Implemented new bushy layout for blob directories including backwards

compatibility for the old `lawn` layout.

src/CHANGES.txt

@@ -8,6 +8,11 @@ Change History
 New Features
 ------------
 
+- Changed layout strategy for the blob directory to a bushy approach (8 levels
+  deep, at most ~256 entries per directory level, one directory for each
+  blob). Old directories are automatically detected and will be handled with
+  the old strategy.
+
 - Versions are no-longer supported.
 
 - ZEO cache files can be larger than 4G. Note that older ZEO cache

src/ZEO/ClientStorage.py

@@ -855,9 +855,7 @@ class ClientStorage(object):
 
     def _storeBlob_shared(self, oid, serial, data, filename, txn):
         # First, move the blob into the blob directory
-        dir = self.fshelper.getPathForOID(oid)
-        if not os.path.exists(dir):
-            os.mkdir(dir)
+        self.fshelper.getPathForOID(oid, create=True)
         fd, target = self.fshelper.blob_mkstemp(oid, serial)
         os.close(fd)
 
@@ -924,14 +922,7 @@ class ClientStorage(object):
             raise POSException.POSKeyError("No blob file", oid, serial)
 
         # First, we'll create the directory for this oid, if it doesn't exist. 
-        targetpath = self.fshelper.getPathForOID(oid)
-        if not os.path.exists(targetpath):
-            try:
-                os.makedirs(targetpath, 0700)
-            except OSError:
-                # We might have lost a race.  If so, the directory
-                # must exist now
-                assert os.path.exists(targetpath)
+        targetpath = self.fshelper.getPathForOID(oid, create=True)
 
         # OK, it's not here and we (or someone) needs to get it.  We
         # want to avoid getting it multiple times.  We want to avoid
@@ -1118,19 +1109,15 @@ class ClientStorage(object):
                     assert s == tid, (s, tid)
                     self._cache.store(oid, s, None, data)
 
-        
         if self.fshelper is not None:
             blobs = self._tbuf.blobs
             while blobs:
                 oid, blobfilename = blobs.pop()
-                targetpath = self.fshelper.getPathForOID(oid)
-                if not os.path.exists(targetpath):
-                    os.makedirs(targetpath, 0700)
+                targetpath = self.fshelper.getPathForOID(oid, create=True)
                 rename_or_copy_blob(blobfilename,
                           self.fshelper.getBlobFilename(oid, tid),
                           )
 
-                    
         self._tbuf.clear()
 
     def undo(self, trans_id, txn):

src/ZEO/tests/testZEO.py

@@ -515,8 +515,7 @@ class CommonBlobTests:
             self._storage.tpc_abort(t)
             raise
         self.assert_(not os.path.exists(tfname))
-        filename = os.path.join(self.blobdir, oid_repr(oid),
-                                tid_repr(revid) + BLOB_SUFFIX)
+        filename = self._storage.fshelper.getBlobFilename(oid, revid)
         self.assert_(os.path.exists(filename))
         self.assertEqual(somedata, open(filename).read())
 
@@ -631,16 +630,14 @@ class BlobAdaptedFileStorageTests(GenericTests, CommonBlobTests):
                 d2 = somedata.read(8096)
                 self.assertEqual(d1, d2)
 
-        
-        # The file should have been copied to the server:
-        filename = os.path.join(self.blobdir, oid_repr(oid),
-                                tid_repr(revid) + BLOB_SUFFIX)
+        # The file should be in the cache ...
+        filename = self._storage.fshelper.getBlobFilename(oid, revid)
         check_data(filename)
 
-        # It should also be in the cache:
-        filename = os.path.join(self.blob_cache_dir, oid_repr(oid),
-                                tid_repr(revid) + BLOB_SUFFIX)
-        check_data(filename)
+        # ... and on the server
+        server_filename = filename.replace(self.blob_cache_dir, self.blobdir)
+        self.assert_(server_filename.startswith(self.blobdir))
+        check_data(server_filename)
 
