pithos: enforce transaction isolation level

Refs: #3582 #3585

snf-pithos-backend/pithos/backends/lib/sqlalchemy/dbwrapper.py

@@ -33,8 +33,7 @@
 
 from sqlalchemy import create_engine
 #from sqlalchemy.event import listen
-from sqlalchemy.engine import Engine
-from sqlalchemy.pool import NullPool, QueuePool
+from sqlalchemy.pool import NullPool
 from sqlalchemy.interfaces import PoolListener
 
 
@@ -45,16 +44,20 @@ class DBWrapper(object):
         if db.startswith('sqlite://'):
             class ForeignKeysListener(PoolListener):
                 def connect(self, dbapi_con, con_record):
-                    db_cursor = dbapi_con.execute('pragma foreign_keys=ON;')
-                    db_cursor = dbapi_con.execute(
-                        'pragma case_sensitive_like=ON;')
-            self.engine = create_engine(db, connect_args={'check_same_thread': False}, poolclass=NullPool, listeners=[ForeignKeysListener()])
+                    dbapi_con.execute('pragma foreign_keys=ON;')
+                    dbapi_con.execute('pragma case_sensitive_like=ON;')
+            self.engine = create_engine(
+                db, connect_args={'check_same_thread': False},
+                poolclass=NullPool, listeners=[ForeignKeysListener()],
+                isolation_level='SERIALIZABLE')
         #elif db.startswith('mysql://'):
         #    db = '%s?charset=utf8&use_unicode=0' %db
         #    self.engine = create_engine(db, convert_unicode=True)
         else:
             #self.engine = create_engine(db, pool_size=0, max_overflow=-1)
-            self.engine = create_engine(db, poolclass=NullPool)
+            self.engine = create_engine(
+                db, poolclass=NullPool, isolation_level='READ COMMITTED'
+        )
         self.engine.echo = False
         self.engine.echo_pool = False
         self.conn = self.engine.connect()

snf-pithos-backend/pithos/backends/lib/sqlalchemy/node.py

@@ -234,14 +234,14 @@ class Node(DBWorker):
         r.close()
         return inserted_primary_key
 
-    def node_lookup(self, path):
+    def node_lookup(self, path, for_update=False):
         """Lookup the current node of the given path.
            Return None if the path is not found.
         """
 
         # Use LIKE for comparison to avoid MySQL problems with trailing spaces.
         s = select([self.nodes.c.node], self.nodes.c.path.like(
-            self.escape_like(path), escape=ESCAPE_CHAR))
+            self.escape_like(path), escape=ESCAPE_CHAR), for_update=for_update)
         r = self.conn.execute(s)
         row = r.fetchone()
         r.close()

snf-pithos-backend/pithos/backends/lib/sqlite/node.py

@@ -203,9 +203,11 @@ class Node(DBWorker):
         props = (parent, path)
         return self.execute(q, props).lastrowid
 
-    def node_lookup(self, path):
+    def node_lookup(self, path, **kwargs):
         """Lookup the current node of the given path.
            Return None if the path is not found.
+
+           kwargs is not used: it is passed for conformance
         """
 
         q = "select node from nodes where path = ?"

snf-pithos-backend/pithos/backends/modular.py

@@ -1217,7 +1217,7 @@ class ModularBackend(BaseBackend):
 
     def _lookup_container(self, account, container):
         path = '/'.join((account, container))
-        node = self.node.node_lookup(path)
+        node = self.node.node_lookup(path, for_update=True)
         if node is None:
             raise ItemNotExists('Container does not exist')
         return path, node