workloadProfile = workloadProfile;
    this.table = table;
    this.config = config;
    assignUpdates(workloadProfile); //update本身就是指定了location，assign比较简单，copy
    assignInserts(workloadProfile, context); //insert要考虑现有文件的均衡性，assign复杂些

assignInserts

把所有inserts分配到各个文件，即bucket上

但是这里只是按数目分，粗分

  private void assignInserts(WorkloadProfile profile, HoodieEngineContext context) {
    // for new inserts, compute buckets depending on how many records we have for each partition
    Set<String> partitionPaths = profile.getPartitionPaths();
    long averageRecordSize =
        averageBytesPerRecord(table.getMetaClient().getActiveTimeline().getCommitTimeline().filterCompletedInstants(),
            config); //根据之前的commit的record，估算record的平均size
    LOG.info("AvgRecordSize => " + averageRecordSize);

    Map<String, List<SmallFile>> partitionSmallFilesMap =
        getSmallFilesForPartitions(new ArrayList<String>(partitionPaths), context); //找到每个partition里面的小文件，小文件可以继续insert

    for (String partitionPath : partitionPaths) {
      WorkloadStat pStat = profile.getWorkloadStat(partitionPath); //得到每个partition的input Stat
      WorkloadStat outputWorkloadStats = profile.getOutputPartitionPathStatMap().getOrDefault(partitionPath, new WorkloadStat()); //初始化output stat
      if (pStat.getNumInserts() > 0) {

        List<SmallFile> smallFiles = partitionSmallFilesMap.getOrDefault(partitionPath, new ArrayList<>()); //先得到该partition中的small files
        this.smallFiles.addAll(smallFiles);

        long totalUnassignedInserts = pStat.getNumInserts(); //Stat中的inserts数目作为unassigned
        List<Integer> bucketNumbers = new ArrayList<>(); //bucket概念，
        List<Long> recordsPerBucket = new ArrayList<>(); //这两个list等同于一个map

        // first try packing this into one of the smallFiles，先尽量利用现有的小文件
        for (SmallFile smallFile : smallFiles) {
          long recordsToAppend = Math.min((config.getParquetMaxFileSize() - smallFile.sizeBytes) / averageRecordSize,
              totalUnassignedInserts); //看下这个small file还能放多少条record，直接按MaxFileSize来算
          if (recordsToAppend > 0) {
            // create a new bucket or re-use an existing bucket
            int bucket;
            if (updateLocationToBucket.containsKey(smallFile.location.getFileId())) {
              bucket = updateLocationToBucket.get(smallFile.location.getFileId()); //看下这个file有没有对应的bucket
            } else {
              bucket = addUpdateBucket(partitionPath, smallFile.location.getFileId()); //创建一个bucket，bucketid从0递增
            }
            if (profile.hasOutputWorkLoadStats()) {
              outputWorkloadStats.addInserts(smallFile.location, recordsToAppend);
            }
            bucketNumbers.add(bucket); //更新每个bucket，append多少条records
            recordsPerBucket.add(recordsToAppend);
            totalUnassignedInserts -= recordsToAppend; //
          }
        }

        // if we have anything more, create new insert buckets, like normal
        //如果现有的文件已经放满，创建新的文件
        if (totalUnassignedInserts > 0) {
          long insertRecordsPerBucket = config.getCopyOnWriteInsertSplitSize();
          if (config.shouldAutoTuneInsertSplits()) {
            insertRecordsPerBucket = config.getParquetMaxFileSize() / averageRecordSize;
          }

          int insertBuckets = (int) Math.ceil((1.0 * totalUnassignedInserts) / insertRecordsPerBucket); //算出一共需要新增几个文件，即bucket
         
          for (int b = 0; b < insertBuckets; b++) {
            bucketNumbers.add(totalBuckets); //
            if (b < insertBuckets - 1) { //是不是最后一个bucket，最后一个bucket，record数目不定的
              recordsPerBucket.add(insertRecordsPerBucket);
            } else {
              recordsPerBucket.add(totalUnassignedInserts - (insertBuckets - 1) * insertRecordsPerBucket);
            }
            BucketInfo bucketInfo = new BucketInfo(BucketType.INSERT, FSUtils.createNewFileIdPfx(), partitionPath); //新建bucket
            bucketInfoMap.put(totalBuckets, bucketInfo);
            if (profile.hasOutputWorkLoadStats()) {
              outputWorkloadStats.addInserts(new HoodieRecordLocation(HoodieWriteStat.NULL_COMMIT, bucketInfo.getFileIdPrefix()), recordsPerBucket.get(recordsPerBucket.size() - 1));
            }
            totalBuckets++;
          }
        }

