fix RedisBackend.delete_pattern to page the SCAN cursor so all matching keys are deleted

Author: igorbenav

backend/src/infrastructure/cache/backends/redis.py

@@ -106,19 +106,19 @@ async def delete(self, key: str) -> None:
     async def delete_pattern(self, pattern: str) -> None:
         """Delete all keys matching a pattern.
 
+        Pages the ``SCAN`` cursor to completion so every match is removed, not just
+        the first batch. Each batch is deleted as it is scanned.
+
         Args:
             pattern: The pattern to match against keys.
         """
         cursor = 0
-        keys_to_delete = []
-
-        cursor_response, keys = await self.client.scan(cursor=cursor, match=pattern + "*", count=100)
-
-        if keys:
-            keys_to_delete.extend(keys)
-
-        if keys_to_delete:
-            await self.client.delete(*keys_to_delete)
+        while True:
+            cursor, keys = await self.client.scan(cursor=cursor, match=pattern + "*", count=100)
+            if keys:
+                await self.client.delete(*keys)
+            if cursor == 0:
+                break
 
     async def exists(self, key: str) -> bool:
         """Check if a key exists in the cache.

backend/tests/unit/infrastructure/cache/backends/test_redis.py

@@ -73,3 +73,21 @@ async def test_delete_pattern(redis_backend, mock_redis):
     mock_redis.scan.assert_called_once_with(cursor=0, match="test_*", count=100)
 
     mock_redis.delete.assert_called_once_with(b"key1", b"key2", b"key3")
+
+
+@pytest.mark.asyncio
+async def test_delete_pattern_pages_cursor(redis_backend, mock_redis):
+    """delete_pattern pages the SCAN cursor to completion, not just the first batch.
+
+    Regression: the old implementation ran a single SCAN and silently left matches
+    beyond the first window undeleted.
+    """
+    mock_redis.scan.side_effect = [(5, [b"a1", b"a2"]), (0, [b"a3"])]
+
+    await redis_backend.delete_pattern("a")
+
+    assert mock_redis.scan.await_count == 2
+    # the second scan resumes from the cursor the first one returned
+    assert mock_redis.scan.await_args_list[1].kwargs["cursor"] == 5
+    deleted = [k for call in mock_redis.delete.await_args_list for k in call.args]
+    assert deleted == [b"a1", b"a2", b"a3"]