StoneDB 子查询优化

摘要:

说明如何优化 exists 的 join 查询优化器的处理

核心函数:

TwoDimensionalJoiner::ChooseJoinAlgorithm

JoinAlgType TwoDimensionalJoiner::ChooseJoinAlgorithm([[maybe_unused]] MultiIndex &mind, Condition &cond) {
  JoinAlgType join_alg = JoinAlgType::JTYPE_GENERAL;

  if (cond[0].IsType_JoinSimple() && cond[0].op == common::Operator::O_EQ) {
    if ((cond.Size() == 1) && !stonedb_sysvar_force_hashjoin)
      join_alg = JoinAlgType::JTYPE_MAP;  // available types checked inside
    else
      join_alg = JoinAlgType::JTYPE_HASH;
  } else {
    if (cond[0].IsType_JoinSimple() &&
        (cond[0].op == common::Operator::O_MORE_EQ || cond[0].op == common::Operator::O_MORE ||
         cond[0].op == common::Operator::O_LESS_EQ || cond[0].op == common::Operator::O_LESS))
      join_alg = JoinAlgType::JTYPE_SORT;
  }
  return join_alg;
}

选择 join 优化器问题分析:

1. 仅判定 join simple 场景，未判断 exists 子句
2. cond [0].IsType_JoinSimple () 如果走入了 else 分支，相当于被执行了两次

ChooseJoinAlgorithm 函数优化:

1. 加入 exists 的判定，以 IsType_JoinSimple 和 == common::Operator:
   标签：JoinAlgType,join,JTYPE,cond,common,StoneDB,Operator,查询,优化
   From： https://www.cnblogs.com/htx666/p/16799211.html