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apache · Nov 23, 2020 · dbc986f · dbc986f
1 parent cef4b55
commit dbc986f
Showing 1 changed file with 5 additions and 0 deletions.
diff --git a/...t/src/main/scala/org/apache/spark/sql/catalyst/expressions/SubExprEvaluationRuntime.scala b/...t/src/main/scala/org/apache/spark/sql/catalyst/expressions/SubExprEvaluationRuntime.scala
@@ -96,6 +96,11 @@ class SubExprEvaluationRuntime(cacheMaxEntries: Int) {
       val proxy = ExpressionProxy(expr, proxyExpressionCurrentId, this)
       proxyExpressionCurrentId += 1
 
+      // We leverage `IdentityHashMap` so we compare expression keys by reference here.
+      // So for example if there are one group of common exprs like Seq(common expr 1,
+      // common expr2, ..., common expr n), we will insert into `proxyMap` some key/value
+      // pairs like Map(common expr 1 -> proxy(common expr 1), ...,
+      // common expr n -> proxy(common expr 1)).
       e.map(proxyMap.put(_, proxy))
     }