         # If we remove it from the cache and call loadBlob, it should
         # come back. We can do this in many threads.  We'll instrument

src/ZODB/blob.py

@@ -15,8 +15,10 @@
 """
 
 import base64
+import binascii
 import logging
 import os
+import re
 import shutil
 import stat
 import sys
@@ -43,6 +45,9 @@ logger = logging.getLogger('ZODB.blob')
 BLOB_SUFFIX = ".blob"
 SAVEPOINT_SUFFIX = ".spb"
 
+LAYOUT_MARKER = '.layout'
+LAYOUTS = {}
+
 valid_modes = 'r', 'w', 'r+', 'a'
 
 # Threading issues:
@@ -292,21 +297,42 @@ class FilesystemHelper:
     # with blobs and storages needn't indirect through this if they
     # want to perform blob storage differently.
 
-    def __init__(self, base_dir):
-        self.base_dir = base_dir
+    def __init__(self, base_dir, layout_name='automatic'):
+        self.base_dir = os.path.normpath(base_dir) + '/'
         self.temp_dir = os.path.join(base_dir, 'tmp')
 
+        if layout_name == 'automatic':
+            layout_name = auto_layout_select(base_dir)
+        if layout_name == 'lawn':
+            log('The `lawn` blob directory layout is deprecated due to '
+                'scalability issues on some file systems, please consider '
+                'migrating to the `bushy` layout.', level=logging.WARN)
+        self.layout_name = layout_name 
+        self.layout = LAYOUTS[layout_name]
+
     def create(self):
         if not os.path.exists(self.base_dir):
             os.makedirs(self.base_dir, 0700)
-            log("Blob cache directory '%s' does not exist. "
-                "Created new directory." % self.base_dir,
-                level=logging.INFO)
+            log("Blob directory '%s' does not exist. "
+                "Created new directory." % self.base_dir)
         if not os.path.exists(self.temp_dir):
             os.makedirs(self.temp_dir, 0700)
             log("Blob temporary directory '%s' does not exist. "
-                "Created new directory." % self.temp_dir,
-                level=logging.INFO)
+                "Created new directory." % self.temp_dir)
+
+        if not os.path.exists(os.path.join(self.base_dir, LAYOUT_MARKER)):
+            layout_marker = open(
+                os.path.join(self.base_dir, LAYOUT_MARKER), 'wb')
+            layout_marker.write(self.layout_name)
+        else:
+            layout_marker = open(
+                os.path.join(self.base_dir, LAYOUT_MARKER), 'rb')
+            layout = layout_marker.read().strip()
+            if layout != self.layout_name:
+                raise ValueError(
+                    "Directory layout `%s` selected for blob directory %s, but "
+                    "marker found for layout `%s`" %
+                    (self.layout_name, self.base_dir, layout))
 
     def isSecure(self, path):
         """Ensure that (POSIX) path mode bits are 0700."""
@@ -317,12 +343,40 @@ class FilesystemHelper:
             log('Blob dir %s has insecure mode setting' % self.base_dir,
                 level=logging.WARNING)
 
-    def getPathForOID(self, oid):
+    def getPathForOID(self, oid, create=False):
         """Given an OID, return the path on the filesystem where
         the blob data relating to that OID is stored.
 
+        If the create flag is given, the path is also created if it didn't
+        exist already.
+
         """
-        return os.path.join(self.base_dir, utils.oid_repr(oid))
+        # OIDs are numbers and sometimes passed around as integers. For our
+        # computations we rely on the 64-bit packed string representation.
+        if isinstance(oid, int):
+            oid = utils.p64(oid)
+
+        path = self.layout.oid_to_path(oid)
+        path = os.path.join(self.base_dir, path)
+
+        if create and not os.path.exists(path):
+            try:
+                os.makedirs(path, 0700)
+            except OSError:
+                # We might have lost a race.  If so, the directory
+                # must exist now
+                assert os.path.exists(targetpath)
+        return path
+
+    def getOIDForPath(self, path):
+        """Given a path, return an OID, if the path is a valid path for an
+        OID. The inverse function to `getPathForOID`.
+
+        Raises ValueError if the path is not valid for an OID.
+
+        """
+        path = path[len(self.base_dir):]
+        return self.layout.path_to_oid(path)
 
     def getBlobFilename(self, oid, tid):
         """Given an oid and a tid, return the full filename of the
@@ -330,6 +384,10 @@ class FilesystemHelper:
 
