account-broker: add resilient path property with lazy cache

Add a path property for AccountBroker and use lazy, resilient
_populate_instance_cache(). Use None attrs as flags, avoid broad
try/except in path, and retry if cache population fails.

Change-Id: Ic7c2aa878caf039b29abb900b4f491130be3d8a8
Signed-off-by: ashnair <ashnair@nvidia.com>

swift/account/backend.py

@@ -224,6 +224,18 @@ class AccountBroker(DatabaseBroker):
                 record['bytes_used'], record['deleted'],
                 record['storage_policy_index'])
 
+    @property
+    def path(self):
+        """
+        Logical namespace path used for logging.
+
+        For ContainerBroker this is "<account>/<container>";
+        for AccountBroker we return just "<account>".
+        """
+        if self.account is None:
+            self._populate_instance_cache()
+        return self.account or ''
+
     def put_container(self, name, put_timestamp, delete_timestamp,
                       object_count, bytes_used, storage_policy_index):
         """
@@ -336,7 +348,7 @@ class AccountBroker(DatabaseBroker):
 
     def get_info(self):
         """
-        Get global data for the account.
+        Return a dict with account name for this broker.
 
         :returns: dict with keys: account, created_at, put_timestamp,
                   delete_timestamp, status_changed_at, container_count,
@@ -344,12 +356,14 @@ class AccountBroker(DatabaseBroker):
         """
         self._commit_puts_stale_ok()
         with self.get() as conn:
-            return dict(conn.execute('''
+            data = dict(conn.execute('''
                 SELECT account, created_at,  put_timestamp, delete_timestamp,
                        status_changed_at, container_count, object_count,
                        bytes_used, hash, id
                 FROM account_stat
             ''').fetchone())
+        self.account = data.get('account')
+        return data
 
     def list_containers_iter(self, limit, marker, end_marker, prefix,
                              delimiter, reverse=False, allow_reserved=False):
@@ -639,3 +653,15 @@ class AccountBroker(DatabaseBroker):
             ALTER TABLE container
             ADD COLUMN storage_policy_index INTEGER DEFAULT 0;
         ''' + POLICY_STAT_TRIGGER_SCRIPT)
+
+    def _populate_instance_cache(self):
+        """
+        Lazily hydrate instance attributes used for logging and other
+        read-mostly flows. Use `self.account is None` as the only
+        indicator that we haven't populated yet.
+
+        On failure, we leave `self.account` as-is (likely None) so that
+        a future caller can try again.
+        """
+        if self.account is None:
+            self.get_info()

test/unit/account/test_backend.py

@@ -14,7 +14,6 @@
 # limitations under the License.
 
 """ Tests for swift.account.backend """
-
 from collections import defaultdict
 import json
 import pickle
@@ -1216,6 +1215,25 @@ class TestAccountBrokerBeforeMetadata(TestAccountBroker):
                 exc = err
         self.assertIn('no such column: metadata', str(exc))
 
+    def test_path_lazy_populates_from_db(self):
+        b = AccountBroker(self.get_db_path(), account=None)
+        self.assertIsNone(getattr(b, 'account', None))
+        called = {'n': 0}
+
+        def stub_populate(self, conn=None):
+            called['n'] += 1
+            self.account = 'a'
+
+        with mock.patch.object(AccountBroker, '_populate_instance_cache',
+                               stub_populate):
+            self.assertEqual('a', b.path)
+            self.assertEqual('a', b.account)
+            self.assertEqual(1, called['n'])
+
+    def test_path_best_effort_when_partial_attrs(self):
+        b = AccountBroker(self.get_db_path(), account='a')
+        self.assertEqual('a', b.path)
+
     def tearDown(self):
         AccountBroker.create_account_stat_table = \
             self._imported_create_account_stat_table