WweiL opened a new pull request, #39843:
URL: https://github.com/apache/spark/pull/39843
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### What changes were proposed in this pull request?
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I tried to understand what was introduced in
https://github.com/apache/spark/pull/36737 and made the code more readable and
added some test. Sharing the credit with @nyingping.
The change in https://github.com/apache/spark/pull/35362 brought a bug when
the `timestamp` is less than 0, i.e. before `1970-01-01 00:00:00 UTC`. Then for
some windows, spark returns a wrong `windowStart` time. The root cause of this
bug is how the module operator(%) works with negative number.
For example,
```
scala> 1 % 3
res0: Int = 1
scala> -1 % 3
res1: Int = -1 // Mathematically it should be 2 here
```
This lead to a wrong calculation result of `windowStart`. For a concrete
example refer to the added comments in
[ResolveTimeWindows.scala](https://github.com/WweiL/oss-spark/blob/fee352e46813cca1f1b6187ea9cfa27124b6049c/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveTimeWindows.scala#L58-L67)
### Why are the changes needed?
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1. If you propose a new API, clarify the use case for a new API.
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This is a bug fix.
Example from the original PR https://github.com/apache/spark/pull/36737:
Here df3 and df4 has time before 1970, so timestamp < 0.
```
val df3 = Seq(
("1969-12-31 00:00:02", 1),
("1969-12-31 00:00:12", 2)).toDF("time", "value")
val df4 = Seq(
(LocalDateTime.parse("1969-12-31T00:00:02"), 1),
(LocalDateTime.parse("1969-12-31T00:00:12"), 2)).toDF("time", "value")
Seq(df3, df4).foreach { df =>
checkAnswer(
df.select(window($"time", "10 seconds", "10 seconds", "5 seconds"),
$"value")
.orderBy($"window.start".asc)
.select($"window.start".cast(StringType),
$"window.end".cast(StringType), $"value"),
Seq(
Row("1969-12-30 23:59:55", "1969-12-31 00:00:05", 1),
Row("1969-12-31 00:00:05", "1969-12-31 00:00:15", 2))
)
}
```
Without the change this would error with:
```
== Results ==
!== Correct Answer - 2 == == Spark Answer - 2 ==
!struct<> struct<CAST(window.start AS
STRING):string,CAST(window.end AS STRING):string,value:int>
![1969-12-30 23:59:55,1969-12-31 00:00:05,1] [1969-12-31
00:00:05,1969-12-31 00:00:15,1]
![1969-12-31 00:00:05,1969-12-31 00:00:15,2] [1969-12-31
00:00:15,1969-12-31 00:00:25,2]
```
Notice how this is shifted with one `slideDuration`. It should start with
`[1969-12-30 23:59:55,1969-12-31 00:00:05,1]` but spark returns `[1969-12-31
00:00:05,1969-12-31 00:00:15,1]`, right-shifted of one `slideDuration` (10
seconds).
### Does this PR introduce _any_ user-facing change?
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No.
### How was this patch tested?
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Unit test.
### Benchmark results:
1. Burak's original Implementation
```
[info] Apple M1 Max
[info] tumbling windows: Best Time(ms) Avg
Time(ms) Stdev(ms) Rate(M/s) Per Row(ns) Relative
[info]
------------------------------------------------------------------------------------------------------------------------
[info] burak version 10
17 14 962.7 1.0 1.0X
[info] Running benchmark: sliding windows
[info] Running case: burak version
[info] Stopped after 16 iterations, 10604 ms
[info] OpenJDK 64-Bit Server VM 11.0.12+7-LTS on Mac OS X 12.5.1
[info] Apple M1 Max
[info] sliding windows: Best Time(ms) Avg
Time(ms) Stdev(ms) Rate(M/s) Per Row(ns) Relative
[info]
------------------------------------------------------------------------------------------------------------------------
[info] burak version 646
663 19 15.5 64.6 1.0X
```
2. Current implementation (buggy)
```
[info] Running benchmark: tumbling windows
[info] Running case: current - buggy
[info] Stopped after 637 iterations, 10008 ms
[info] OpenJDK 64-Bit Server VM 11.0.12+7-LTS on Mac OS X 12.5.1
[info] Apple M1 Max
[info] tumbling windows: Best Time(ms) Avg
Time(ms) Stdev(ms) Rate(M/s) Per Row(ns) Relative
[info]
------------------------------------------------------------------------------------------------------------------------
[info] current - buggy 10
16 12 1042.7 1.0 1.0X
[info] Running benchmark: sliding windows
[info] Running case: current - buggy
[info] Stopped after 16 iterations, 10143 ms
[info] OpenJDK 64-Bit Server VM 11.0.12+7-LTS on Mac OS X 12.5.1
[info] Apple M1 Max
[info] sliding windows: Best Time(ms) Avg
Time(ms) Stdev(ms) Rate(M/s) Per Row(ns) Relative
[info]
------------------------------------------------------------------------------------------------------------------------
[info] current - buggy 617
634 10 16.2 61.7 1.0X
```
3. Purposed change in this PR:
```
[info] Apple M1 Max
[info] tumbling windows: Best Time(ms) Avg
Time(ms) Stdev(ms) Rate(M/s) Per Row(ns) Relative
[info]
------------------------------------------------------------------------------------------------------------------------
[info] purposed change 10
16 11 981.2 1.0 1.0X
[info] Running benchmark: sliding windows
[info] Running case: purposed change
[info] Stopped after 18 iterations, 10122 ms
[info] OpenJDK 64-Bit Server VM 11.0.12+7-LTS on Mac OS X 12.5.1
[info] Apple M1 Max
[info] sliding windows: Best Time(ms) Avg
Time(ms) Stdev(ms) Rate(M/s) Per Row(ns) Relative
[info]
------------------------------------------------------------------------------------------------------------------------
[info] purposed change 548
562 19 18.3 54.8 1.0X
```
Note that I run them separately, because I found that if you run these tests
sequentially, the later one will always get a performance gain. I think the
computer is doing some optimizations.
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