Refs #30054, #20483 -- Cached SQLite references graph retrieval on sql_flush().

django/db/backends/sqlite3/operations.py

@@ -1,6 +1,8 @@
 import datetime
 import decimal
 import uuid
+from functools import lru_cache
+from itertools import chain
 
 from django.conf import settings
 from django.core.exceptions import FieldError
@@ -11,6 +13,7 @@ from django.db.models.expressions import Col
 from django.utils import timezone
 from django.utils.dateparse import parse_date, parse_datetime, parse_time
 from django.utils.duration import duration_microseconds
+from django.utils.functional import cached_property
 
 
 class DatabaseOperations(BaseDatabaseOperations):
@@ -158,28 +161,36 @@ class DatabaseOperations(BaseDatabaseOperations):
     def no_limit_value(self):
         return -1
 
+    def __references_graph(self, table_name):
+        query = """
+        WITH tables AS (
+            SELECT %s name
+            UNION
+            SELECT sqlite_master.name
+            FROM sqlite_master
+            JOIN tables ON (sql REGEXP %s || tables.name || %s)
+        ) SELECT name FROM tables;
+        """
+        params = (
+            table_name,
+            r'(?i)\s+references\s+("|\')?',
+            r'("|\')?\s*\(',
+        )
+        with self.connection.cursor() as cursor:
+            results = cursor.execute(query, params)
+            return [row[0] for row in results.fetchall()]
+
+    @cached_property
+    def _references_graph(self):
+        # 512 is large enough to fit the ~330 tables (as of this writing) in
+        # Django's test suite.
+        return lru_cache(maxsize=512)(self.__references_graph)
+
     def sql_flush(self, style, tables, sequences, allow_cascade=False):
         if tables and allow_cascade:
             # Simulate TRUNCATE CASCADE by recursively collecting the tables
             # referencing the tables to be flushed.
-            query = """
+            tables = set(chain.from_iterable(self._references_graph(table) for table in tables))
-            WITH tables AS (
-                %s
-                UNION
-                SELECT sqlite_master.name
-                FROM sqlite_master
-                JOIN tables ON (
-                    sql REGEXP %%s || tables.name || %%s
-                )
-            ) SELECT name FROM tables;
-            """ % ' UNION '.join("SELECT '%s' name" % table for table in tables)
-            params = (
-                r'(?i)\s+references\s+("|\')?',
-                r'("|\')?\s*\(',
-            )
-            with self.connection.cursor() as cursor:
-                results = cursor.execute(query, params)
-                tables = [row[0] for row in results.fetchall()]
         sql = ['%s %s %s;' % (
             style.SQL_KEYWORD('DELETE'),
             style.SQL_KEYWORD('FROM'),