第三篇：Spark SQL Catalyst源码分析之Analyzer

/** Spark SQL源码分析系列文章*/

    前面几篇文章讲解了Spark SQL的核心执行流程和Spark SQL的Catalyst框架的Sql Parser是怎样接受用户输入sql，经过解析生成Unresolved Logical Plan的。我们记得Spark SQL的执行流程中另一个核心的组件式Analyzer，本文将会介绍Analyzer在Spark SQL里起到了什么作用。

    Analyzer位于Catalyst的analysis package下，主要职责是将Sql Parser 未能Resolved的Logical Plan 给Resolved掉。

    

一、Analyzer构造

    Analyzer会使用Catalog和FunctionRegistry将UnresolvedAttribute和UnresolvedRelation转换为catalyst里全类型的对象。

    Analyzer里面有fixedPoint对象，一个Seq[Batch].

class Analyzer(catalog: Catalog, registry: FunctionRegistry, caseSensitive: Boolean)
  extends RuleExecutor[LogicalPlan] with HiveTypeCoercion {

  // TODO: pass this in as a parameter.
  val fixedPoint = FixedPoint(100)

  val batches: Seq[Batch] = Seq(
    Batch("MultiInstanceRelations", Once,
      NewRelationInstances),
    Batch("CaseInsensitiveAttributeReferences", Once,
      (if (caseSensitive) Nil else LowercaseAttributeReferences :: Nil) : _*),
    Batch("Resolution", fixedPoint,
      ResolveReferences ::
      ResolveRelations ::
      NewRelationInstances ::
      ImplicitGenerate ::
      StarExpansion ::
      ResolveFunctions ::
      GlobalAggregates ::
      typeCoercionRules :_*),
    Batch("AnalysisOperators", fixedPoint,
      EliminateAnalysisOperators)
  )

    Analyzer里的一些对象解释：

    FixedPoint：相当于迭代次数的上限。

/** A strategy that runs until fix point or maxIterations times, whichever comes first. */
case class FixedPoint(maxIterations: Int) extends Strategy

    Batch: 批次，这个对象是由一系列Rule组成的，采用一个策略（策略其实是迭代几次的别名吧，eg：Once）

/** A batch of rules. */，
protected case class Batch(name: String, strategy: Strategy, rules: Rule[TreeType]*)

   Rule：理解为一种规则，这种规则会应用到Logical Plan 从而将UnResolved 转变为Resolved

abstract class Rule[TreeType <: TreeNode[_]] extends Logging {

  /** Name for this rule, automatically inferred based on class name. */
  val ruleName: String = {
    val className = getClass.getName
    if (className endsWith "$") className.dropRight(1) else className
  }

  def apply(plan: TreeType): TreeType
}

   Strategy：最大的执行次数，如果执行次数在最大迭代次数之前就达到了fix point，策略就会停止，不再应用了。

/**
 * An execution strategy for rules that indicates the maximum number of executions. If the
 * execution reaches fix point (i.e. converge) before maxIterations, it will stop.
 */
abstract class Strategy { def maxIterations: Int }

   Analyzer解析主要是根据这些Batch里面定义的策略和Rule来对Unresolved的逻辑计划进行解析的。

   这里Analyzer类本身并没有定义执行的方法，而是要从它的父类RuleExecutor[LogicalPlan]寻找，Analyzer也实现了HiveTypeCosercion，这个类是参考Hive的类型自动兼容转换的原理。如图：

    

    RuleExecutor：执行Rule的执行环境，它会将包含了一系列的Rule的Batch进行执行，这个过程都是串行的。

    具体的执行方法定义在apply里：

    可以看到这里是一个while循环，每个batch下的rules都对当前的plan进行作用，这个过程是迭代的，直到达到Fix Point或者最大迭代次数。

def apply(plan: TreeType): TreeType = {
   var curPlan = plan

   batches.foreach { batch =>
     val batchStartPlan = curPlan
     var iteration = 1
     var lastPlan = curPlan
     var continue = true

