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[GitHub] [spark] ulysses-you opened a new pull request, #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
ulysses-you opened a new pull request, #36455:
URL: https://github.com/apache/spark/pull/36455
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### What changes were proposed in this pull request?
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Add `ConditionalExpression` trait.
### Why are the changes needed?
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For developers, if a custom conditional like expression contains common sub expression then the evaluation order may be changed since Spark will pull out and eval the common sub expressions first during execution.
Add ConditionalExpression trait is friendly for developers.
### Does this PR introduce _any_ user-facing change?
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no, add a new trait
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Pass existed test
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[GitHub] [spark] viirya commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
viirya commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866405428
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala:
##########
@@ -454,6 +454,33 @@ trait Nondeterministic extends Expression {
protected def evalInternal(input: InternalRow): Any
}
+/**
+ * An expression that contains predicate expression branch, so not all branch will be hit
Review Comment:
```suggestion
* An expression that contains conditional expression branches, so not all branches will be hit
```
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[GitHub] [spark] ulysses-you commented on pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
ulysses-you commented on PR #36455:
URL: https://github.com/apache/spark/pull/36455#issuecomment-1118495383
cc @cloud-fan @viirya
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[GitHub] [spark] cloud-fan closed pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan closed pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
URL: https://github.com/apache/spark/pull/36455
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[GitHub] [spark] cloud-fan commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866433341
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -127,56 +127,18 @@ class EquivalentExpressions {
// There are some special expressions that we should not recurse into all of its children.
// 1. CodegenFallback: it's children will not be used to generate code (call eval() instead)
- // 2. If: common subexpressions will always be evaluated at the beginning, but the true and
- // false expressions in `If` may not get accessed, according to the predicate
- // expression. We should only recurse into the predicate expression.
- // 3. CaseWhen: like `If`, the children of `CaseWhen` only get accessed in a certain
- // condition. We should only recurse into the first condition expression as it
- // will always get accessed.
- // 4. Coalesce: it's also a conditional expression, we should only recurse into the first
- // children, because others may not get accessed.
- // 5. NaNvl: it's a conditional expression, we can only guarantee the left child can be always
- // accessed. And if we hit the left child, the right will not be accessed.
+ // 2. ConditionalExpression: use it's specified expression
Review Comment:
```suggestion
// 2. ConditionalExpression: use its children that will always be evaluated.
```
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[GitHub] [spark] dongjoon-hyun commented on pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
dongjoon-hyun commented on PR #36455:
URL: https://github.com/apache/spark/pull/36455#issuecomment-1119758119
+1 for @cloud-fan 's backporting decision.
Also, cc @MaxGekk
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[GitHub] [spark] cloud-fan commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866056903
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala:
##########
@@ -454,6 +454,33 @@ trait Nondeterministic extends Expression {
protected def evalInternal(input: InternalRow): Any
}
+/**
+ * An expression that contains predicate expression branch, so not all branch will be hit
+ * at runtime. All optimization should be careful with the evaluation order.
+ */
+trait ConditionalExpression extends Expression {
+ /**
+ * Return the expression which can always be hit at runtime, For example:
+ * 1. If: common subexpressions will always be evaluated at the beginning, but the true and
+ * false expressions in `If` may not get accessed, according to the predicate
+ * expression. We should only return the predicate expression.
+ * 2. CaseWhen: like `If`, the children of `CaseWhen` only get accessed in a certain
+ * condition. We should only return the first condition expression as it
+ * will always get accessed.
+ * 3. Coalesce: it's also a conditional expression, we should only return the first child,
+ * because others may not get accessed.
+ * 4. NaNvl: we can only guarantee the left child can be always accessed.
+ * And if we hit the left child, the right will not be accessed.
+ */
+ def head: Expression = children.head
Review Comment:
Since we are doing abstraction here, let's make it more general. I think there are 2 things we need to care about for a condition expression:
1. inputs that will always be evaluated. Today all conditional expressions only have one input that will always be evaluated, but I don't see why it can't be a `Seq`. How about `def alwaysEvaluatedInputs: Seq[Expression]`
2. groups of branches. For each group, at least one branch will be hit at runtime, so that we can eagerly evaluate the common expressions of a group. How about `def branchGroups: Seq[Seq[Expression]]`
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[GitHub] [spark] ulysses-you commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
ulysses-you commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866429527
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala:
##########
@@ -454,6 +454,33 @@ trait Nondeterministic extends Expression {
protected def evalInternal(input: InternalRow): Any
}
+/**
+ * An expression that contains predicate expression branch, so not all branch will be hit
+ * at runtime. All optimization should be careful with the evaluation order.