         """
         oid_path = self.getPathForOID(oid)
+        # TIDs are numbers and sometimes passed around as integers. For our
+        # computations we rely on the 64-bit packed string representation
+        if isinstance(tid, int):
+            tid = utils.p64(tid)
         filename = "%s%s" % (utils.tid_repr(tid), BLOB_SUFFIX)
         return os.path.join(oid_path, filename)
 
@@ -359,10 +417,9 @@ class FilesystemHelper:
         if not filename.endswith(BLOB_SUFFIX):
             return None, None
         path, filename = os.path.split(filename)
-        oid = os.path.split(path)[1]
+        oid = self.getOIDForPath(path)
 
         serial = filename[:-len(BLOB_SUFFIX)]
-        oid = utils.repr_to_oid(oid)
         serial = utils.repr_to_oid(serial)
         return oid, serial 
 
@@ -372,24 +429,104 @@ class FilesystemHelper:
 
         """
         oids = []
-        base_dir = self.base_dir
-        for oidpath in os.listdir(base_dir):
-            for filename in os.listdir(os.path.join(base_dir, oidpath)):
-                blob_path = os.path.join(base_dir, oidpath, filename)
+        for oid, oidpath in self.listOIDs():
+            for filename in os.listdir(oidpath):
+                blob_path = os.path.join(oidpath, filename)
                 oid, serial = self.splitBlobFilename(blob_path)
                 if search_serial == serial:
                     oids.append(oid)
         return oids
 
     def listOIDs(self):
-        """Lists all OIDs and their paths.
-
+        """Iterates over all paths under the base directory that contain blob
+        files.
         """
-        for candidate in os.listdir(self.base_dir):
-            if candidate == 'tmp':
+        for path, dirs, files in os.walk(self.base_dir):
+            try:
+                oid = self.getOIDForPath(path)
+            except ValueError:
                 continue
-            oid = utils.repr_to_oid(candidate)
-            yield oid, self.getPathForOID(oid)
+            yield oid, path
+
+
+def auto_layout_select(path):
+    # A heuristic to look at a path and determine which directory layout to
+    # use. Basically we try to figure out if the directory is either already
+    # used and contains an explicit marker, is unused or used without a
+    # marker.
+    layout_marker = os.path.join(path, LAYOUT_MARKER)
+    if not os.path.exists(path):
+        log('Blob directory %s does not exist. '
+            'Selected `bushy` layout. ' % path)
+        layout = 'bushy'
+    elif len(os.listdir(path)) == 0:
+        log('Blob directory %s is unused and has no layout marker set.'
+            'Selected `bushy` layout. ' % path)
+        layout = 'bushy'
+    elif LAYOUT_MARKER not in os.listdir(path):
+        log('Blob directory %s is used but has no layout marker set.'
+            'Selected `lawn` layout. ' % path)
+        layout = 'lawn'
+    else:
+        layout = open(layout_marker, 'rb').read()
+        layout = layout.strip()
+        log('Blob directory %s has layout marker set.'
+            'Selected `%s` layout. ' % (path, layout))
+    return layout
+
+
+class BushyLayout(object):
+    """A bushy directory layout for blob directories.
+
+    Creates an 8-level directory structure (one level per byte) in
+    little-endian order from the OID of an object.
+
+    """
+
+    blob_path_pattern = r'^' + (r'0x[0-9]{1,2}/*'*8) + r'$'
+    blob_path_pattern = re.compile(blob_path_pattern)
+
+    def oid_to_path(self, oid):
+        directories = []
+        # Create the bushy directory structure with the least significant byte
+        # first
+        for byte in reversed(str(oid)):
+            directories.append('0x%s' % binascii.hexlify(byte))
+        return '/'.join(directories)
+
+    def path_to_oid(self, path):
+        if self.blob_path_pattern.match(path) is None:
+            raise ValueError("Not a valid OID path: %s" % path)
+        # The path always has a leading slash that we need to ignore.
+        path = path.split('/')
+        # The path contains the OID in little endian form but the OID itself
+        # is big endian.
+        path.reverse()
+        # Each path segment stores a byte in hex representation. Turn it into
+        # an int and then get the character for our byte string.
+        oid = ''.join(binascii.unhexlify(byte[2:]) for byte in path)
+        return oid
+
+LAYOUTS['bushy'] = BushyLayout()
+
+
+class LawnLayout(object):
+    """A shallow directory layout for blob directories.
+
+    Creates a single level of directories (one for each oid).
+
+    """
+
+    def oid_to_path(self, oid):
+        return utils.oid_repr(oid)
+
+    def path_to_oid(self, path):
+        try:
+            return utils.repr_to_oid(path)
+        except TypeError:
+            raise ValueError('Not a valid OID path: %s' % path)
+
+LAYOUTS['lawn'] = LawnLayout()
 