     // Run until fix point (or the max number of iterations as specified in the strategy.
     while (continue) {
       curPlan = batch.rules.foldLeft(curPlan) {
         case (plan, rule) =>
           val result = rule(plan) //这里将调用各个不同Rule的apply方法，将UnResolved Relations，Attrubute和Function进行Resolve
           if (!result.fastEquals(plan)) {
             logger.trace(
               s"""
                 |=== Applying Rule ${rule.ruleName} ===
                 |${sideBySide(plan.treeString, result.treeString).mkString("
")}
               """.stripMargin)
           }

           result //返回作用后的result plan
       }
       iteration += 1
       if (iteration > batch.strategy.maxIterations) { //如果迭代次数已经大于该策略的最大迭代次数，就停止循环
         logger.info(s"Max iterations ($iteration) reached for batch ${batch.name}")
         continue = false
       }

       if (curPlan.fastEquals(lastPlan)) { //如果在多次迭代中不再变化，因为plan有个unique id，就停止循环。
         logger.trace(s"Fixed point reached for batch ${batch.name} after $iteration iterations.")
         continue = false
       }
       lastPlan = curPlan
     }

     if (!batchStartPlan.fastEquals(curPlan)) {
       logger.debug(
         s"""
         |=== Result of Batch ${batch.name} ===
         |${sideBySide(plan.treeString, curPlan.treeString).mkString("
")}
       """.stripMargin)
     } else {
       logger.trace(s"Batch ${batch.name} has no effect.")
     }
   }

   curPlan //返回Resolved的Logical Plan
 }

二、Rules介绍

    目前Spark SQL 1.0.0的Rule都定义在了Analyzer.scala的内部类。

    在batches里面定义了4个Batch。

    MultiInstanceRelations、CaseInsensitiveAttributeReferences、Resolution、AnalysisOperators 四个。

    这4个Batch是将不同的Rule进行归类，每种类别采用不同的策略来进行Resolve。

    

2.1、MultiInstanceRelation 

如果一个实例在Logical Plan里出现了多次，则会应用NewRelationInstances这儿Rule

Batch("MultiInstanceRelations", Once,
     NewRelationInstances)

trait MultiInstanceRelation {
  def newInstance: this.type
}

object NewRelationInstances extends Rule[LogicalPlan] {
  def apply(plan: LogicalPlan): LogicalPlan = {
    val localRelations = plan collect { case l: MultiInstanceRelation => l} //将logical plan应用partial function得到所有MultiInstanceRelation的plan的集合
    val multiAppearance = localRelations
      .groupBy(identity[MultiInstanceRelation]) //group by操作
      .filter { case (_, ls) => ls.size > 1 } //如果只取size大于1的进行后续操作
      .map(_._1)
      .toSet

    //更新plan，使得每个实例的expId是唯一的。
    plan transform {
      case l: MultiInstanceRelation if multiAppearance contains l => l.newInstance
    }
  }
}

2.2、LowercaseAttributeReferences

同样是partital function，对当前plan应用，将所有匹配的如UnresolvedRelation的别名alise转换为小写，将Subquery的别名也转换为小写。

总结：这是一个使属性名大小写不敏感的Rule，因为它将所有属性都to lower case了。

object LowercaseAttributeReferences extends Rule[LogicalPlan] {
  def apply(plan: LogicalPlan): LogicalPlan = plan transform {
    case UnresolvedRelation(databaseName, name, alias) =>
      UnresolvedRelation(databaseName, name, alias.map(_.toLowerCase))
    case Subquery(alias, child) => Subquery(alias.toLowerCase, child)
    case q: LogicalPlan => q transformExpressions {
      case s: Star => s.copy(table = s.table.map(_.toLowerCase))
      case UnresolvedAttribute(name) => UnresolvedAttribute(name.toLowerCase)
      case Alias(c, name) => Alias(c, name.toLowerCase)()
      case GetField(c, name) => GetField(c, name.toLowerCase)
    }
  }
}

