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https://issues.apache.org/jira/browse/SPARK-17728?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15552708#comment-15552708
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Jacob Eisinger commented on SPARK-17728:
----------------------------------------
[~hvanhovell], thanks for looking into this! Unless you can think of a better
way to ensure the UDF doesn't get executed multiple times, we are going to go
with your workaround of:
{code}
val exploded = as
.withColumn("structured_information", explode(array(fUdf('a))))
.withColumn("plus_one", 'structured_information("plusOne"))
.withColumn("squared", 'structured_information("squared"))
{code}
{code}
exploded2.explain
== Physical Plan ==
*Project [a#10, structured_information#159, structured_information#159.plusOne
AS plus_one#161, structured_information#159.squared AS squared#166]
+- Generate explode(array(if (isnull(a#10)) null else UDF(a#10))), true, false,
[a#10, structured_information#159]
+- *BatchedScan parquet [a#10] Format: ParquetFormat, InputPaths:
file:/tmp/as.parquet, PushedFilters: [], ReadSchema: struct<a:int>
{code}
I reckon it might impact GC a bit with the creation of the extra arrays ---
but, that sure beats the cost of running those expensive UDFs! Thanks again
for the excellent explanations!
> UDFs are run too many times
> ---------------------------
>
> Key: SPARK-17728
> URL: https://issues.apache.org/jira/browse/SPARK-17728
> Project: Spark
> Issue Type: Bug
> Components: Spark Core
> Affects Versions: 2.0.0
> Environment: Databricks Cloud / Spark 2.0.0
> Reporter: Jacob Eisinger
> Priority: Minor
> Attachments: over_optimized_udf.html
>
>
> h3. Background
> Llonger running processes that might run analytics or contact external
> services from UDFs. The response might not just be a field, but instead a
> structure of information. When attempting to break out this information, it
> is critical that query is optimized correctly.
> h3. Steps to Reproduce
> # Create some sample data.
> # Create a UDF that returns a multiple attributes.
> # Run UDF over some data.
> # Create new columns from the multiple attributes.
> # Observe run time.
> h3. Actual Results
> The UDF is executed *multiple times* _per row._
> h3. Expected Results
> The UDF should only be executed *once* _per row._
> h3. Workaround
> Cache the Dataset after UDF execution.
> h3. Details
> For code and more details, see [^over_optimized_udf.html]
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