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Posted to reviews@spark.apache.org by "ulysses-you (via GitHub)" <gi...@apache.org> on 2023/03/15 15:42:22 UTC
[GitHub] [spark] ulysses-you opened a new pull request, #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut conditional expression
ulysses-you opened a new pull request, #40446:
URL: https://github.com/apache/spark/pull/40446
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### What changes were proposed in this pull request?
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Add a new config to shortcut subexpression elimination for conditional expression.
The subexpression in conditional expression may not need to eval even if it appears more than once.
e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
### Why are the changes needed?
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Please clarify why the changes are needed. For instance,
1. If you propose a new API, clarify the use case for a new API.
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avoid eval unnecessary expression.
### Does this PR introduce _any_ user-facing change?
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no
### How was this patch tested?
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add test
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[GitHub] [spark] viirya commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "viirya (via GitHub)" <gi...@apache.org>.
viirya commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138097640
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
+ }
+ if (shortcut) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ alwaysEvaluated.map {
+ case and: And => and.left
+ case or: Or => or.left
+ case other => other
+ }
Review Comment:
Hmm, if other expression (e.g. `or.right`) is not added into recursing list, how can we look into if it needs to be eliminated? If `or.left` is false, it will be evaluated, isn't?
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut conditional expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138066754
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -130,7 +133,19 @@ class EquivalentExpressions {
// 2. ConditionalExpression: use its children that will always be evaluated.
private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case c: ConditionalExpression =>
+ if (shortcut) {
+ // The subexpression in conditional expression may not need to eval even if it appears
Review Comment:
make sense, addressed ！
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1139888574
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
Review Comment:
shall we match `And`/`Or` here?
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1142906959
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -125,13 +128,27 @@ class EquivalentExpressions {
}
}
+ private def skipForShortcut(expr: Expression): Expression = {
+ if (skipForShortcutEnable) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ expr match {
+ case and: And => skipForShortcut(and.left)
Review Comment:
yea it is the fact, but after second thought the `updateExprTree` has side effect `updateExprInMap` during recursion. If we decide to skip for shortcut, is it better to return the final valid expression in one shot ?
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1139981736
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
Review Comment:
Not need, the next round will cover it. I added some tests to confirm that `And` is not the root node.
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1140038457
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
Review Comment:
oh, I see it. The actually root expression is `If` which is the `ConditionalExpression`. Let me upadte it and the outdate test.
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1140296638
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -125,13 +128,27 @@ class EquivalentExpressions {
}
}
+ private def skipForShortcut(expr: Expression): Expression = {
+ if (skipForShortcutEnable) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ expr match {
+ case and: And => skipForShortcut(and.left)
Review Comment:
`childrenToRecurse` is recursive, so `skipForShortcut` doesn't need to be recursive.
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[GitHub] [spark] viirya commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "viirya (via GitHub)" <gi...@apache.org>.
viirya commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138095296
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala:
##########
@@ -864,6 +864,14 @@ object SQLConf {
.checkValue(_ >= 0, "The maximum must not be negative")
.createWithDefault(100)
+ val SUBEXPRESSION_ELIMINATION_SKIP_FOR_SHORTCUT_EXPR =
+ buildConf("spark.sql.subexpressionElimination.skipForShortcutExpr")
+ .internal()
+ .doc("When true, shortcut eliminate subexpression with `AND`, `OR`.")
Review Comment:
The description is very unclear. Can you add some more?
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138102904
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
+ }
+ if (shortcut) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ alwaysEvaluated.map {
+ case and: And => and.left
+ case or: Or => or.left
+ case other => other
+ }
Review Comment:
It is why we add a new config with disabled by default. We can not decide which subexpression would be evaluated before running. When enable this config, it assumes that the left child is a shotcut, then the righ child can be skipped whatever it contains common subexpression.
