JacobZheng0927 opened a new pull request, #43979:
URL: https://github.com/apache/spark/pull/43979
### What changes were proposed in this pull request?
Modify the toJSON return format of CaseWhen to avoid child expressions being
populated multiple times in JSON.
**Before:**
```json
[
{
"class":"org.apache.spark.sql.catalyst.expressions.CaseWhen",
"num-children":3,
"branches":[
{
"product-class":"scala.Tuple2",
"_1":[
{
"class":"org.apache.spark.sql.catalyst.expressions.EqualTo",
"num-children":2,
"left":0,
"right":1
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":"1",
"dataType":"integer"
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":"2",
"dataType":"integer"
}
],
"_2":[
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":"3",
"dataType":"integer"
}
]
}
],
"elseValue":[
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":"4",
"dataType":"integer"
}
]
},
{
"class":"org.apache.spark.sql.catalyst.expressions.EqualTo",
"num-children":2,
"left":0,
"right":1
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":"1",
"dataType":"integer"
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":"2",
"dataType":"integer"
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":"3",
"dataType":"integer"
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":"4",
"dataType":"integer"
}
]
```
**After:**
```json
[
{
"class":"org.apache.spark.sql.catalyst.expressions.CaseWhen",
"num-children":3,
"branches":[
{
"condition":0,
"value":1
}
],
"elseValue":2
},
{
"class":"org.apache.spark.sql.catalyst.expressions.EqualTo",
"num-children":2,
"left":0,
"right":1
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":1,
"dataType":"integer"
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":2,
"dataType":"integer"
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":3,
"dataType":"integer"
},
{
"class":"org.apache.spark.sql.catalyst.expressions.Literal",
"num-children":0,
"value":4,
"dataType":"integer"
}
]
```
### Why are the changes needed?
When executing the toJSON method on an expression nested in more than one
case when, it is easy to cause OOM because the child expression is expanded
multiple times.
eg.
```
CASE
WHEN(`cost` <= 250) THEN '(245-250]'
ELSE CASE
WHEN(`cost` <= 255) THEN '(250-255]'
ELSE CASE
WHEN(`cost` <= 260) THEN '(255-260]'
ELSE CASE
WHEN(`cost` <= 265) THEN '(260-265]'
ELSE '----'
END
END
END
END
END
```
### Does this PR introduce _any_ user-facing change?
Yes. It changes the return result of CaseWhen's toJSON method.
### How was this patch tested?
Unit test
### Was this patch authored or co-authored using generative AI tooling?
No
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