Hive优化器原理与源码解析系列--优化规则HiveFilterAggregateTransposeRule(十八)

@Override
public boolean matches(RelOptRuleCall call) {
  final Filter filterRel = call.rel(0);
  RexNode condition = filterRel.getCondition();
  if (!HiveCalciteUtil.isDeterministic(condition)) {//判断是否为确定性方法，如果是确定性，并谓词表达式，否则跳出优化。
    return false;
  }
  return super.matches(call);
}

final Filter filterRel = call.rel(0);
final Aggregate aggRel = call.rel(1);
final List<RexNode> conditions =
        RelOptUtil.conjunctions(filterRel.getCondition());//把谓词条件分解成有AND连接行表达式列表
final RexBuilder rexBuilder = filterRel.getCluster().getRexBuilder();
final List<RelDataTypeField> origFields =
        aggRel.getRowType().getFieldList();//获取Aggregate对象引用的字段列表
final int[] adjustments = new int[origFields.size()];
int j = 0;
for (int i : aggRel.getGroupSet()) {//遍历GroupBy字段索引，并向前退
    adjustments[j] = i - j;
    j++;
}

final List<RexNode> pushedConditions = Lists.newArrayList();//存放可下推的表达式列表
final List<RexNode> remainingConditions = Lists.newArrayList();//存放其余不可下推的表达式列表
  //InputFinder：Visitor which builds a bitmap of the inputs used by an expression.
  //bits方法：Returns a bit set describing the inputs used by an expression.
for (RexNode condition : conditions) {//遍历上述分解的，AND连接RexNode列表
    ImmutableBitSet rCols = RelOptUtil.InputFinder.bits(condition);
/**
 *  static class RelOptUtil.RexInputConverter
 * Walks an expression tree, converting the index of RexInputRefs based on some adjustment    factor.
 */
    if (canPush(aggRel, rCols)) {
        pushedConditions.add(
                condition.accept(
                        new RelOptUtil.RexInputConverter(rexBuilder, origFields,
                                aggRel.getInput(0).getRowType().getFieldList(),
                                adjustments)));
    } else {
        remainingConditions.add(condition);
    }
}

final RelBuilder builder = call.builder();
RelNode rel = builder.push(aggRel.getInput()).filter(pushedConditions).build();//把谓词下推到AGG的子输入INPUT
if (rel == aggRel.getInput(0)) {//如果rel和原AGG的输入相同，退出优化。
   return;
}
rel = aggRel.copy(aggRel.getTraitSet(), ImmutableList.of(rel));//复制新生成的已下推的RelNode
rel = builder.push(rel).filter(remainingConditions).build();//再补上剩余的没有下推的谓词条件
call.transformTo(rel);//注册到优化器

private boolean canPush(Aggregate aggregate, ImmutableBitSet rCols) {
    // If the filter references columns not in the group key, we cannot push
    final ImmutableBitSet groupKeys =
            ImmutableBitSet.range(0, aggregate.getGroupSet().cardinality());
    if (!groupKeys.contains(rCols)) {
        return false;
    }
    if (aggregate.indicator) {//标识是否AGG是否使用了GroupSets
      //在谓词表达式中出现的字段引用，都在grouping sets中出现，也是可以下推的。
        for (ImmutableBitSet groupingSet : aggregate.getGroupSets()) {
            if (!groupingSet.contains(rCols)) {
                return false;
            }
        }
    }
    return true;
}