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[GitHub] [spark] cloud-fan closed pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan closed pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
URL: https://github.com/apache/spark/pull/40446
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1142906959
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -125,13 +128,27 @@ class EquivalentExpressions {
}
}
+ private def skipForShortcut(expr: Expression): Expression = {
+ if (skipForShortcutEnable) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ expr match {
+ case and: And => skipForShortcut(and.left)
Review Comment:
yea it is the fact, but after second though the `updateExprTree` has side effect `updateExprInMap` during recursion. If we decide to skip for shortcut, is it better to return the final valid expression in one shot ?
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1143112674
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -125,13 +128,27 @@ class EquivalentExpressions {
}
}
+ private def skipForShortcut(expr: Expression): Expression = {
+ if (skipForShortcutEnable) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ expr match {
+ case and: And => skipForShortcut(and.left)
Review Comment:
I'm a bit worried about inconsistency. `childrenToRecurse` is not recursive either and it seems messy if we only make `skipForShortcut` recursive.
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[GitHub] [spark] ulysses-you commented on pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut conditional expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on PR #40446:
URL: https://github.com/apache/spark/pull/40446#issuecomment-1471123749
cc @viirya @cloud-fan thank you
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1140042906
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
+ }
+ if (skipShortcut) {
Review Comment:
changed to `skipForShortcut` which aligns with config name
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1143251312
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -125,13 +128,27 @@ class EquivalentExpressions {
}
}
+ private def skipForShortcut(expr: Expression): Expression = {
+ if (skipForShortcutEnable) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ expr match {
+ case and: And => skipForShortcut(and.left)
Review Comment:
make sense, it should consistent with childrenToRecurse
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut conditional expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138016464
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -130,7 +133,19 @@ class EquivalentExpressions {
// 2. ConditionalExpression: use its children that will always be evaluated.
private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case c: ConditionalExpression =>
+ if (shortcut) {
+ // The subexpression in conditional expression may not need to eval even if it appears
Review Comment:
why only in conditional expression? `where or(a, and(b, b))` has the same problem, right?
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1139980442
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
+ }
+ if (shortcut) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ alwaysEvaluated.map {
+ case and: And => and.left
+ case or: Or => or.left
+ case other => other
+ }
Review Comment:
It's a kind of lazy evaluation. I remember before that pr attempts https://github.com/apache/spark/pull/32977 , and there is some issues @viirya memtioned https://github.com/apache/spark/pull/32977#pullrequestreview-690266902.
It seems the main issue is that, the method will go to large if we make each common subexpression evaluation lazy. Something like:
```
def common_subexpression_1() {
if (isnull) {
// evaluate
} else {
// return exists value
}
}
```
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138102904
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
+ }
+ if (shortcut) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ alwaysEvaluated.map {
+ case and: And => and.left
+ case or: Or => or.left
+ case other => other
+ }
Review Comment:
It is why we add a new config with disabled by default. We can not decide which subexpression would be evaluated before running. When enable this config, it assumes that the left child is a shotcut, then the right child can be skipped whatever it contains common subexpression.
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut conditional expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138020573
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -130,7 +133,19 @@ class EquivalentExpressions {
// 2. ConditionalExpression: use its children that will always be evaluated.
private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case c: ConditionalExpression =>
+ if (shortcut) {
+ // The subexpression in conditional expression may not need to eval even if it appears
Review Comment:
IIUC, CSE only supports project and aggregate. `Predicate` seems not likely appear without conditional expr.
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[GitHub] [spark] ulysses-you commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "ulysses-you (via GitHub)" <gi...@apache.org>.
ulysses-you commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138120937
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala:
##########
@@ -864,6 +864,14 @@ object SQLConf {
.checkValue(_ >= 0, "The maximum must not be negative")
.createWithDefault(100)
+ val SUBEXPRESSION_ELIMINATION_SKIP_FOR_SHORTCUT_EXPR =
+ buildConf("spark.sql.subexpressionElimination.skipForShortcutExpr")
+ .internal()
+ .doc("When true, shortcut eliminate subexpression with `AND`, `OR`.")
