From 117c7cf9f3ea5eca39e84fbcb92d417760bc01ba Mon Sep 17 00:00:00 2001
From: James Garbutt <43081j@users.noreply.github.com>
Date: Sun, 19 Jul 2026 16:28:42 +0100
Subject: [PATCH] perf: special case arrays in partialMatchKey
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This does 2 things:

1. If the values being compared are both arrays, iterate through them
   directly
2. Use a `for...of` instead of allocating an arrow function per
   recursive call

The results:

| Task name | Latency avg (ns) | Latency med (ns) | Throughput avg (ops/s) | Throughput med (ops/s) | Samples |
| -- | -- | -- | -- | -- | -- |
| 'partialMatchKey dev' | '38.21 ± 0.16%' | '42.00 ± 0.00' | '24035274 ± 0.00%' | '23809524 ± 1' | 13086480 |
| 'partialMatchKey prod' | '102.05 ± 0.52%' | '84.00 ± 1.00' | '10289814 ± 0.02%' | '11904762 ± 143431' | 4899508 |
---
 .changeset/humble-tips-try.md    |  5 +++++
 packages/query-core/src/utils.ts | 17 ++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/humble-tips-try.md

diff --git a/.changeset/humble-tips-try.md b/.changeset/humble-tips-try.md
new file mode 100644
index 00000000000..ecc28ea0aaa
--- /dev/null
+++ b/.changeset/humble-tips-try.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/query-core': patch
+---
+
+Improve `partialMatchKey` performance in query-core.
diff --git a/packages/query-core/src/utils.ts b/packages/query-core/src/utils.ts
index b97b2cc5a33..f442ab86fdc 100644
--- a/packages/query-core/src/utils.ts
+++ b/packages/query-core/src/utils.ts
@@ -256,7 +256,22 @@ export function partialMatchKey(a: any, b: any): boolean {
   }
 
   if (a && b && typeof a === 'object' && typeof b === 'object') {
-    return Object.keys(b).every((key) => partialMatchKey(a[key], b[key]))
+    if (Array.isArray(a) && Array.isArray(b)) {
+      for (let i = 0; i < b.length; i++) {
+        if (!partialMatchKey(a[i], b[i])) {
+          return false
+        }
+      }
+      return true
+    }
+
+    const bKeys = Object.keys(b)
+    for (const key of bKeys) {
+      if (!partialMatchKey(a[key], b[key])) {
+        return false
+      }
+    }
+    return true
   }
 
   return false