ueshin opened a new pull request, #54392:
URL: https://github.com/apache/spark/pull/54392
### What changes were proposed in this pull request?
This is a follow-up of apache/spark#54375.
Fixes CoW mode not to break `groupby`.
Delays to disconnect the anchor to when actually being updated.
### Why are the changes needed?
The CoW mode was supported at apache/spark#54375, but it disconnected the
anchor too early, causing to break `groupby`.
```py
>>> import pandas as pd
>>> import pyspark.pandas as ps
>>>
>>> pdf1 = pd.DataFrame({"C": [0.362, 0.227, 1.267, -0.562], "B": [1, 2, 3,
4]})
>>> pdf2 = pd.DataFrame({"A": [1, 1, 2, 2]})
>>>
>>> psdf1 = ps.from_pandas(pdf1)
>>> psdf2 = ps.from_pandas(pdf2)
>>>
>>> pdf1.groupby([pdf1.C, pdf2.A]).agg("sum").sort_index()
B
C A
-0.562 2 4
0.227 1 2
0.362 1 1
1.267 2 3
>>> psdf1.groupby([psdf1.C, psdf2.A]).agg("sum").sort_index()
C B
C A
-0.562 2 -0.562 4
0.227 1 0.227 2
0.362 1 0.362 1
1.267 2 1.267 3
```
### Does this PR introduce _any_ user-facing change?
Yes, it will behave more like pandas 3.
### How was this patch tested?
The existing tests should pass.
### Was this patch authored or co-authored using generative AI tooling?
Codex (GPT-5.3-Codex)
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