voonhous commented on PR #8579:
URL: https://github.com/apache/hudi/pull/8579#issuecomment-1523138078
> > Results will be different if combineAndUpdateValue is invoked in order
without invoking preCombine.
>
> What is exactly lost here?
# PreCombine + combineAndGetUpdateValue
```
Table schema: {id: int , name: string, price: double, _ts: int}
recordKey: id
precombineField: _ts
Table initial state:
[1 a1_0 10.0 1001]
Table performs an update with an incoming batch that has the following
results (2):
(precombine + combineAndGetUpdateValue)
[
[1 a1_0 11.0 999],
[1 a1_0 null 1001]
]
End state of the table:
[1 a1_0 11.0 1001]
```
This is so as the incoming batch at (2) will be `preCombine` before
performing a `combineAndUpdateValue`.
# combineAndGetUpdateValue ONLY
Results will be different if `combineAndUpdateValue` is invoked in order
without invoking `preCombine`.
Example:
```
Table initial state:
[1 a1_0 10.0 1001]
Table performs an update:
(combineAndGetUpdateValue)
[1 a1_0 11.0 999]
Table performs an update again:
(combineAndGetUpdateValue)
[1 a1_0 null 1001]
End state of the table:
[1 a1_0 10.0 1001]
```
[
[1 a1_0 11.0 999],
[1 a1_0 null 1001]
]
End state of the table:
[1 a1_0 11.0 1001]
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