From 9892efacfb46f910f488e02a3e9edf17825a73de Mon Sep 17 00:00:00 2001
From: Rob Richard <robrichard87@gmail.com>
Date: Tue, 20 Oct 2026 14:28:38 -0400
Subject: [PATCH 1/2] add benchmark

---
 benchmark/defer-list-benchmark.js | 81 +++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 benchmark/defer-list-benchmark.js

diff --git a/benchmark/defer-list-benchmark.js b/benchmark/defer-list-benchmark.js
new file mode 100644
index 0000000000..0f2bc506a3
--- /dev/null
+++ b/benchmark/defer-list-benchmark.js
@@ -0,0 +1,81 @@
+import { experimentalExecuteIncrementally } from 'graphql/execution/execute.js';
+import { parse } from 'graphql/language/parser.js';
+import { GraphQLList, GraphQLObjectType } from 'graphql/type/definition.js';
+import {
+  GraphQLDeferDirective,
+  specifiedDirectives,
+} from 'graphql/type/directives.js';
+import { GraphQLString } from 'graphql/type/scalars.js';
+import { GraphQLSchema } from 'graphql/type/schema.js';
+
+const User = new GraphQLObjectType({
+  name: 'User',
+  fields: {
+    name: { type: GraphQLString },
+  },
+});
+
+const users = Array.from({ length: 600 }, (_, index) => ({
+  name: `User ${index + 1}`,
+}));
+
+const schema = new GraphQLSchema({
+  query: new GraphQLObjectType({
+    name: 'Query',
+    fields: {
+      allUsers: {
+        type: new GraphQLList(User),
+        resolve: () => users,
+      },
+    },
+  }),
+  directives: [...specifiedDirectives, GraphQLDeferDirective],
+  assumeValid: true,
+});
+
+const letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
+const labels = [];
+for (let i = 0; i < 31; i++) {
+  // 17.x.x works with `31` set to `26*26`
+  const letter1 = letters[Math.floor(i / 26)];
+  const letter2 = letters[i % 26];
+  labels.push(`${letter1}${letter2}`);
+}
+
+const deferredSpreads = labels
+  .map((label) => `      ...A @defer(label: "${label}")`)
+  .join('\n');
+
+let leafFields = 'name';
+for (let i = 0; i < 20; i++) {
+  leafFields += `\n    ${letters[i]}:name`;
+}
+
+const documentString = `
+  {
+    allUsers {
+${deferredSpreads}
+    }
+  }
+  fragment A on User {
+    ${leafFields}
+  }
+`;
+const document = parse(documentString);
+
+export const benchmark = {
+  name: 'Defer in Large List Benchmark',
+  measure: async () => {
+    const result = await experimentalExecuteIncrementally({
+      schema,
+      document,
+      rootValue: {},
+    });
+    if ('initialResult' in result) {
+      // eslint-disable-next-line no-unused-vars
+      for await (const _subsequentResult of result.subsequentResults) {
+        // noop
+      }
+    }
+  },
+};

From f65ab8a969db415872e2d715fe5a00fe1c260d9a Mon Sep 17 00:00:00 2001
From: Rob Richard <robrichard87@gmail.com>
Date: Tue, 20 Oct 2026 14:54:39 -0400
Subject: [PATCH 2/2] memoize pathToArray to reduce memory for multiple defers
 at the same path

---
 .../incremental/IncrementalPublisher.ts       | 21 ++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/execution/incremental/IncrementalPublisher.ts b/src/execution/incremental/IncrementalPublisher.ts
index 37bcdd083e..3a080ca638 100644
--- a/src/execution/incremental/IncrementalPublisher.ts
+++ b/src/execution/incremental/IncrementalPublisher.ts
@@ -1,4 +1,6 @@
+import { memoize1 } from '../../jsutils/memoize1.ts';
 import type { ObjMap } from '../../jsutils/ObjMap.ts';
+import type { Path } from '../../jsutils/Path.ts';
 import { pathToArray } from '../../jsutils/Path.ts';
 
 import { ensureGraphQLError } from '../../error/ensureGraphQLError.ts';
@@ -36,9 +38,13 @@ export class IncrementalPublisher {
   private _ids: Map<DeliveryGroup | ItemStream, string>;
   private _nextId: number;
 
+  private _cachedPathToArray: (path: Path) => Array<string | number>;
   constructor() {
     this._ids = new Map();
     this._nextId = 0;
+    // Paths are shared by every defer label at one response position, so the
+    // flattened array is built once per Path instead of once per label.
+    this._cachedPathToArray = memoize1((path: Path) => pathToArray(path));
   }
 
   buildResponse(
@@ -88,6 +94,13 @@ export class IncrementalPublisher {
     };
   }
 
+  private _pathToArray(path: Path | undefined): Array<string | number> {
+    if (path == null) {
+      return [];
+    }
+    return this._cachedPathToArray(path);
+  }
+
   private _ensureId(
     deferredFragmentOrStream: DeliveryGroup | ItemStream,
   ): string {
@@ -110,7 +123,7 @@ export class IncrementalPublisher {
         const id = this._ensureId(node);
         const pendingResult: PendingResult = {
           id,
-          path: pathToArray(node.path),
+          path: this._pathToArray(node.path),
         };
         if (node.label !== undefined) {
           pendingResult.label = node.label;
@@ -267,7 +280,9 @@ export class IncrementalPublisher {
     initialDeferredFragmentRecord: DeliveryGroup,
     executionGroupValue: ExecutionGroupValue,
   ): { bestId: string; subPath: ReadonlyArray<string | number> | undefined } {
-    let maxLength = pathToArray(initialDeferredFragmentRecord.path).length;
+    let maxLength = this._pathToArray(
+      initialDeferredFragmentRecord.path,
+    ).length;
     let bestId = initialId;
 
     for (const deliveryGroup of executionGroupValue.deliveryGroups) {
@@ -279,7 +294,7 @@ export class IncrementalPublisher {
       if (id === undefined) {
         continue;
       }
-      const path = pathToArray(deliveryGroup.path);
+      const path = this._pathToArray(deliveryGroup.path);
       const length = path.length;
       if (length > maxLength) {
         maxLength = length;