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[GitHub] [spark] alexeykudinkin opened a new pull request #35808: [WIP][SPARK-38512] Rebased traversal order from "pre-order" to "post-order" for `ResolveFunctions` Rule
alexeykudinkin opened a new pull request #35808:
URL: https://github.com/apache/spark/pull/35808
Rebased traversal order from "pre-order" to "post-order" for `ResolveFunctions` rule to make sure most expressions are able to be resolved in a single pass
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### What changes were proposed in this pull request?
Rebased traversal order from "pre-order" to "post-order" for `ResolveFunctions` rule to make sure most expressions are able to be resolved in a single pass.
This is required to address SPARK-38512
### Why are the changes needed?
ResolveFunctions Rule is implemented incorrectly requiring multiple passes to Resolve Nested Expressions:
While Plan object is traversed correctly in post-order (bottoms-up, `plan.resolveOperatorsUpWithPruning), internally, Plan children though are traversed incorrectly in pre-order (top-down, using `transformExpressionsWithPruning`):
Traversing in pre-order means that attempt is taken to resolve the current node, before its children are resolved, which is incorrect, since the node itself could not be resolved before its children are.
While this is not leading to failures yet, this is taxing on performance – most of the expressions in Spark should be able to be resolved in a single pass (if resolved bottoms-up, take reproducible sample at the bottom). Instead, it currently takes Spark at least N iterations to resolve such expressions, where N is proportional to the depth of the Expression tree.
Example to reproduce:
```
def resolveExpr(spark: SparkSession, exprStr: String, tableSchema: StructType): Expression = {
val expr = spark.sessionState.sqlParser.parseExpression(exprStr)
val analyzer = spark.sessionState.analyzer
val schemaFields = tableSchema.fields
val resolvedExpr = {
val plan: LogicalPlan = Filter(expr, LocalRelation(schemaFields.head, schemaFields.drop(1): _*))
val rules: Seq[Rule[LogicalPlan]] = {
analyzer.ResolveFunctions ::
analyzer.ResolveReferences ::
Nil
}
rules.foldRight(plan)((rule, plan) => rule.apply(plan))
.asInstanceOf[Filter]
.condition
}
resolvedExpr
}
// Invoke with
resolveExpr(spark, "date_format(to_timestamp(B, 'yyyy-MM-dd'), 'MM/dd/yyyy')", StructType(StructField("B", StringType)))
```
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
Adding a regression test.
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[GitHub] [spark] AmplabJenkins commented on pull request #35808: [WIP][SPARK-38512] Rebased traversal order from "pre-order" to "post-order" for `ResolveFunctions` Rule
Posted by GitBox <gi...@apache.org>.
AmplabJenkins commented on pull request #35808:
URL: https://github.com/apache/spark/pull/35808#issuecomment-1064953315
Can one of the admins verify this patch?
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