sarutak opened a new pull request #34765:
URL: https://github.com/apache/spark/pull/34765
### What changes were proposed in this pull request?
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This PR fixes an issue that `CollectMetrics` performs twice if it's followed
by global sort like as follows.
```
val df = spark.range(100)
.observe(
name = "my_event",
min($"id").as("min_val"),
max($"id").as("max_val"),
sum($"id"),
count(when($"id" % 2 === 0, 1)).as("num_even"))
.sort($"id".desc)
```
The expected statistics calculated by `CollectMetrics` is `[0,99,4950,50]`
but the actual result is `[0,99,9900,100]`.
The reason is that jobs for sampling can run before the global sort, which
performs extra `CollectMetrics`.
https://github.com/apache/spark/blob/e7fa28930dce468df02b5915e1792ada758a96e3/core/src/main/scala/org/apache/spark/Partitioner.scala#L171
https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/Partitioner.scala#L195
The solution this PR proposes to introduce a property
`spark.job.isSamplingJob` which is intended to be get/set internally.
Before the sampling jobs run, Spark sets the property, and reset it after
the jobs finish.
Then, `CollectMetrics` can judge a task is whether of a sampling job or not.
### Why are the changes needed?
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Bug fix.
### Does this PR introduce _any_ user-facing change?
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No.
### How was this patch tested?
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New test.
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