一、概述

二、实现

1
2
3
4
5
6
7
8
9
10
11
12
13
14
def apply(plan: LogicalPlan): LogicalPlan = {
  val pushdownRules = Seq[LogicalPlan => LogicalPlan] (
    createScanBuilder,
    pushDownSample,
    pushDownFilters,
    pushDownAggregates,
    pushDownLimitAndOffset,
    buildScanWithPushedAggregate,
    pruneColumns)

  pushdownRules.foldLeft(plan) { (newPlan, pushDownRule) =>
    pushDownRule(newPlan)
  }
}

2.1. createScanBuilder()

$createScanBuilder()$ 方法对 DataSourceV2Relation 类型转换为 ScanBuilderHolder，后续的 $pushDownFilters()$ 、$pushDownAggregates()$ 规则则是基于 ScanBuilderHolder 来进行转换

如果有遇到 ScanBuilderHolder 类型才会进行 DataSource V2 特有的规则转换～

所以DataSourceV2Relation是从哪里来的是关键～🤔️？
在 RULE ResolveRelations 中会进行 UnresolvedRelation 到 DataSourceV2Relation 或是 UnresolvedCatalogRelation 的转换:

1
2
3
4
private def createScanBuilder(plan: LogicalPlan) = plan.transform {
  case r: DataSourceV2Relation =>
    ScanBuilderHolder(r.output, r, r.table.asReadable.newScanBuilder(r.options))
}