        // Go over all such buckets, and assign weights as per amount of incoming inserts.
        //
        List<InsertBucketCumulativeWeightPair> insertBuckets = new ArrayList<>();
        double currentCumulativeWeight = 0;
        for (int i = 0; i < bucketNumbers.size(); i++) {
          InsertBucket bkt = new InsertBucket();
          bkt.bucketNumber = bucketNumbers.get(i);
          bkt.weight = (1.0 * recordsPerBucket.get(i)) / pStat.getNumInserts(); //weight，bucket被分配的record数目 / 该partition的总插入records数目
          currentCumulativeWeight += bkt.weight; //到当前的bucket，累计weight，最终累计应该是1
          insertBuckets.add(new InsertBucketCumulativeWeightPair(bkt, currentCumulativeWeight)); //记录当前bucket，和累计的weight
        }
        LOG.info("Total insert buckets for partition path " + partitionPath + " => " + insertBuckets);
        partitionPathToInsertBucketInfos.put(partitionPath, insertBuckets); //
      }
      if (profile.hasOutputWorkLoadStats()) {
        profile.updateOutputPartitionPathStatMap(partitionPath, outputWorkloadStats); //
      }
    }
  }

saveWorkloadProfileMetadataToInflight

在timeline上产生一个inflight的instant，如果后面失败，可以直接rollback

  /**
   * Save the workload profile in an intermediate file (here re-using commit files) This is useful when performing
   * rollback for MOR tables. Only updates are recorded in the workload profile metadata since updates to log blocks
   * are unknown across batches Inserts (which are new parquet files) are rolled back based on commit time. // TODO :
   * Create a new WorkloadProfile metadata file instead of using HoodieCommitMetadata
   */
  void saveWorkloadProfileMetadataToInflight(WorkloadProfile profile, String instantTime)
      throws HoodieCommitException {
    try {
      HoodieCommitMetadata metadata = new HoodieCommitMetadata();
      profile.getOutputPartitionPaths().forEach(path -> {
        WorkloadStat partitionStat = profile.getOutputWorkloadStat(path);
        HoodieWriteStat insertStat = new HoodieWriteStat();
        insertStat.setNumInserts(partitionStat.getNumInserts());
        insertStat.setFileId("");
        insertStat.setPrevCommit(HoodieWriteStat.NULL_COMMIT);
        metadata.addWriteStat(path, insertStat);
        Map<String, Pair<String, Long>> updateLocationMap = partitionStat.getUpdateLocationToCount();
        Map<String, Pair<String, Long>> insertLocationMap = partitionStat.getInsertLocationToCount();
        Stream.concat(updateLocationMap.keySet().stream(), insertLocationMap.keySet().stream())
            .distinct()
            .forEach(fileId -> {
              HoodieWriteStat writeStat = new HoodieWriteStat(); //记录每个文件的更新和insert的record数目
              writeStat.setFileId(fileId); //
              Pair<String, Long> updateLocation = updateLocationMap.get(fileId); //
              Pair<String, Long> insertLocation = insertLocationMap.get(fileId);
              // TODO : Write baseCommitTime is possible here ?
              writeStat.setPrevCommit(updateLocation != null ? updateLocation.getKey() : insertLocation.getKey()); //commit版本？
              if (updateLocation != null) {
                writeStat.setNumUpdateWrites(updateLocation.getValue()); //
              }
              if (insertLocation != null) {
                writeStat.setNumInserts(insertLocation.getValue());
              }
              metadata.addWriteStat(path, writeStat); //生成metadata
            });
      });
      metadata.setOperationType(operationType);

      HoodieActiveTimeline activeTimeline = table.getActiveTimeline(); //获取Timeline
      String commitActionType = getCommitActionType();
      HoodieInstant requested = new HoodieInstant(State.REQUESTED, commitActionType, instantTime); //创建Instant
      activeTimeline.transitionRequestedToInflight(requested,
          Option.of(metadata.toJsonString().getBytes(StandardCharsets.UTF_8)),
          config.shouldAllowMultiWriteOnSameInstant()); //将meta转成JSON，写入timeline
    } catch (IOException io) {
      throw new HoodieCommitException("Failed to commit " + instantTime + " unable to save inflight metadata ", io);
    }
  }