2.3、ResolveReferences

将Sql parser解析出来的UnresolvedAttribute全部都转为对应的实际的catalyst.expressions.AttributeReference AttributeReferences

这里调用了logical plan 的resolve方法，将属性转为NamedExepression。

object ResolveReferences extends Rule[LogicalPlan] {
  def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
    case q: LogicalPlan if q.childrenResolved =>
      logger.trace(s"Attempting to resolve ${q.simpleString}")
      q transformExpressions {
        case u @ UnresolvedAttribute(name) =>
          // Leave unchanged if resolution fails.  Hopefully will be resolved next round.
          val result = q.resolve(name).getOrElse(u)//转化为NamedExpression
          logger.debug(s"Resolving $u to $result")
          result
      }
  }
}

2.4、 ResolveRelations

这个比较好理解，还记得前面Sql parser吗，比如select * from src，这个src表parse后就是一个UnresolvedRelation节点。

这一步ResolveRelations调用了catalog这个对象。Catalog对象里面维护了一个tableName,Logical Plan的HashMap结果。

通过这个Catalog目录来寻找当前表的结构，从而从中解析出这个表的字段，如UnResolvedRelations 会得到一个tableWithQualifiers。（即表和字段） 

这也解释了为什么流程图那，我会画一个catalog在上面，因为它是Analyzer工作时需要的meta data。

object ResolveRelations extends Rule[LogicalPlan] {
    def apply(plan: LogicalPlan): LogicalPlan = plan transform {
      case UnresolvedRelation(databaseName, name, alias) =>
        catalog.lookupRelation(databaseName, name, alias)
    }
  }

2.5、ImplicitGenerate

如果在select语句里只有一个表达式，而且这个表达式是一个Generator（Generator是一个1条记录生成到N条记录的映射）

当在解析逻辑计划时，遇到Project节点的时候，就可以将它转换为Generate类（Generate类是将输入流应用一个函数，从而生成一个新的流）。

object ImplicitGenerate extends Rule[LogicalPlan] {
  def apply(plan: LogicalPlan): LogicalPlan = plan transform {
    case Project(Seq(Alias(g: Generator, _)), child) =>
      Generate(g, join = false, outer = false, None, child)
  }
}

2.6 StarExpansion

在Project操作符里，如果是*符号，即select * 语句，可以将所有的references都展开，即将select * 中的*展开成实际的字段。

  object StarExpansion extends Rule[LogicalPlan] {
    def apply(plan: LogicalPlan): LogicalPlan = plan transform {
      // Wait until children are resolved
      case p: LogicalPlan if !p.childrenResolved => p
      // If the projection list contains Stars, expand it.
      case p @ Project(projectList, child) if containsStar(projectList) =>
        Project(
          projectList.flatMap {
            case s: Star => s.expand(child.output) //展开，将输入的Attributeexpand(input: Seq[Attribute]) 转化为Seq[NamedExpression]
            case o => o :: Nil
          },
          child)
      case t: ScriptTransformation if containsStar(t.input) =>
        t.copy(
          input = t.input.flatMap {
            case s: Star => s.expand(t.child.output)
            case o => o :: Nil
          }
        )
      // If the aggregate function argument contains Stars, expand it.
      case a: Aggregate if containsStar(a.aggregateExpressions) =>
        a.copy(
          aggregateExpressions = a.aggregateExpressions.flatMap {
            case s: Star => s.expand(a.child.output)
            case o => o :: Nil
          }
        )
    }
    /**
     * Returns true if `exprs` contains a [[Star]].
     */
    protected def containsStar(exprs: Seq[Expression]): Boolean =
      exprs.collect { case _: Star => true }.nonEmpty
  }
}

2.7 ResolveFunctions

这个和ResolveReferences差不多，这里主要是对udf进行resolve。

将这些UDF都在FunctionRegistry里进行查找。

object ResolveFunctions extends Rule[LogicalPlan] {
  def apply(plan: LogicalPlan): LogicalPlan = plan transform {
    case q: LogicalPlan =>
      q transformExpressions {
        case u @ UnresolvedFunction(name, children) if u.childrenResolved =>
          registry.lookupFunction(name, children) //看是否注册了当前udf
      }
  }
}