 
 class BlobStorage(SpecificationDecoratorBase):
@@ -401,13 +538,13 @@ class BlobStorage(SpecificationDecoratorBase):
     # us to have instance attributes explicitly on the proxy.
     __slots__ = ('fshelper', 'dirty_oids', '_BlobStorage__supportsUndo')
 
-    def __new__(self, base_directory, storage):
+    def __new__(self, base_directory, storage, layout='automatic'):
         return SpecificationDecoratorBase.__new__(self, storage)
 
-    def __init__(self, base_directory, storage):
+    def __init__(self, base_directory, storage, layout='automatic'):
         # XXX Log warning if storage is ClientStorage
         SpecificationDecoratorBase.__init__(self, storage)
-        self.fshelper = FilesystemHelper(base_directory)
+        self.fshelper = FilesystemHelper(base_directory, layout)
         self.fshelper.create()
         self.fshelper.checkSecure()
         self.dirty_oids = []
@@ -438,10 +575,7 @@ class BlobStorage(SpecificationDecoratorBase):
 
         self._lock_acquire()
         try:
-            targetpath = self.fshelper.getPathForOID(oid)
-            if not os.path.exists(targetpath):
-                os.makedirs(targetpath, 0700)
-
+            self.fshelper.getPathForOID(oid, create=True)
             targetname = self.fshelper.getBlobFilename(oid, serial)
             rename_or_copy_blob(blobfilename, targetname)
 
@@ -487,14 +621,12 @@ class BlobStorage(SpecificationDecoratorBase):
         # if they are still needed by attempting to load the revision
         # of that object from the database.  This is maybe the slowest
         # possible way to do this, but it's safe.
-        base_dir = self.fshelper.base_dir
         for oid, oid_path in self.fshelper.listOIDs():
             files = os.listdir(oid_path)
             for filename in files:
                 filepath = os.path.join(oid_path, filename)
                 whatever, serial = self.fshelper.splitBlobFilename(filepath)
                 try:
-                    fn = self.fshelper.getBlobFilename(oid, serial)
                     self.loadSerial(oid, serial)
                 except POSKeyError:
                     remove_committed(filepath)
@@ -504,7 +636,6 @@ class BlobStorage(SpecificationDecoratorBase):
 