+ */
+trait ConditionalExpression extends Expression {
+ /**
+ * Return the expression which can always be hit at runtime, For example:
+ * 1. If: common subexpressions will always be evaluated at the beginning, but the true and
+ * false expressions in `If` may not get accessed, according to the predicate
+ * expression. We should only return the predicate expression.
+ * 2. CaseWhen: like `If`, the children of `CaseWhen` only get accessed in a certain
+ * condition. We should only return the first condition expression as it
+ * will always get accessed.
+ * 3. Coalesce: it's also a conditional expression, we should only return the first child,
+ * because others may not get accessed.
+ * 4. NaNvl: we can only guarantee the left child can be always accessed.
+ * And if we hit the left child, the right will not be accessed.
+ */
+ def head: Expression = children.head
Review Comment:
good call, Seq[Expression] is also good to me
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[GitHub] [spark] viirya commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
viirya commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866406148
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala:
##########
@@ -454,6 +454,33 @@ trait Nondeterministic extends Expression {
protected def evalInternal(input: InternalRow): Any
}
+/**
+ * An expression that contains predicate expression branch, so not all branch will be hit
+ * at runtime. All optimization should be careful with the evaluation order.
+ */
+trait ConditionalExpression extends Expression {
+ /**
+ * Return the expression which can always be hit at runtime, For example:
+ * 1. If: common subexpressions will always be evaluated at the beginning, but the true and
+ * false expressions in `If` may not get accessed, according to the predicate
+ * expression. We should only return the predicate expression.
+ * 2. CaseWhen: like `If`, the children of `CaseWhen` only get accessed in a certain
+ * condition. We should only return the first condition expression as it
+ * will always get accessed.
+ * 3. Coalesce: it's also a conditional expression, we should only return the first child,
+ * because others may not get accessed.
+ * 4. NaNvl: we can only guarantee the left child can be always accessed.
+ * And if we hit the left child, the right will not be accessed.
+ */
+ def head: Expression = children.head
Review Comment:
+1 for `Seq[Expression]` for 1.
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[GitHub] [spark] cloud-fan commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866434185
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/conditionalExpressions.scala:
##########
@@ -48,6 +48,14 @@ case class If(predicate: Expression, trueValue: Expression, falseValue: Expressi
override def second: Expression = trueValue
override def third: Expression = falseValue
override def nullable: Boolean = trueValue.nullable || falseValue.nullable
+ /**
+ * Common subexpressions will always be evaluated at the beginning, but the true and
+ * false expressions in `If` may not get accessed, according to the predicate expression.
+ * We should only return the predicate expression.
Review Comment:
I think we can simplify the comment now
```
Only the condition expression will always be evaluated.
```
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[GitHub] [spark] cloud-fan commented on pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on PR #36455:
URL: https://github.com/apache/spark/pull/36455#issuecomment-1119344173
thanks, merging to master/3.3! (I'm backporting this small refactor as we will have a bug fix that relies on it)
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[GitHub] [spark] ulysses-you commented on pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
ulysses-you commented on PR #36455:
URL: https://github.com/apache/spark/pull/36455#issuecomment-1119412422
thank you @cloud-fan @viirya
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[GitHub] [spark] cloud-fan commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866057861
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala:
##########
@@ -454,6 +454,33 @@ trait Nondeterministic extends Expression {
protected def evalInternal(input: InternalRow): Any
}
+/**
+ * An expression that contains predicate expression branch, so not all branch will be hit
+ * at runtime. All optimization should be careful with the evaluation order.
+ */
+trait ConditionalExpression extends Expression {
+ /**
+ * Return the expression which can always be hit at runtime, For example:
+ * 1. If: common subexpressions will always be evaluated at the beginning, but the true and
+ * false expressions in `If` may not get accessed, according to the predicate
+ * expression. We should only return the predicate expression.
+ * 2. CaseWhen: like `If`, the children of `CaseWhen` only get accessed in a certain
+ * condition. We should only return the first condition expression as it
+ * will always get accessed.
+ * 3. Coalesce: it's also a conditional expression, we should only return the first child,
+ * because others may not get accessed.
