[GitHub] [spark] maropu commented on a change in pull request #24028: [SPARK-26917][SQL] Further reduce locks in CacheManager

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maropu commented on a change in pull request #24028: [SPARK-26917][SQL] Further reduce locks in CacheManager
URL: https://github.com/apache/spark/pull/24028#discussion_r264019535
 
 

 ##########
 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/CacheManager.scala
 ##########
 @@ -144,16 +144,10 @@ class CacheManager extends Logging {
       } else {
         _.sameResult(plan)
       }
-    val plansToUncache = mutable.Buffer[CachedData]()
-    readLock {
-      val it = cachedData.iterator()
-      while (it.hasNext) {
-        val cd = it.next()
-        if (shouldRemove(cd.plan)) {
-          plansToUncache += cd
-        }
-      }
+    val cachedDataCopy = readLock {
+      cachedData.asScala.clone()
     }
+    val plansToUncache = cachedDataCopy.filter(cd => shouldRemove(cd.plan))
 
 Review comment:
   It seems we always use `whole` loops when performance should be a concern:
   https://github.com/databricks/scala-style-guide#traversal-and-zipwithindex
   No actual performance impact between the two pattens on your heavy workload?

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