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new 5ab28627719f [SPARK-58588][SQL] Return the broadcast hash join build
side from JoinSelectionHelper instead of a Boolean
5ab28627719f is described below
commit 5ab28627719fa1234cebe5df295c02b50851d3d1
Author: YangJie <[email protected]>
AuthorDate: Mon Aug 10 09:48:28 2026 +0800
[SPARK-58588][SQL] Return the broadcast hash join build side from
JoinSelectionHelper instead of a Boolean
### What changes were proposed in this pull request?
`canPlanAsBroadcastHashJoin` already computed an `Option[BuildSide]`
internally and then discarded the direction with `.isDefined`. A caller that
needs the direction therefore had to reimplement the same composition:
`PushDownJoinThroughUnion` (SPARK-58449) did exactly that, so one planner
decision was modelled twice, with each model incomplete and the coupling
invisible in the code.
This PR lifts the composition into
`JoinSelectionHelper.getBroadcastHashJoinBuildSide`, which returns
`Option[BuildSide]`, and redefines `canPlanAsBroadcastHashJoin` as `.isDefined`
on it. The truth table of `canPlanAsBroadcastHashJoin` is unchanged, including
its two deliberate over-approximations of `JoinSelection`: join keys no hash
join supports still reach the size branch, and the method does not model
`SHUFFLE_MERGE` or `SHUFFLE_REPLICATE_NL` hints. Both are now stated in the sc
[...]
`PushDownJoinThroughUnion` then drops its own `canPlanAsBroadcastHashJoin`
conjunct, since `None` from the new method already carries the equi-key
requirement, and shares a `branchJoin` helper between the rewrite and the
guard's probe plan. The probe now rewrites the join condition to the branch
output, which the previous guard did not need to do because it never extracted
equi-join keys.
Making the helper fully faithful to `JoinSelection` would mean returning
`None` under a `SHUFFLE_MERGE` or `SHUFFLE_REPLICATE_NL` hint. That flips
`canPlanAsBroadcastHashJoin` from true to false for a hinted join whose size
still qualifies, which changes what `PushDownLeftSemiAntiJoin` pushes down, so
it is a behavior change rather than a refactor and is left for a separate
ticket.
### Why are the changes needed?
Two partial models of the same planner decision drift apart. Strengthening
one of them, for example teaching `canPlanAsBroadcastHashJoin` about a hint it
currently ignores, silently leaves the other stale, and nothing in the code
says the two have to agree.
### Does this PR introduce _any_ user-facing change?
No. `canPlanAsBroadcastHashJoin` keeps its truth table, and
`spark.sql.optimizer.pushDownJoinThroughUnion.enabled` remains false by default.
### How was this patch tested?
`JoinSuite.assertJoin` now also asserts that
`getBroadcastHashJoinBuildSide` agrees with the build side the planner picked,
which covers every case in that suite that reaches a broadcast hash join.
`JoinSelectionHelperSuite` gains five cases asserting the direction itself: a
hint on either or both sides, the fall back to the smaller side, a shuffle hash
hint, no equi-join keys, and a null-aware anti join.
The direction had no coverage before this PR, so both were checked by
mutation: inverting `getSmallerSide` fails four cases, and returning
`BuildLeft` for the null-aware anti join fails exactly the new case for it.
Existing suites pass: `JoinSelectionHelperSuite` (19),
`PushDownJoinThroughUnionSuite` in catalyst (24) and core (9), and `JoinSuite`
(58).
### Was this patch authored or co-authored using generative AI tooling?
Generated-by: Claude Code
Closes #57790 from LuciferYang/SPARK-planned-broadcast-buildside.
Authored-by: YangJie <[email protected]>
Signed-off-by: yangjie01 <[email protected]>
(cherry picked from commit 213315948949987ef48dac6c8b8fa467a016afb2)
Signed-off-by: yangjie01 <[email protected]>
---
.../optimizer/PushDownJoinThroughUnion.scala | 87 ++++++++++++----------
.../spark/sql/catalyst/optimizer/joins.scala | 38 +++++++---
.../optimizer/JoinSelectionHelperSuite.scala | 52 +++++++++++++
.../scala/org/apache/spark/sql/JoinSuite.scala | 8 ++
4 files changed, 138 insertions(+), 47 deletions(-)
diff --git
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PushDownJoinThroughUnion.scala
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PushDownJoinThroughUnion.scala
index 65c2f63c463e..5454c6d88b00 100644
---
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PushDownJoinThroughUnion.scala
+++
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PushDownJoinThroughUnion.scala
@@ -57,12 +57,8 @@ case class PushDownJoinThroughUnion(override val conf:
SQLConf)
plan.transformUpWithPruning(
_.containsAllPatterns(JOIN, UNION), ruleId) {
- case join @ Join(u: Union, right, joinType, joinCond, hint)
+ case join @ Join(u: Union, right, joinType, _, _)
if (joinType == Inner || joinType == LeftOuter) &&
- // Requires equi-join keys, and rejects the join when a shuffle hash
hint already decided
- // the strategy. The check below adds the build side direction, which
this one does not
- // constrain.