+ * 4. NaNvl: we can only guarantee the left child can be always accessed.
Review Comment:
let's move the doc to individual expressions.
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[GitHub] [spark] cloud-fan commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866056903
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala:
##########
@@ -454,6 +454,33 @@ trait Nondeterministic extends Expression {
protected def evalInternal(input: InternalRow): Any
}
+/**
+ * An expression that contains predicate expression branch, so not all branch will be hit
+ * at runtime. All optimization should be careful with the evaluation order.
+ */
+trait ConditionalExpression extends Expression {
+ /**
+ * Return the expression which can always be hit at runtime, For example:
+ * 1. If: common subexpressions will always be evaluated at the beginning, but the true and
+ * false expressions in `If` may not get accessed, according to the predicate
+ * expression. We should only return the predicate expression.
+ * 2. CaseWhen: like `If`, the children of `CaseWhen` only get accessed in a certain
+ * condition. We should only return the first condition expression as it
+ * will always get accessed.
+ * 3. Coalesce: it's also a conditional expression, we should only return the first child,
+ * because others may not get accessed.
+ * 4. NaNvl: we can only guarantee the left child can be always accessed.
+ * And if we hit the left child, the right will not be accessed.
+ */
+ def head: Expression = children.head
Review Comment:
Since we are doing abstraction here, let's make it more general. I think there are 2 things we need to care about for a condition expression:
1. inputs that will always be evaluated. Today all conditional expressions only have one input that will always be evaluated, but I don't see why it can't be a `Seq`. How about `def alwaysEvaluatedInputs: Seq[Expression]`
2. groups of branches. For each group, at least one branch will be hit at runtime, so that we can eagerly evaluate the common expressions for a group. How about `def branchGroups: Seq[Seq[Expression]]`
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[GitHub] [spark] cloud-fan commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866435684
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/conditionalExpressions.scala:
##########
@@ -179,6 +187,36 @@ case class CaseWhen(
}
}
+ /**
+ * Like `If`, the children of `CaseWhen` only get accessed in a certain condition.
+ * We should only return the first condition expression as it will always get accessed.
+ */
+ override def alwaysEvaluatedInputs: Seq[Expression] = children.head :: Nil
+
+ override def branchGroups: Seq[Seq[Expression]] = {
+ // We look at subexpressions in conditions and values of `CaseWhen` separately. It is
+ // because a subexpression in conditions will be run no matter which condition is matched
+ // if it is shared among conditions, but it doesn't need to be shared in values. Similarly,
+ // a subexpression among values doesn't need to be in conditions because no matter which
+ // condition is true, it will be evaluated.
+ val conditions = if (branches.length > 1) {
+ branches.map(_._1)
+ } else {
+ // If there is only one branch, the first condition is already covered by
+ // `head` and we should exclude it here.
Review Comment:
```suggestion
// `alwaysEvaluatedInputs` and we should exclude it here.
```
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[GitHub] [spark] cloud-fan commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866435782
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/nullExpressions.scala:
##########
@@ -66,6 +67,19 @@ case class Coalesce(children: Seq[Expression]) extends ComplexTypeMergingExpress
}
}
+ /**
+ * We should only return the first child, because others may not get accessed.
+ */
+ override def alwaysEvaluatedInputs: Seq[Expression] = children.head :: Nil
+
+ override def branchGroups: Seq[Seq[Expression]] = if (children.length > 1) {
+ // If there is only one child, the first child is already covered by
+ // `head` and we should exclude it here.
Review Comment:
```suggestion
// `alwaysEvaluatedInputs` and we should exclude it here.
```
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[GitHub] [spark] cloud-fan commented on a diff in pull request #36455: [SPARK-39105][SQL] Add ConditionalExpression trait
Posted by GitBox <gi...@apache.org>.
cloud-fan commented on code in PR #36455:
URL: https://github.com/apache/spark/pull/36455#discussion_r866433732
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala:
##########
@@ -454,6 +454,23 @@ trait Nondeterministic extends Expression {
protected def evalInternal(input: InternalRow): Any
}
+/**
+ * An expression that contains conditional expression branches, so not all branches will be hit.
+ * All optimization should be careful with the evaluation order.
+ */
+trait ConditionalExpression extends Expression {
+ /**
+ * Return the expression which can always be hit at runtime.
Review Comment:
```suggestion
* Return the children expressions which can always be hit at runtime.
```
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