partition 

  private Map<Integer, List<HoodieRecord<T>>> partition(List<HoodieRecord<T>> dedupedRecords, Partitioner partitioner) {
    Map<Integer, List<Pair<Pair<HoodieKey, Option<HoodieRecordLocation>>, HoodieRecord<T>>>> partitionedMidRecords = dedupedRecords
        .stream()
        .map(record -> Pair.of(Pair.of(record.getKey(), Option.ofNullable(record.getCurrentLocation())), record)) //<<recordKey, locatiaon> record>
        .collect(Collectors.groupingBy(x -> partitioner.getPartition(x.getLeft()))); //group by bucket, getPartition返回record分配的bucket
    Map<Integer, List<HoodieRecord<T>>> results = new LinkedHashMap<>();
    partitionedMidRecords.forEach((key, value) -> results.put(key, value.stream().map(x -> x.getRight()).collect(Collectors.toList()))); //
    return results;
  }

getPartition

不明白这通操作的意义何在，看着有点唬人

按分配好的bucket，一个个排过去不行？这个基于hash的方式如何保证各个bucket分配的是均匀的？

  @Override
  public int getPartition(Object key) {
    Pair<HoodieKey, Option<HoodieRecordLocation>> keyLocation =
        (Pair<HoodieKey, Option<HoodieRecordLocation>>) key;
    if (keyLocation.getRight().isPresent()) { //如果这个record有location，那就是update，不需要分配
      HoodieRecordLocation location = keyLocation.getRight().get(); //
      return updateLocationToBucket.get(location.getFileId());
    } else {
      String partitionPath = keyLocation.getLeft().getPartitionPath(); //
      List<InsertBucketCumulativeWeightPair> targetBuckets = partitionPathToInsertBucketInfos.get(partitionPath); //获取之前assignInserts生成的累计weight，到每个bucket为止
      // pick the target bucket to use based on the weights.
      final long totalInserts = Math.max(1, workloadProfile.getWorkloadStat(partitionPath).getNumInserts()); //该partition一共的inserts数目
      final long hashOfKey = NumericUtils.getMessageDigestHash("MD5", keyLocation.getLeft().getRecordKey()); //对recordKey取hash值
      final double r = 1.0 * Math.floorMod(hashOfKey, totalInserts) / totalInserts; //hash值对total取模，再除以total，这就得到这个key在total中的位置r

      int index = Collections.binarySearch(targetBuckets, new InsertBucketCumulativeWeightPair(new InsertBucket(), r)); //二分查，这个r在哪个bucket的累计weight范围内

      if (index >= 0) {
        return targetBuckets.get(index).getKey().bucketNumber;
      }

      if ((-1 * index - 1) < targetBuckets.size()) {
        return targetBuckets.get((-1 * index - 1)).getKey().bucketNumber;
      }

      // return first one, by default
      return targetBuckets.get(0).getKey().bucketNumber;
    }
  }

handleUpsertPartition

把数据写入文件

  protected Iterator<List<WriteStatus>> handleUpsertPartition(String instantTime, Integer partition, Iterator recordItr,
                                                              Partitioner partitioner) {
    JavaUpsertPartitioner javaUpsertPartitioner = (JavaUpsertPartitioner) partitioner;
    BucketInfo binfo = javaUpsertPartitioner.getBucketInfo(partition);
    BucketType btype = binfo.bucketType;
    try {
      if (btype.equals(BucketType.INSERT)) {
        return handleInsert(binfo.fileIdPrefix, recordItr); //Insert写入
      } else if (btype.equals(BucketType.UPDATE)) {
        return handleUpdate(binfo.partitionPath, binfo.fileIdPrefix, recordItr); //update更新
      } else {

handleInsert -> JavaLazyInsertIterable

这里做了抽象，producer就是读input，consumer是insertHandler

CopyOnWriteInsertHandler -> HoodieCreateHandle -> HoodieParquetWriter.writeAvroWithMetadata

handleUpdate，逻辑复杂写，需要merge，总体差不多

updateIndexAndCommitIfNeeded

  public void updateIndexAndCommitIfNeeded(List<WriteStatus> writeStatuses, HoodieWriteMetadata result) {
    Instant indexStartTime = Instant.now();
    // Update the index back
    List<WriteStatus> statuses = HoodieList.getList(
        table.getIndex().updateLocation(HoodieList.of(writeStatuses), context, table)); //增加index，record和file的对应关系
    result.setIndexUpdateDuration(Duration.between(indexStartTime, Instant.now())); //
    result.setWriteStatuses(statuses);
    result.setPartitionToReplaceFileIds(getPartitionToReplacedFileIds(result));
    commitOnAutoCommit(result); //commit
  }