- canPlanAsBroadcastHashJoin(join, conf) &&
broadcastsRightForEveryBranch(u, join) &&
// Exclude right subtrees containing subqueries, as
DeduplicateRelations
// may not correctly handle correlated references when cloning.
@@ -79,53 +75,68 @@ case class PushDownJoinThroughUnion(override val conf:
SQLConf)
val deduped = dedupRight(right)
(deduped, AttributeMap(right.output.zip(deduped.output)))
}
- val leftRewrites = AttributeMap(unionHeadOutput.zip(child.output))
- val newCond = joinCond.map(_.transform {
- case a: Attribute if leftRewrites.contains(a) => leftRewrites(a)
- case a: Attribute if rightRewrites.contains(a) => rightRewrites(a)
- })
- Join(child, newRight, joinType, newCond, hint)
+ branchJoin(join, unionHeadOutput, child, newRight, rightRewrites)
}
u.withNewChildren(newChildren)
}
}
+ /**
+ * The join for one `Union` branch: the branch on the left, `newRight` on
the right, and the
+ * condition rewritten from the `Union` output to the outputs of both new
children.
+ */
+ private def branchJoin(
+ join: Join,
+ unionHeadOutput: Seq[Attribute],
+ child: LogicalPlan,
+ newRight: LogicalPlan,
+ rightRewrites: AttributeMap[Attribute]): Join = {
+ val leftRewrites = AttributeMap(unionHeadOutput.zip(child.output))
+ val newCond = join.condition.map(_.transform {
+ case a: Attribute if leftRewrites.contains(a) => leftRewrites(a)
+ case a: Attribute if rightRewrites.contains(a) => rightRewrites(a)
+ })
+ Join(child, newRight, join.joinType, newCond, join.hint)
+ }
+
/**
* Whether every join produced by the rewrite is expected to broadcast its
right side.
*
- * `canPlanAsBroadcastHashJoin` is not enough. It holds when either side is
broadcastable, and
- * for an inner join the planner may build from either side, choosing the
smaller one when both
- * qualify. The rewrite replaces the `Union` on the left with one of its
children, so the build
- * side is decided per branch against a smaller left. Any branch that ends
up building from the
- * left leaves its copy of the right side as a plain probe input, which is
not reused, so the
- * right side is read once per such branch instead of once in total.
+ * Asking whether a broadcast hash join is possible is not enough: for an
inner join the planner
+ * may build from either side, choosing the smaller one when both qualify.
The rewrite replaces
+ * the `Union` on the left with one of its children, so the build side is
decided per branch
+ * against a smaller left. Any branch that ends up building from the left
leaves its copy of the
+ * right side as a plain probe input, which is not reused, so the right side
is read once per such
+ * branch instead of once in total.
+ *
+ * `getBroadcastHashJoinBuildSide` returns `None` when the join has no
equi-join keys, so this one
+ * check also carries the requirement the removed
`canPlanAsBroadcastHashJoin` conjunct used to.
+ * It is not a statement about what the planner ends up choosing: with keys
no hash join supports
+ * it still answers from the sizes, while `JoinSelection` falls through to a
sort merge join. A
+ * `SHUFFLE_MERGE` or `SHUFFLE_REPLICATE_NL` hint is handled here rather
than there: the planner
+ * tries those between a hinted broadcast and a size-based one, and falls
back to the sizes only
+ * when the hinted strategy does not apply, so declining to rewrite errs on
the safe side.
*
- * The check follows the planner's broadcast precedence, hints before sizes.
It predicts rather
- * than guarantees the final build side, because later rules and AQE
re-estimate the sizes it
- * reads. It is also all or nothing: one branch small enough to be the build
side blocks the
- * rewrite for the others, trading a missed optimization for never
duplicating a probe side. Only
- * an inner join can build from the left, so for a left outer join this
reduces to asking whether
- * the right side is broadcastable at all.
+ * The result predicts rather than guarantees the final build side, because
later rules and AQE
+ * re-estimate the sizes it reads. It is also all or nothing: one branch
small enough to be the
+ * build side blocks the rewrite for the others, trading a missed
optimization for never
+ * duplicating a probe side. Only an inner join can build from the left, so
for a left outer join
+ * this reduces to asking whether the right side is broadcastable at all.
