Use cached SourceLookup for FieldScript

Signed-off-by: Jay Deng <[email protected]>

Author: jed326

server/src/main/java/org/opensearch/script/FieldScript.java

@@ -78,7 +78,7 @@ public abstract class FieldScript {
     private final LeafSearchLookup leafLookup;
 
     public FieldScript(Map<String, Object> params, SearchLookup lookup, LeafReaderContext leafContext) {
-        this.leafLookup = lookup.getLeafSearchLookup(leafContext);
+        this.leafLookup = lookup.getLeafSearchLookupWithCachedSourceLookup(leafContext);
         params = new HashMap<>(params);
         params.putAll(leafLookup.asMap());
         this.params = new DynamicMap(params, PARAMS_FUNCTIONS);

server/src/main/java/org/opensearch/search/lookup/SearchLookup.java

@@ -165,6 +165,13 @@ public LeafSearchLookup getLeafSearchLookup(LeafReaderContext context) {
         );
     }
 
+    /**
+     * Creates a new LeafSearchLookup using the existing sourceLookup. This is to be used in cases where multiple script instances are processing the same document (non-concurrently).
+     */
+    public LeafSearchLookup getLeafSearchLookupWithCachedSourceLookup(LeafReaderContext context) {
+        return new LeafSearchLookup(context, docMap.getLeafDocLookup(context), sourceLookup, fieldsLookup.getLeafFieldsLookup(context));
+    }
+
     public DocLookup doc() {
         return docMap;
     }