Github user JoshRosen commented on a diff in the pull request:
https://github.com/apache/spark/pull/13421#discussion_r65273569
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/CodeGenerator.scala
---
@@ -720,15 +721,23 @@ class CodegenContext {
/**
* Register a comment and return the corresponding place holder
*/
- def registerComment(text: String): String = {
- val name = freshName("c")
- val comment = if (text.contains("\n") || text.contains("\r")) {
- text.split("(\r\n)|\r|\n").mkString("/**\n * ", "\n * ", "\n */")
+ def registerComment(text: => String): String = {
+ // By default, disable comments in generated code because computing
the comments themselves can
+ // be extremely expensive in certain cases, such as deeply-nested
expressions which operate over
+ // inputs with wide schemas. For more details on the performance
issues that motivated this
+ // flat, see SPARK-15680.
+ if (SparkEnv.get != null &&
SparkEnv.get.conf.getBoolean("spark.sql.codegen.comments", false)) {
--- End diff --
The problem with using a runtime `SQLConf` (actually a `CatalystConf` (to
avoid a circular dependency)) is that we'd need to thread that configuration
into the implementations of the `CodeGenerator.generate` method and that method
has 60+ call sites, many of which do not have a readily-accessible
configuration instance.
If we had some thread-local mechanism for implicitly obtaining these
configurations then this would be easy, but for now I don't see a simple way to
thread this configuration without changing 20+ files.
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