Handle DB creation race condition

Till now if a race occurs on a request to a DB when it is
first created, the loosing party die with 500...
... and an error stating a race is in the log file.

Both removed by simply accepting the fact that the DB is in fact
created by someone else - just less work for us to do... ;)

Fixes Bug #1051998

Change-Id: I8e29bf362edf2b1a84f9bffa39c04d5b3dc241b2

swift/account/server.py

@@ -113,8 +113,11 @@ def PUT(self, req):
                 broker.pending_timeout = 3
             if account.startswith(self.auto_create_account_prefix) and \
                     not os.path.exists(broker.db_file):
-                broker.initialize(normalize_timestamp(
-                    req.headers.get('x-timestamp') or time.time()))
+                try:
+                    broker.initialize(normalize_timestamp(
+                        req.headers.get('x-timestamp') or time.time()))
+                except swift.common.db.DatabaseAlreadyExists:
+                    pass
             if req.headers.get('x-account-override-deleted', 'no').lower() != \
                     'yes' and broker.is_deleted():
                 return HTTPNotFound(request=req)
@@ -130,8 +133,11 @@ def PUT(self, req):
         else:   # put account
             timestamp = normalize_timestamp(req.headers['x-timestamp'])
             if not os.path.exists(broker.db_file):
-                broker.initialize(timestamp)
-                created = True
+                try:
+                    broker.initialize(timestamp)
+                    created = True
+                except swift.common.db.DatabaseAlreadyExists:
+                    pass
             elif broker.is_status_deleted():
                 return HTTPForbidden(request=req, body='Recently deleted')
             else:

swift/common/db.py

@@ -70,6 +70,16 @@ def __str__(self):
             self.path, self.timeout, self.msg)
 
 
+class DatabaseAlreadyExists(sqlite3.DatabaseError):
+    """More friendly error messages for DB Errors."""
+
+    def __init__(self, path):
+        self.path = path
+
+    def __str__(self):
+        return 'DB %s already exists' % self.path
+
+
 class GreenDBConnection(sqlite3.Connection):
     """SQLite DB Connection handler that plays well with eventlet."""
 
@@ -247,9 +257,7 @@ def initialize(self, put_timestamp=None):
                 if os.path.exists(self.db_file):
                     # It's as if there was a "condition" where different parts
                     # of the system were "racing" each other.
-                    raise DatabaseConnectionError(
-                        self.db_file,
-                        'DB created by someone else while working?')
+                    raise DatabaseAlreadyExists(self.db_file)
                 renamer(tmp_db_file, self.db_file)
             self.conn = get_db_connection(self.db_file, self.timeout)
         else:

swift/container/server.py

@@ -198,8 +198,11 @@ def DELETE(self, req):
         broker = self._get_container_broker(drive, part, account, container)
         if account.startswith(self.auto_create_account_prefix) and obj and \
                 not os.path.exists(broker.db_file):
-            broker.initialize(normalize_timestamp(
-                req.headers.get('x-timestamp') or time.time()))
+            try:
+                broker.initialize(normalize_timestamp(
+                    req.headers.get('x-timestamp') or time.time()))
+            except swift.common.db.DatabaseAlreadyExists:
+                pass
         if not os.path.exists(broker.db_file):
             return HTTPNotFound()
         if obj:     # delete object
@@ -247,7 +250,10 @@ def PUT(self, req):
         if obj:     # put container object
             if account.startswith(self.auto_create_account_prefix) and \
                     not os.path.exists(broker.db_file):
-                broker.initialize(timestamp)
+                try:
+                    broker.initialize(timestamp)
+                except swift.common.db.DatabaseAlreadyExists:
+                    pass
             if not os.path.exists(broker.db_file):
                 return HTTPNotFound()
             broker.put_object(obj, timestamp, int(req.headers['x-size']),
@@ -256,8 +262,11 @@ def PUT(self, req):
             return HTTPCreated(request=req)
         else:   # put container
             if not os.path.exists(broker.db_file):
-                broker.initialize(timestamp)
-                created = True
+                try:
+                    broker.initialize(timestamp)
+                    created = True
+                except swift.common.db.DatabaseAlreadyExists:
+                    pass
             else:
                 created = broker.is_deleted()
                 broker.update_put_timestamp(timestamp)

test/unit/common/test_db.py

@@ -25,6 +25,7 @@
 
 import simplejson
 import sqlite3
+from mock import patch
 
 import swift.common.db
 from swift.common.db import AccountBroker, chexor, ContainerBroker, \
@@ -99,6 +100,7 @@ def setUp(self):
     def test_DB_PREALLOCATION_setting(self):
         u = uuid4().hex
         b = DatabaseBroker(u)
+        swift.common.db.DB_PREALLOCATION = False
         b._preallocate()
         swift.common.db.DB_PREALLOCATION = True
         self.assertRaises(OSError, b._preallocate)
@@ -147,6 +149,15 @@ def stub(*args, **kwargs):
             conn.execute('SELECT * FROM outgoing_sync')
             conn.execute('SELECT * FROM incoming_sync')
 
+        def my_exists(*a, **kw):
+            return True
+
+        with patch('os.path.exists', my_exists):
+            broker = DatabaseBroker(os.path.join(self.testdir, '1.db'))
+            broker._initialize = stub
+            self.assertRaises(swift.common.db.DatabaseAlreadyExists,
+                broker.initialize, normalize_timestamp('1'))
+
     def test_delete_db(self):
         def init_stub(conn, put_timestamp):
             conn.execute('CREATE TABLE test (one TEXT)')