diff --git a/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java b/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
index fe364c7b7c4..30d7c055470 100644
--- a/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
+++ b/core/src/main/java/org/opensearch/sql/expression/function/PPLFuncImpTable.java
@@ -423,14 +423,10 @@ public void registerExternalOperator(BuiltinFunctionName functionName, SqlOperat
             functionName.name(),
             operator instanceof SqlUserDefinedFunction);
     CalciteFuncSignature signature = new CalciteFuncSignature(functionName.getName(), typeChecker);
-    externalFunctionRegistry.compute(
+    externalFunctionRegistry.put(
         functionName,
-        (name, existingList) -> {
-          List<Pair<CalciteFuncSignature, FunctionImp>> list =
-              existingList == null ? new ArrayList<>() : new ArrayList<>(existingList);
-          list.add(Pair.of(signature, (builder, args) -> builder.makeCall(operator, args)));
-          return list;
-        });
+        List.of(
+            Pair.of(signature, (FunctionImp) (builder, args) -> builder.makeCall(operator, args))));
   }
 
   /**
diff --git a/plugin/src/main/java/org/opensearch/sql/plugin/config/OpenSearchPluginModule.java b/plugin/src/main/java/org/opensearch/sql/plugin/config/OpenSearchPluginModule.java
index 8027301073f..35504dd83c2 100644
--- a/plugin/src/main/java/org/opensearch/sql/plugin/config/OpenSearchPluginModule.java
+++ b/plugin/src/main/java/org/opensearch/sql/plugin/config/OpenSearchPluginModule.java
@@ -58,6 +58,7 @@ public StorageEngine storageEngine(OpenSearchClient client, Settings settings) {
   }
 
   @Provides
+  @Singleton
   public ExecutionEngine executionEngine(
       OpenSearchClient client, ExecutionProtector protector, PlanSerializer planSerializer) {
     return new OpenSearchExecutionEngine(client, protector, planSerializer);