*/
private def broadcastsRightForEveryBranch(u: Union, join: Join): Boolean = {
- // The planner tries these hints between a hinted broadcast and a
size-based one, so the sizes
- // below are usually not what decides the strategy. When the hinted
strategy turns out not to
- // apply the planner does fall back to a size-based broadcast, so this
errs towards not
- // rewriting. A shuffle hash hint needs no such check: given hash-joinable
keys it makes
- // `canPlanAsBroadcastHashJoin` reject the join, and a broadcast hint that
outranks it is
- // already answered by the hint-only query below.
val hintPicksOtherStrategy =
hintToSortMergeJoin(join.hint) || hintToShuffleReplicateNL(join.hint)
+ val unionHeadOutput = u.children.head.output
u.children.forall { child =>
- // Only the join type, the hints and each side's stats are read below,
so the condition is
- // left as is, still referencing the Union output rather than the branch
output.
- val branchJoin = join.copy(left = child)
- getBroadcastBuildSide(branchJoin, hintOnly = true, conf)
- .orElse {
- if (hintPicksOtherStrategy) None
- else getBroadcastBuildSide(branchJoin, hintOnly = false, conf)
- }
- .contains(BuildRight)
+ // The condition has to be rewritten to the branch output:
`getBroadcastHashJoinBuildSide`
+ // extracts the equi-join keys, which do not resolve against a branch
other than the first.
+ val probe =
+ branchJoin(join, unionHeadOutput, child, join.right,
AttributeMap.empty[Attribute])
+ // A hinted broadcast outranks the hints above, so only a size-based
answer is vetoed.
+ val hinted = getBroadcastBuildSide(probe, hintOnly = true,
conf).isDefined
+ val planned =
+ if (hinted || !hintPicksOtherStrategy)
getBroadcastHashJoinBuildSide(probe, conf) else None
+ planned.contains(BuildRight)
}
}
diff --git
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
index edd63829a711..8988183fa3c9 100644
---
a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
+++
b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/joins.scala
@@ -415,18 +415,38 @@ trait JoinSelectionHelper extends Logging {
result
}
- def canPlanAsBroadcastHashJoin(join: Join, conf: SQLConf): Boolean = join
match {
+ /**
+ * The build side a broadcast hash join would use, or `None` when one is
ruled out by the join
+ * shape or by a hint.
+ *
+ * `Some` does not promise the planner picks a broadcast hash join: a
`SHUFFLE_MERGE` or
+ * `SHUFFLE_REPLICATE_NL` hint is tried before the sizes are consulted, join
keys no hash join
+ * supports send it to a sort merge join, and AQE re-estimates the sizes at
runtime. Within the
+ * broadcast decision itself this does follow the planner's precedence: a
hinted broadcast first,
+ * a hinted shuffle hash join as a veto, then the sizes. Callers that only
need to know whether a
+ * broadcast hash join is possible should use `canPlanAsBroadcastHashJoin`.
+ */
+ def getBroadcastHashJoinBuildSide(join: Join, conf: SQLConf):
Option[BuildSide] = join match {
case ExtractEquiJoinKeys(_, leftKeys, rightKeys, _, _, _, _, _) =>
- val hashJoinSupport = hashJoinSupported(leftKeys, rightKeys)
- val noShufflePlannedBefore =
- !hashJoinSupport || getShuffleHashJoinBuildSide(join, hintOnly = true,
conf).isEmpty
- getBroadcastBuildSide(join, hintOnly = true, conf).isDefined ||
- (noShufflePlannedBefore &&
- getBroadcastBuildSide(join, hintOnly = false, conf).isDefined)
- case j @ ExtractSingleColumnNullAwareAntiJoin(_, _) =>
canBroadcastBySize(j.right, conf)
- case _ => false
+ // A shuffle hash hint outranks a size-based broadcast, so it vetoes
one. Keys no hash join
+ // supports cannot honor that hint either, so it does not veto here; the
sizes then still
+ // produce an answer, which over-approximates `JoinSelection` (it falls
through to a sort
+ // merge join). That over-approximation predates this method and is kept
deliberately, so
+ // that `canPlanAsBroadcastHashJoin` keeps its truth table.
+ val noShufflePlannedBefore = !hashJoinSupported(leftKeys, rightKeys) ||
+ getShuffleHashJoinBuildSide(join, hintOnly = true, conf).isEmpty
+ getBroadcastBuildSide(join, hintOnly = true, conf).orElse {
+ if (noShufflePlannedBefore) getBroadcastBuildSide(join, hintOnly =
false, conf) else None
+ }
+ // `JoinSelection` always builds from the right for this shape.
