【原创】大叔问题定位分享（22）hive同时执行多个insert overwrite table只有1个可以执行

hive 2.1

一 问题

最近有一个场景，要向一个表的多个分区写数据，为了缩短执行时间，采用并发的方式，多个sql同时执行，分别写不同的分区，同时开启动态分区：

set hive.exec.dynamic.partition=true

insert overwrite table test_table partition(dt) select * from test_table_another where dt = 1;

结果发现只有1个sql运行，其他sql都会卡住；
查看hive thrift server线程堆栈发现请求都卡在DbTxnManager上，hive关键配置如下：

hive.support.concurrency=true
hive.txn.manager=org.apache.hadoop.hive.ql.lockmgr.DbTxnManager

配置对应的默认值及注释：

org.apache.hadoop.hive.conf.HiveConf

    HIVE_SUPPORT_CONCURRENCY("hive.support.concurrency", false,
        "Whether Hive supports concurrency control or not. \n" +
        "A ZooKeeper instance must be up and running when using zookeeper Hive lock manager "),
 
    HIVE_TXN_MANAGER("hive.txn.manager",
        "org.apache.hadoop.hive.ql.lockmgr.DummyTxnManager",
        "Set to org.apache.hadoop.hive.ql.lockmgr.DbTxnManager as part of turning on Hive\n" +
        "transactions, which also requires appropriate settings for hive.compactor.initiator.on,\n" +
        "hive.compactor.worker.threads, hive.support.concurrency (true), hive.enforce.bucketing\n" +
        "(true), and hive.exec.dynamic.partition.mode (nonstrict).\n" +
        "The default DummyTxnManager replicates pre-Hive-0.13 behavior and provides\n" +
        "no transactions."),

二 代码分析

hive执行sql的详细过程详见：https://www.cnblogs.com/barneywill/p/10185168.html

hive中执行sql最终都会调用到Driver.run，run会调用runInternal，下面直接看runInternal代码：

org.apache.hadoop.hive.ql.Driver

  private CommandProcessorResponse runInternal(String command, boolean alreadyCompiled)
      throws CommandNeedRetryException {
...
      if (requiresLock()) {
        // a checkpoint to see if the thread is interrupted or not before an expensive operation
        if (isInterrupted()) {
          ret = handleInterruption("at acquiring the lock.");
        } else {
          ret = acquireLocksAndOpenTxn(startTxnImplicitly);
        }
...
 
  private boolean requiresLock() {
    if (!checkConcurrency()) {
      return false;
    }
    // Lock operations themselves don't require the lock.
    if (isExplicitLockOperation()){
      return false;
    }
    if (!HiveConf.getBoolVar(conf, ConfVars.HIVE_LOCK_MAPRED_ONLY)) {
      return true;
    }
    Queue<Task<? extends Serializable>> taskQueue = new LinkedList<Task<? extends Serializable>>();
    taskQueue.addAll(plan.getRootTasks());
    while (taskQueue.peek() != null) {
      Task<? extends Serializable> tsk = taskQueue.remove();
      if (tsk.requireLock()) {
        return true;
      }
...
 
  private boolean checkConcurrency() {
    boolean supportConcurrency = conf.getBoolVar(HiveConf.ConfVars.HIVE_SUPPORT_CONCURRENCY);
    if (!supportConcurrency) {
      LOG.info("Concurrency mode is disabled, not creating a lock manager");
      return false;
    }
    return true;
  }
 
  private int acquireLocksAndOpenTxn(boolean startTxnImplicitly) {
...
      txnMgr.acquireLocks(plan, ctx, userFromUGI);
...

runInternal会调用requiresLock判断是否需要lock，requiresLock有两个判断：

• 调用checkConcurrency，checkConcurrency会检查hive.support.concurrency=true才需要lock;
• 调用Task.requireLock，只有部分task才需要lock；

如果判断需要lock，会调用acquireLocksAndOpenTxn，acquireLocksAndOpenTxn会调用HiveTxnManager.acquireLocks来获取lock；

1）先看那些task需要lock：

org.apache.hadoop.hive.ql.parse.DDLSemanticAnalyzer

  private void analyzeAlterTablePartMergeFiles(ASTNode ast,
      String tableName, HashMap<String, String> partSpec)
      throws SemanticException {
...
      DDLWork ddlWork = new DDLWork(getInputs(), getOutputs(), mergeDesc);
      ddlWork.setNeedLock(true);
...

可见DDL操作需要；

2）再看怎样获取lock：

org.apache.hadoop.hive.ql.lockmgr.DbTxnManager

  public void acquireLocks(QueryPlan plan, Context ctx, String username) throws LockException {
    try {
      acquireLocksWithHeartbeatDelay(plan, ctx, username, 0);
...
 
  void acquireLocksWithHeartbeatDelay(QueryPlan plan, Context ctx, String username, long delay) throws LockException {
    LockState ls = acquireLocks(plan, ctx, username, true);
...
 
  LockState acquireLocks(QueryPlan plan, Context ctx, String username, boolean isBlocking) throws LockException {
...
      switch (output.getType()) {
        case DATABASE:
          compBuilder.setDbName(output.getDatabase().getName());
          break;
 
        case TABLE:
        case DUMMYPARTITION:   // in case of dynamic partitioning lock the table
          t = output.getTable();
          compBuilder.setDbName(t.getDbName());
          compBuilder.setTableName(t.getTableName());
          break;
 
        case PARTITION:
          compBuilder.setPartitionName(output.getPartition().getName());
          t = output.getPartition().getTable();
          compBuilder.setDbName(t.getDbName());
          compBuilder.setTableName(t.getTableName());
          break;
 
        default:
          // This is a file or something we don't hold locks for.
          continue;
      }
...
    LockState lockState = lockMgr.lock(rqstBuilder.build(), queryId, isBlocking, locks);
    ctx.setHiveLocks(locks);
    return lockState;
  }

可见当开启动态分区时，锁的粒度是DbName+TableName，这样就会导致多个sql只有1个sql可以拿到lock，其他sql只能等待；

三 总结

解决问题的方式有几种：

1. 关闭动态分区：set hive.exec.dynamic.partition=false
2. 关闭并发：set hive.support.concurrency=false
3. 关闭事务：set hive.txn.manager=org.apache.hadoop.hive.ql.lockmgr.DummyTxnManager

三者任选其一，推荐第1种，因为在刚才的场景下，不需要动态分区；