Review Comment:
sure, thank you @viirya
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut conditional expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138040356
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -130,7 +133,19 @@ class EquivalentExpressions {
// 2. ConditionalExpression: use its children that will always be evaluated.
private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case c: ConditionalExpression =>
+ if (shortcut) {
+ // The subexpression in conditional expression may not need to eval even if it appears
Review Comment:
not likely, but possible, `select or(a, and(b, b))` is also valid.
BTW, I think we should not enable this new change by default, as it may lead to perf regression.
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1140000835
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
+ }
+ if (skipShortcut) {
Review Comment:
`skipShortCut` means we need to handle the shortcut expressions to skip CSE.
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[GitHub] [spark] cloud-fan commented on pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on PR #40446:
URL: https://github.com/apache/spark/pull/40446#issuecomment-1479648779
thanks, merging to master!
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut conditional expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1138011206
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala:
##########
@@ -864,6 +864,15 @@ object SQLConf {
.checkValue(_ >= 0, "The maximum must not be negative")
.createWithDefault(100)
+ val SUBEXPRESSION_ELIMINATION_SHORTCUT_ENABLE =
+ buildConf("spark.sql.subexpressionElimination.shortcut.enabled")
Review Comment:
```suggestion
buildConf("spark.sql.subexpressionElimination.skipForShortcutExpr")
```
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1139887759
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -23,14 +23,17 @@ import scala.collection.mutable
import org.apache.spark.sql.catalyst.expressions.codegen.CodegenFallback
import org.apache.spark.sql.catalyst.expressions.objects.LambdaVariable
+import org.apache.spark.sql.internal.SQLConf
import org.apache.spark.util.Utils
/**
* This class is used to compute equality of (sub)expression trees. Expressions can be added
* to this class and they subsequently query for expression equality. Expression trees are
* considered equal if for the same input(s), the same result is produced.
*/
-class EquivalentExpressions {
+class EquivalentExpressions(
+ shortcut: Boolean = SQLConf.get.subexpressionEliminationSkipForShotcutExpr) {
Review Comment:
```suggestion
skipShortcut: Boolean = SQLConf.get.subexpressionEliminationSkipForShotcutExpr) {
```
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1140001228
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
+ }
+ if (skipShortcut) {
Review Comment:
maybe `skipInShortcut` is a clearer name
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1139893632
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
+ }
+ if (shortcut) {
+ // The subexpression may not need to eval even if it appears more than once.
+ // e.g., `if(or(a, and(b, b)))`, the expression `b` would be skipped if `a` is true.
+ alwaysEvaluated.map {
+ case and: And => and.left
+ case or: Or => or.left
+ case other => other
+ }
Review Comment:
Another idea is to make CSE more dynamic: only evaluate it if its first appearance needs to be evaluated. It can handle `ConditionalExpression` as well but is much harder to implement.
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[GitHub] [spark] cloud-fan commented on a diff in pull request #40446: [SPARK-42815][SQL] Subexpression elimination support shortcut expression
Posted by "cloud-fan (via GitHub)" <gi...@apache.org>.
cloud-fan commented on code in PR #40446:
URL: https://github.com/apache/spark/pull/40446#discussion_r1140005524
##########
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/EquivalentExpressions.scala:
##########
@@ -128,10 +131,23 @@ 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. ConditionalExpression: use its children that will always be evaluated.
- private def childrenToRecurse(expr: Expression): Seq[Expression] = expr match {
- case _: CodegenFallback => Nil
- case c: ConditionalExpression => c.alwaysEvaluatedInputs
- case other => other.children
+ private def childrenToRecurse(expr: Expression): Seq[Expression] = {
+ val alwaysEvaluated = expr match {
+ case _: CodegenFallback => Nil
+ case c: ConditionalExpression => c.alwaysEvaluatedInputs
+ case other => other.children
Review Comment:
The tests are correct but I'm confused about why the code works... if `And` is a root expression, we blindly take all its children here, right?
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