commitOnAutoCommit -> autoCommit

  protected void autoCommit(Option<Map<String, String>> extraMetadata, HoodieWriteMetadata<O> result) {
    final Option<HoodieInstant> inflightInstant = Option.of(new HoodieInstant(State.INFLIGHT,
        getCommitActionType(), instantTime));
    this.txnManager.beginTransaction(inflightInstant,
        lastCompletedTxn.isPresent() ? Option.of(lastCompletedTxn.get().getLeft()) : Option.empty()); //开始事务
    try {
      setCommitMetadata(result);
      // reload active timeline so as to get all updates after current transaction have started. hence setting last arg to true.
      TransactionUtils.resolveWriteConflictIfAny(table, this.txnManager.getCurrentTransactionOwner(),
          result.getCommitMetadata(), config, this.txnManager.getLastCompletedTransactionOwner(), true, pendingInflightAndRequestedInstants); //解决写冲突，见下
      commit(extraMetadata, result); //
    } finally {
      this.txnManager.endTransaction(inflightInstant);
    }
  }

resolveWriteConflictIfAny

  public static Option<HoodieCommitMetadata> resolveWriteConflictIfAny(
      final HoodieTable table,
      final Option<HoodieInstant> currentTxnOwnerInstant,
      final Option<HoodieCommitMetadata> thisCommitMetadata,
      final HoodieWriteConfig config,
      Option<HoodieInstant> lastCompletedTxnOwnerInstant,
      boolean reloadActiveTimeline,
      Set<String> pendingInstants) throws HoodieWriteConflictException {
    if (config.getWriteConcurrencyMode().supportsOptimisticConcurrencyControl()) { //是否支持乐观锁
      // deal with pendingInstants
      Stream<HoodieInstant> completedInstantsDuringCurrentWriteOperation = getCompletedInstantsDuringCurrentWriteOperation(table.getMetaClient(), pendingInstants); //找出本次写操作过程中完成的Instants

      ConflictResolutionStrategy resolutionStrategy = config.getWriteConflictResolutionStrategy();
      Stream<HoodieInstant> instantStream = Stream.concat(resolutionStrategy.getCandidateInstants(reloadActiveTimeline
          ? table.getMetaClient().reloadActiveTimeline() : table.getActiveTimeline(), currentTxnOwnerInstant.get(), lastCompletedTxnOwnerInstant),
              completedInstantsDuringCurrentWriteOperation); //加入更多可能冲突的instants
      final ConcurrentOperation thisOperation = new ConcurrentOperation(currentTxnOwnerInstant.get(), thisCommitMetadata.orElse(new HoodieCommitMetadata()));
      instantStream.forEach(instant -> {
        try {
          ConcurrentOperation otherOperation = new ConcurrentOperation(instant, table.getMetaClient());
          if (resolutionStrategy.hasConflict(thisOperation, otherOperation)) { //是否冲突，看两个写操作涉及的文件，是否有交集
            LOG.info("Conflict encountered between current instant = " + thisOperation + " and instant = "
                + otherOperation + ", attempting to resolve it...");
            resolutionStrategy.resolveConflict(table, thisOperation, otherOperation); //发现conflict，抛异常，当前写入失败
          }
        } catch (IOException io) {
          throw new HoodieWriteConflictException("Unable to resolve conflict, if present", io);
        }
      });
      LOG.info("Successfully resolved conflicts, if any");

      return thisOperation.getCommitMetadataOption();
    }
    return thisCommitMetadata;
  }

commit

  protected void commit(Option<Map<String, String>> extraMetadata, HoodieWriteMetadata<List<WriteStatus>> result, List<HoodieWriteStat> writeStats) {
    String actionType = getCommitActionType();
    LOG.info("Committing " + instantTime + ", action Type " + actionType);
    result.setCommitted(true);
    result.setWriteStats(writeStats);
    // Finalize write
    finalizeWrite(instantTime, writeStats, result);
    try {
      HoodieActiveTimeline activeTimeline = table.getActiveTimeline();
      HoodieCommitMetadata metadata = result.getCommitMetadata().get();

      writeTableMetadata(metadata, actionType); //写入meta

      activeTimeline.saveAsComplete(new HoodieInstant(true, getCommitActionType(), instantTime),
          Option.of(metadata.toJsonString().getBytes(StandardCharsets.UTF_8))); //将当前instant的state变成complete
      LOG.info("Committed " + instantTime);
      result.setCommitMetadata(Option.of(metadata));
    } catch (IOException e) {
      throw new HoodieCommitException("Failed to complete commit " + config.getBasePath() + " at time " + instantTime,
          e);
    }
  }