2.8 GlobalAggregates

全局的聚合，如果遇到了Project就返回一个Aggregate.

object GlobalAggregates extends Rule[LogicalPlan] {
  def apply(plan: LogicalPlan): LogicalPlan = plan transform {
    case Project(projectList, child) if containsAggregates(projectList) =>
      Aggregate(Nil, projectList, child)
  }

  def containsAggregates(exprs: Seq[Expression]): Boolean = {
    exprs.foreach(_.foreach {
      case agg: AggregateExpression => return true
      case _ =>
    })
    false
  }
}

2.9 typeCoercionRules

这个是Hive里的兼容SQL语法，比如将String和Int互相转换，不需要显示的调用cast xxx  as yyy了。如StringToIntegerCasts。

val typeCoercionRules =
  PropagateTypes ::
  ConvertNaNs ::
  WidenTypes ::
  PromoteStrings ::
  BooleanComparisons ::
  BooleanCasts ::
  StringToIntegralCasts ::
  FunctionArgumentConversion ::
  CastNulls ::
  Nil

2.10 EliminateAnalysisOperators

将分析的操作符移除，这里仅支持2种，一种是Subquery需要移除，一种是LowerCaseSchema。这些节点都会从Logical Plan里移除。

 

object EliminateAnalysisOperators extends Rule[LogicalPlan] {
  def apply(plan: LogicalPlan): LogicalPlan = plan transform {
    case Subquery(_, child) => child //遇到Subquery,不反悔本身，返回它的Child，即删除了该元素
    case LowerCaseSchema(child) => child
  }
}

三、实践

  补充昨天DEBUG的一个例子，这个例子证实了如何将上面的规则应用到Unresolved Logical Plan：

  当传递sql语句的时候，的确调用了ResolveReferences将mobile解析成NamedExpression。

  可以对照这看执行流程，左边是Unresolved Logical Plan，右边是Resoveld Logical Plan。

  先是执行了Batch Resolution，eg: 调用ResovelRalation这个RUle来使 Unresovled Relation 转化为 SparkLogicalPlan并通过Catalog找到了其对于的字段属性。

  然后执行了Batch Analysis Operator。eg：调用EliminateAnalysisOperators来将SubQuery给remove掉了。

  可能格式显示的不太好，可以向右边拖动下滚动轴看下结果。 ：） 

  

