sparkSQL1.1入门之三:sparkSQL组件之解析
时间:2022-03-14 01:35
上篇在总体上介绍了sparkSQL的运行架构及其基本实现方法(Tree和Rule的配合),也大致介绍了sparkSQL中涉及到的各个概念和组件。本篇将详细地介绍一下关键的一些概念和组件,由于hiveContext继承自sqlContext,关键的概念和组件类似,只不过后者针对hive的特性做了一些修正和重写,所以本篇就只介绍sqlContext的 /*源自 sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala */ object NullPropagation extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
case q: LogicalPlan => q transformExpressionsUp {
case e @ Count(Literal(null, _)) => Cast(Literal(0L), e.dataType)
case e @ Sum(Literal(c, _)) if c == 0 => Cast(Literal(0L), e.dataType)
case e @ Average(Literal(c, _)) if c == 0 => Literal(0.0, e.dataType)
case e @ IsNull(c) if !c.nullable => Literal(false, BooleanType)
case e @ IsNotNull(c) if !c.nullable => Literal(true, BooleanType)
case e @ GetItem(Literal(null, _), _) => Literal(null, e.dataType)
case e @ GetItem(_, Literal(null, _)) => Literal(null, e.dataType)
case e @ GetField(Literal(null, _), _) => Literal(null, e.dataType)
case e @ EqualNullSafe(Literal(null, _), r) => IsNull(r)
case e @ EqualNullSafe(l, Literal(null, _)) => IsNull(l)
......
}
}
}
2:SqlParser
SqlParser的功能就是将SQL语句解析成Unresolved LogicalPlan。现阶段的SqlParser语法解析功能比较简单,支持的语法比较有限。其解析过程中有两个关键组件和一个关键函数:
其次,看看SqlParser的定义,SqlParser继承自类StandardTokenParsers和特质PackratParsers:
其中,PackratParsers:
5:SpankPlan