+ case j @ ExtractSingleColumnNullAwareAntiJoin(_, _) =>
+ if (canBroadcastBySize(j.right, conf)) Some(BuildRight) else None
+ case _ => None
}
+ def canPlanAsBroadcastHashJoin(join: Join, conf: SQLConf): Boolean =
+ getBroadcastHashJoinBuildSide(join, conf).isDefined
+
def canPruneLeft(joinType: JoinType): Boolean = joinType match {
case Inner | LeftSemi | RightOuter => true
case _ => false
diff --git
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinSelectionHelperSuite.scala
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinSelectionHelperSuite.scala
index bac20c6ed353..61ef8be59a88 100644
---
a/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinSelectionHelperSuite.scala
+++
b/sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/JoinSelectionHelperSuite.scala
@@ -171,4 +171,56 @@ class JoinSelectionHelperSuite extends PlanTest with
JoinSelectionHelper {
}
}
+ test("getBroadcastHashJoinBuildSide returns the hinted side") {
+ val equiJoin = join.copy(condition = Some(EqualTo(left.output.head,
right.output.head)))
+ withSQLConf(SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1") {
+ assert(getBroadcastHashJoinBuildSide(
+ equiJoin.copy(hint = JoinHint(hintBroadcast, None)), SQLConf.get) ===
Some(BuildLeft))
+ assert(getBroadcastHashJoinBuildSide(
+ equiJoin.copy(hint = JoinHint(None, hintBroadcast)), SQLConf.get) ===
Some(BuildRight))
+ // Both sides hinted: the smaller one wins, as in
`getBroadcastBuildSide`.
+ assert(getBroadcastHashJoinBuildSide(
+ equiJoin.copy(hint = JoinHint(hintBroadcast, hintBroadcast)),
SQLConf.get) ===
+ Some(BuildRight))
+ }
+ }
+
+ test("getBroadcastHashJoinBuildSide falls back to the smaller side") {
+ val equiJoin = join.copy(condition = Some(EqualTo(left.output.head,
right.output.head)))
+ withSQLConf(SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "10MB") {
+ // Only the right side is under the threshold, so it is the only
candidate.
+ assert(getBroadcastHashJoinBuildSide(equiJoin, SQLConf.get) ===
Some(BuildRight))
+ }
+ withSQLConf(SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "-1") {
+ assert(getBroadcastHashJoinBuildSide(equiJoin, SQLConf.get).isEmpty)
+ }
+ }
+
+ test("getBroadcastHashJoinBuildSide returns None when a shuffle hash hint
applies") {
+ val equiJoin = join.copy(condition = Some(EqualTo(left.output.head,
right.output.head)))
+ withSQLConf(SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "10MB") {
+ assert(getBroadcastHashJoinBuildSide(
+ equiJoin.copy(hint = JoinHint(None, hintShuffleHash)),
SQLConf.get).isEmpty)
+ }
+ }
+
+ test("getBroadcastHashJoinBuildSide returns None without equi-join keys") {
+ withSQLConf(SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "10MB") {
+ assert(getBroadcastHashJoinBuildSide(join, SQLConf.get).isEmpty)
+ }
+ }
+
+ test("getBroadcastHashJoinBuildSide builds from the right for a null-aware
anti join") {
+ val leftKey = left.output.head
+ val rightKey = right.output.head
+ val condition = Or(EqualTo(leftKey, rightKey), IsNull(EqualTo(leftKey,
rightKey)))
+ val nullAwareAntiJoin = Join(left, right, LeftAnti, Some(condition),
JoinHint.NONE)
+
+ withSQLConf(
+ SQLConf.OPTIMIZE_NULL_AWARE_ANTI_JOIN.key -> "true",
+ SQLConf.AUTO_BROADCASTJOIN_THRESHOLD.key -> "10MB") {
+ assert(getBroadcastHashJoinBuildSide(nullAwareAntiJoin, SQLConf.get) ===
Some(BuildRight))
+ }
+ }
+
}
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala
b/sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala
index 7f695e90df88..3c0b00793ca5 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/JoinSuite.scala
@@ -83,6 +83,14 @@ class JoinSuite extends SharedSparkSession with
AdaptiveSparkPlanHelper
canPlanAsBroadcastHashJoin(optimized.asInstanceOf[Join], conf) ===
operators.head.isInstanceOf[BroadcastHashJoinExec],
"canPlanAsBroadcastHashJoin not in sync with join selection codepath!")
+ operators.head match {
+ case bhj: BroadcastHashJoinExec =>
+ assert(
+ getBroadcastHashJoinBuildSide(optimized.asInstanceOf[Join], conf)
+ .contains(bhj.buildSide),
+ "getBroadcastHashJoinBuildSide not in sync with join selection
codepath!")
+ case _ =>
+ }
operators.head
}
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