Avoid creating exceptions for warnings

Author: ivancea

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/operator/Warnings.java

@@ -89,12 +89,23 @@ private Warnings(int lineNumber, int columnNumber, String sourceText, String fir
     }
 
     public void registerException(Exception exception) {
+        registerException(exception.getClass(), exception.getMessage());
+    }
+
+    /**
+     * Register an exception to be included in the warnings.
+     * <p>
+     *     This overload avoids the need to instantiate the exception, which can be expensive.
+     *     Instead, it asks only the required pieces to build the warning.
+     * </p>
+     */
+    public void registerException(Class<? extends Exception> exceptionClass, String message) {
         if (addedWarnings < MAX_ADDED_WARNINGS) {
             if (addedWarnings == 0) {
                 addWarning(first);
             }
             // location needs to be added to the exception too, since the headers are deduplicated
-            addWarning(location + exception.getClass().getName() + ": " + exception.getMessage());
+            addWarning(location + exceptionClass.getName() + ": " + message);
             addedWarnings++;
         }
     }

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/querydsl/query/SingleValueMatchQuery.java

@@ -48,12 +48,12 @@ public final class SingleValueMatchQuery extends Query {
     private static final int MULTI_VALUE_MATCH_COST = 1000;
     private final IndexFieldData<?> fieldData;
     private final Warnings warnings;
-    private final IllegalArgumentException multiValueException;
+    private final String multiValueExceptionMessage;
 
     public SingleValueMatchQuery(IndexFieldData<?> fieldData, Warnings warnings, String multiValueExceptionMessage) {
         this.fieldData = fieldData;
         this.warnings = warnings;
-        this.multiValueException = new IllegalArgumentException(multiValueExceptionMessage);
+        this.multiValueExceptionMessage = multiValueExceptionMessage;
     }
 
     @Override
@@ -122,7 +122,7 @@ private ScorerSupplier scorerSupplier(
                         return false;
                     }
                     if (sortedNumerics.docValueCount() != 1) {
-                        warnings.registerException(multiValueException);
+                        registerMultiValueException();
                         return false;
                     }
                     return true;
@@ -157,7 +157,7 @@ private ScorerSupplier scorerSupplier(
                         return false;
                     }
                     if (sortedSetDocValues.docValueCount() != 1) {
-                        warnings.registerException(multiValueException);
+                        registerMultiValueException();
                         return false;
                     }
                     return true;
@@ -186,7 +186,7 @@ private ScorerSupplier scorerSupplier(
                         return false;
                     }
                     if (sortedBinaryDocValues.docValueCount() != 1) {
-                        warnings.registerException(multiValueException);
+                        registerMultiValueException();
                         return false;
                     }
                     return true;
@@ -266,6 +266,10 @@ public long cost() {
         }
     }
 
+    private void registerMultiValueException() {
+        warnings.registerException(IllegalArgumentException.class, multiValueExceptionMessage);
+    }
+
     private static class PredicateScorerSupplier extends ScorerSupplier {
         private final float score;
         private final ScoreMode scoreMode;