ESQL: add a singleton LocalMapper (#138608)

LocalMapper can be instantiated just once.

Author: bpintea

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/enrich/LookupFromIndexService.java

@@ -148,11 +148,7 @@ protected LookupEnrichQueryGenerator queryList(
      * In those cases, it is safe to ignore the plan sent and return null
      */
     private static PhysicalPlan localLookupNodePlanning(PhysicalPlan physicalPlan) {
-        if (physicalPlan instanceof FragmentExec fragmentExec) {
-            LocalMapper localMapper = new LocalMapper();
-            return localMapper.map(fragmentExec.fragment());
-        }
-        return null;
+        return physicalPlan instanceof FragmentExec fragmentExec ? LocalMapper.INSTANCE.map(fragmentExec.fragment()) : null;
     }
 
     @Override

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/planner/PlannerUtils.java

@@ -144,9 +144,8 @@ public static PlanReduction reductionPlan(PhysicalPlan plan) {
             return SimplePlanReduction.NO_REDUCTION;
         }
         final LogicalPlan pipelineBreaker = pipelineBreakers.getFirst();
-        final LocalMapper mapper = new LocalMapper();
         int estimatedRowSize = fragment.estimatedRowSize();
-        return switch (mapper.map(pipelineBreaker)) {
+        return switch (LocalMapper.INSTANCE.map(pipelineBreaker)) {
             case TopNExec topN -> new TopNReduction(EstimatesRowSize.estimateRowSize(estimatedRowSize, topN));
             case AggregateExec aggExec -> getPhysicalPlanReduction(estimatedRowSize, aggExec.withMode(AggregatorMode.INTERMEDIATE));
             case PhysicalPlan p -> getPhysicalPlanReduction(estimatedRowSize, p);
@@ -218,7 +217,6 @@ public static PhysicalPlan localPlan(
         LocalLogicalPlanOptimizer logicalOptimizer,
         LocalPhysicalPlanOptimizer physicalOptimizer
     ) {
-        final LocalMapper localMapper = new LocalMapper();
         var isCoordPlan = new Holder<>(Boolean.TRUE);
         Set<PhysicalPlan> lookupJoinExecRightChildren = plan.collect(LookupJoinExec.class::isInstance)
             .stream()
@@ -234,7 +232,7 @@ public static PhysicalPlan localPlan(
             }
             isCoordPlan.set(Boolean.FALSE);
             LogicalPlan optimizedFragment = logicalOptimizer.localOptimize(f.fragment());
-            PhysicalPlan physicalFragment = localMapper.map(optimizedFragment);
+            PhysicalPlan physicalFragment = LocalMapper.INSTANCE.map(optimizedFragment);
             QueryBuilder filter = f.esFilter();
             if (filter != null) {
                 physicalFragment = physicalFragment.transformUp(

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/planner/mapper/LocalMapper.java

@@ -41,6 +41,10 @@
  */
 public class LocalMapper {
 
+    public static LocalMapper INSTANCE = new LocalMapper();
+
+    private LocalMapper() {}
+
     public PhysicalPlan map(LogicalPlan p) {
 
         if (p instanceof LeafPlan leaf) {

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plugin/LateMaterializationPlanner.java

@@ -133,7 +133,7 @@ public static Optional<ReductionPlan> planReduceDriverTopN(
     }
 
     private static PhysicalPlan toPhysical(LogicalPlan plan, LocalPhysicalOptimizerContext context) {
-        return new InsertFieldExtraction().apply(new ReplaceSourceAttributes().apply(new LocalMapper().map(plan)), context);
+        return new InsertFieldExtraction().apply(new ReplaceSourceAttributes().apply(LocalMapper.INSTANCE.map(plan)), context);
     }
 
     private LateMaterializationPlanner() { /* static class */ }