From 60242e770882f2ae2dea772350a6de3f767817ad Mon Sep 17 00:00:00 2001
From: Dmitry Dygalo <dmitry@dygalo.dev>
Date: Wed, 15 Dec 2021 21:13:04 +0100
Subject: [PATCH] perf: Cache reference lookups for subschemas

---
 CHANGELOG.rst            |  1 +
 jsonschema/validators.py | 24 +++++++++++++++++-------
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index d10f50f85..507b112d0 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -3,6 +3,7 @@ v4.3.0
 
 * Fix undesired fallback to brute force container uniqueness check on
   certain input types (#893)
+* Cache reference lookups for subschemas (#893)
 * Implement a PEP544 Protocol for validator classes (#890)
 
 v4.2.1
diff --git a/jsonschema/validators.py b/jsonschema/validators.py
index e037c4b9e..46cd8e10a 100644
--- a/jsonschema/validators.py
+++ b/jsonschema/validators.py
@@ -767,15 +767,14 @@ def _finditem(self, schema, key):
                 yield each
             values.extendleft(each.values())
 
-    def resolve(self, ref):
-        """
-        Resolve the given reference.
-        """
-        url = self._urljoin_cache(self.resolution_scope, ref).rstrip("/")
+    @lru_cache()
+    def _find_subschemas(self):
+        return list(self._finditem(self.referrer, "$id"))
 
+    @lru_cache()
+    def _find_in_subschemas(self, url):
         uri, fragment = urldefrag(url)
-
-        for subschema in self._finditem(self.referrer, "$id"):
+        for subschema in self._find_subschemas():
             target_uri = self._urljoin_cache(
                 self.resolution_scope, subschema["$id"],
             )
@@ -783,6 +782,17 @@ def resolve(self, ref):
                 if fragment:
                     subschema = self.resolve_fragment(subschema, fragment)
                 return url, subschema
+        return None
+
+    def resolve(self, ref):
+        """
+        Resolve the given reference.
+        """
+        url = self._urljoin_cache(self.resolution_scope, ref).rstrip("/")
+
+        match = self._find_in_subschemas(url)
+        if match is not None:
+            return match
 
         return url, self._remote_cache(url)