val exec = sqlContext.sql("select mobile as mb, sid as id, mobile*2 multi2mobile, count(1) times from (select * from temp_shengli_mobile)a where pfrom_id=0.0 group by mobile, sid,  mobile*2")
14/07/21 18:23:32 DEBUG SparkILoop$SparkILoopInterpreter: Invoking: public static java.lang.String $line47.$eval.$print()
14/07/21 18:23:33 INFO Analyzer: Max iterations (2) reached for batch MultiInstanceRelations
14/07/21 18:23:33 INFO Analyzer: Max iterations (2) reached for batch CaseInsensitiveAttributeReferences
14/07/21 18:23:33 DEBUG Analyzer$ResolveReferences$: Resolving 'pfrom_id to pfrom_id#5
14/07/21 18:23:33 DEBUG Analyzer$ResolveReferences$: Resolving 'mobile to mobile#2
14/07/21 18:23:33 DEBUG Analyzer$ResolveReferences$: Resolving 'sid to sid#1
14/07/21 18:23:33 DEBUG Analyzer$ResolveReferences$: Resolving 'mobile to mobile#2
14/07/21 18:23:33 DEBUG Analyzer$ResolveReferences$: Resolving 'mobile to mobile#2
14/07/21 18:23:33 DEBUG Analyzer$ResolveReferences$: Resolving 'sid to sid#1
14/07/21 18:23:33 DEBUG Analyzer$ResolveReferences$: Resolving 'mobile to mobile#2
14/07/21 18:23:33 DEBUG Analyzer:
=== Result of Batch Resolution ===
!Aggregate ['mobile,'sid,('mobile * 2) AS c2#27], ['mobile AS mb#23,'sid AS id#24,('mobile * 2) AS multi2mobile#25,COUNT(1) AS times#26L]   Aggregate [mobile#2,sid#1,(CAST(mobile#2, DoubleType) * CAST(2, DoubleType)) AS c2#27], [mobile#2 AS mb#23,sid#1 AS id#24,(CAST(mobile#2, DoubleType) * CAST(2, DoubleType)) AS multi2mobile#25,COUNT(1) AS times#26L]
! Filter ('pfrom_id = 0.0)                                                                                                                   Filter (CAST(pfrom_id#5, DoubleType) = 0.0)
   Subquery a                                                                                                                                 Subquery a
!   Project [*]                                                                                                                                Project [data_date#0,sid#1,mobile#2,pverify_type#3,create_time#4,pfrom_id#5,p_status#6,pvalidate_time#7,feffect_time#8,plastupdate_ip#9,update_time#10,status#11,preserve_int#12]
!    UnresolvedRelation None, temp_shengli_mobile, None                                                                                         Subquery temp_shengli_mobile
!                                                                                                                                                SparkLogicalPlan (ExistingRdd [data_date#0,sid#1,mobile#2,pverify_type#3,create_time#4,pfrom_id#5,p_status#6,pvalidate_time#7,feffect_time#8,plastupdate_ip#9,update_time#10,status#11,preserve_int#12], MapPartitionsRDD[4] at mapPartitions at basicOperators.scala:174)

14/07/21 18:23:33 DEBUG Analyzer:
=== Result of Batch AnalysisOperators ===
!Aggregate ['mobile,'sid,('mobile * 2) AS c2#27], ['mobile AS mb#23,'sid AS id#24,('mobile * 2) AS multi2mobile#25,COUNT(1) AS times#26L]   Aggregate [mobile#2,sid#1,(CAST(mobile#2, DoubleType) * CAST(2, DoubleType)) AS c2#27], [mobile#2 AS mb#23,sid#1 AS id#24,(CAST(mobile#2, DoubleType) * CAST(2, DoubleType)) AS multi2mobile#25,COUNT(1) AS times#26L]
! Filter ('pfrom_id = 0.0)                                                                                                                   Filter (CAST(pfrom_id#5, DoubleType) = 0.0)
!  Subquery a                                                                                                                                 Project [data_date#0,sid#1,mobile#2,pverify_type#3,create_time#4,pfrom_id#5,p_status#6,pvalidate_time#7,feffect_time#8,plastupdate_ip#9,update_time#10,status#11,preserve_int#12]
!   Project [*]                                                                                                                                SparkLogicalPlan (ExistingRdd [data_date#0,sid#1,mobile#2,pverify_type#3,create_time#4,pfrom_id#5,p_status#6,pvalidate_time#7,feffect_time#8,plastupdate_ip#9,update_time#10,status#11,preserve_int#12], MapPartitionsRDD[4] at mapPartitions at basicOperators.scala:174)
!    UnresolvedRelation None, temp_shengli_mobile, None

四、总结

    本文从源代码角度分析了Analyzer在对Sql Parser解析出的UnResolve Logical Plan 进行analyze的过程中，所执行的流程。

    流程是实例化一个SimpleAnalyzer，定义一些Batch，然后遍历这些Batch在RuleExecutor的环境下，执行Batch里面的Rules，每个Rule会对Unresolved Logical Plan进行Resolve，有些可能不能一次解析出，需要多次迭代，直到达到max迭代次数或者达到fix point。这里Rule里比较常用的就是ResolveReferences、ResolveRelations、StarExpansion、GlobalAggregates、typeCoercionRules和EliminateAnalysisOperators。

 

 

——EOF——

原创文章，转载请注明：

转载自：OopsOutOfMemory盛利的Blog，作者： OopsOutOfMemory

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