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https://issues.apache.org/jira/browse/SPARK-60066?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ben Hollis updated SPARK-60066:
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Issue Type: Bug (was: Improvement)
> Nested UpdateFields expressions duplicate source expressions
> ------------------------------------------------------------
>
> Key: SPARK-60066
> URL: https://issues.apache.org/jira/browse/SPARK-60066
> Project: Spark
> Issue Type: Bug
> Components: SQL
> Affects Versions: 4.4.0
> Reporter: Ben Hollis
> Priority: Major
>
> Spark represents `Column.withField` as the Catalyst expression
> `UpdateFields`. Before execution, Spark replaces that expression with a new
> struct containing the updated value and a read for every unchanged field.
> Each unchanged-field read contains the complete expression that produces the
> input struct.
>
> When several updates are nested, the input to one replacement contains the
> replacement generated for the previous update. Spark repeats that entire
> earlier expression in every unchanged-field read. The logical expression can
> therefore grow much faster than the number of requested updates, increasing
> optimizer, expression-binding, and code-generation costs.
>
> ### Example
> {code:java}
> val updated = col("s")
> .withField("nested.a", lit(1))
> .withField("nested.b", lit(2))
> .withField("nested.c", lit(3))
> df.select(updated) {code}
>
> Suppose `s` has the schema
> `struct<nested:struct<value:int>,d:int,e:int,f:int>`. The query changes three
> fields under `nested`; it does not change `d`, `e`, or `f`. Spark
> nevertheless generates reads for those unchanged fields at each replacement
> layer. Those reads repeat the expression generated for the earlier layer, so
> the Catalyst tree grows by far more than the three requested changes.
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