cloud-fan opened a new pull request, #48284:
URL: https://github.com/apache/spark/pull/48284
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### What changes were proposed in this pull request?
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This PR fixes a long-standing reference counting bug in the rule
`InlineCTE`. Let's look at the minimal repro:
```
sql(
"""
|WITH
|t1 AS (SELECT 1 col),
|t2 AS (SELECT * FROM t1)
|SELECT * FROM t2
|""".stripMargin).createTempView("v")
// r1 is un-referenced, but it should not decrease the ref count of t2
inside view v.
val df = sql(
"""
|WITH
|r1 AS (SELECT * FROM v),
|r2 AS (SELECT * FROM v)
|SELECT * FROM r2
|""".stripMargin)
```
The logical plan is something like below
```
WithCTE
CTEDef r1
View v
WithCTE
CTEDef t1
OneRowRelation
CTEDef t2
CTERef t1
CTERef t2
CTEDef r2
View v
WithCTE
CTEDef t1
OneRowRelation
CTEDef t2
CTERef t1
CTERef t2
CTERef r2
```
Ideally, the ref count of `t1`, `t2` and `r2` should be all `1`. They will
be inlined and the final plan is the `OneRowRelation`. However, in
`InlineCTE#buildCTEMap`, when we traverse into `CTEDef r1` and hit `CTERef t2`,
we mistakenly update the out-going-ref-count of `r1`, which means that `r1`
references `t2` and this is totally wrong. Later on, in
`InlineCTE#cleanCTEMap`, we find that `r1` is not referenced at all, so we
decrease the ref count of its out-going-ref, which is `t2`, and the ref count
of `t2` becomes `0`. Finally, in `InlineCTE#inlineCTE`, we leave the plan of
`t2` unchanged because its ref count is `0`, and the plan of `t2` contains
`CTERef t1`. `t2` is still inlined so we end up with `CTERef t1` as the final
plan without the `WithCTE` node.
### Why are the changes needed?
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bug fix
### Does this PR introduce _any_ user-facing change?
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Yes, the query failed before and now can work
### How was this patch tested?
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new test
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no
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