From 2406ada16a65b94812f8ca735c5f014a289357cc Mon Sep 17 00:00:00 2001
From: Matthias Wilhelm <matthias.wilhelm@elastic.co>
Date: Thu, 16 Feb 2023 20:03:27 +0100
Subject: [PATCH] Increase flatten performance of SearchSource (#150658)

---
 .../search/search_source/search_source.ts     | 54 ++++++++-----------
 1 file changed, 22 insertions(+), 32 deletions(-)

diff --git a/src/plugins/data/common/search/search_source/search_source.ts b/src/plugins/data/common/search/search_source/search_source.ts
index be7bef0339f3f..0ba2c77c8c016 100644
--- a/src/plugins/data/common/search/search_source/search_source.ts
+++ b/src/plugins/data/common/search/search_source/search_source.ts
@@ -59,17 +59,7 @@
  */
 
 import { setWith } from '@kbn/safer-lodash-set';
-import {
-  difference,
-  isEqual,
-  isFunction,
-  isObject,
-  keyBy,
-  pick,
-  uniqueId,
-  uniqWith,
-  concat,
-} from 'lodash';
+import { difference, isEqual, isFunction, isObject, keyBy, pick, uniqueId, concat } from 'lodash';
 import {
   catchError,
   finalize,
@@ -889,28 +879,28 @@ export class SearchSource {
         // inject the format from the computed fields if one isn't given
         const docvaluesIndex = keyBy(filteredDocvalueFields, 'field');
         const bodyFields = this.getFieldsWithoutSourceFilters(index, body.fields);
-        body.fields = uniqWith(
-          bodyFields.concat(filteredDocvalueFields),
-          (fld1: SearchFieldValue, fld2: SearchFieldValue) => {
-            const field1Name = this.getFieldName(fld1);
-            const field2Name = this.getFieldName(fld2);
-            return field1Name === field2Name;
+
+        const uniqueFieldNames = new Set();
+        const uniqueFields = [];
+        for (const field of bodyFields.concat(filteredDocvalueFields)) {
+          const fieldName = this.getFieldName(field);
+          if (metaFields.includes(fieldName) || uniqueFieldNames.has(fieldName)) {
+            continue;
           }
-        )
-          .filter((fld: SearchFieldValue) => {
-            return !metaFields.includes(this.getFieldName(fld));
-          })
-          .map((fld: SearchFieldValue) => {
-            const fieldName = this.getFieldName(fld);
-            if (Object.keys(docvaluesIndex).includes(fieldName)) {
-              // either provide the field object from computed docvalues,
-              // or merge the user-provided field with the one in docvalues
-              return typeof fld === 'string'
-                ? docvaluesIndex[fld]
-                : this.getFieldFromDocValueFieldsOrIndexPattern(docvaluesIndex, fld, index);
-            }
-            return fld;
-          });
+          uniqueFieldNames.add(fieldName);
+          if (Object.keys(docvaluesIndex).includes(fieldName)) {
+            // either provide the field object from computed docvalues,
+            // or merge the user-provided field with the one in docvalues
+            uniqueFields.push(
+              typeof field === 'string'
+                ? docvaluesIndex[field]
+                : this.getFieldFromDocValueFieldsOrIndexPattern(docvaluesIndex, field, index)
+            );
+          } else {
+            uniqueFields.push(field);
+          }
+        }
+        body.fields = uniqueFields;
       }
     } else {
       body.fields = filteredDocvalueFields;