     @non_overridable
     def _packNonUndoing(self, packtime, referencesf):
-        base_dir = self.fshelper.base_dir
         for oid, oid_path in self.fshelper.listOIDs():
             exists = True
             try:
@@ -552,15 +683,11 @@ class BlobStorage(SpecificationDecoratorBase):
         """Return the size of the database in bytes."""
         orig_size = getProxiedObject(self).getSize()
         blob_size = 0
-        base_dir = self.fshelper.base_dir
-        for oid in os.listdir(base_dir):
-            sub_dir = os.path.join(base_dir, oid)
-            if not os.path.isdir(sub_dir):
-                continue
-            for serial in os.listdir(sub_dir):
+        for oid, path in self.fshelper.listOIDs():
+            for serial in os.listdir(path):
                 if not serial.endswith(BLOB_SUFFIX):
                     continue
-                file_path = os.path.join(base_dir, oid, serial)
+                file_path = os.path.join(path, serial)
                 blob_size += os.stat(file_path).st_size
 
         return orig_size + blob_size
@@ -583,7 +710,6 @@ class BlobStorage(SpecificationDecoratorBase):
             # we get all the blob oids on the filesystem related to the
             # transaction we want to undo.
             for oid in self.fshelper.getOIDsForSerial(serial_id):
-
                 # we want to find the serial id of the previous revision
                 # of this blob object.
                 load_result = self.loadBefore(oid, serial_id)

src/ZODB/tests/blob_layout.txt

+======================
+Blob directory layouts
+======================
+
+The internal structure of the blob directories is governed by so called
+`layouts`. The current default layout is called `bushy`.
+
+The original blob implementation used a layout that we now call `lawn` and
+which is still available for backwards compatibility.
+
+Layouts implement two methods: one for computing a relative path for an
+OID and one for turning a relative path back into an OID.
+
+Our terminology is roughly the same as used in `DirectoryStorage`.
+
+The `bushy` layout
+==================
+
+The bushy layout splits the OID into the 8 byte parts, reverses them and
+creates one directory level for each part, named by the hexlified
+representation of the byte value. This results in 8 levels of directories, the
+leaf directories being used for the revisions of the blobs and at most 256
+entries per directory level:
+
+>>> from ZODB.blob import BushyLayout
+>>> bushy = BushyLayout()
+>>> bushy.oid_to_path('\x00\x00\x00\x00\x00\x00\x00\x00')
+'0x00/0x00/0x00/0x00/0x00/0x00/0x00/0x00'
+>>> bushy.oid_to_path('\x00\x00\x00\x00\x00\x00\x00\x01')
+'0x01/0x00/0x00/0x00/0x00/0x00/0x00/0x00'
+
+>>> bushy.path_to_oid('0x01/0x00/0x00/0x00/0x00/0x00/0x00/0x00')
+'\x00\x00\x00\x00\x00\x00\x00\x01'
+
+Paths that do not represent an OID will cause a ValueError:
+
+>>> bushy.path_to_oid('tmp')
+Traceback (most recent call last):
+ValueError: Not a valid OID path: tmp
+
+
+The `lawn` layout
+=================
+
+The lawn layout creates on directory for each blob named by the blob's hex
+representation of its OID. This has some limitations on various file systems
+like performance penalties or the inability to store more than a given number
+of blobs at the same time (e.g. 32k on ext3).
+
+>>> from ZODB.blob import LawnLayout
+>>> lawn = LawnLayout()
+>>> lawn.oid_to_path('\x00\x00\x00\x00\x00\x00\x00\x00')
+'0x00'
+>>> lawn.oid_to_path('\x00\x00\x00\x00\x00\x00\x00\x01')
+'0x01'
+
+>>> lawn.path_to_oid('0x01')
+'\x00\x00\x00\x00\x00\x00\x00\x01'
+
+Paths that do not represent an OID will cause a ValueError:
+
+>>> lawn.path_to_oid('tmp')
+Traceback (most recent call last):
+ValueError: Not a valid OID path: tmp
+
+
+Auto-detecting the layout of a directory
+========================================
+
+To allow easier migration, we provide an auto-detection feature that analyses a
+blob directory and decides for a strategy to use. In general it prefers to
+choose the `bushy` layout, except if it determines that the directory has
+already been used to create a lawn structure.
+
+>>> from ZODB.blob import auto_layout_select
+
+1. Non-existing directories will trigger a bushy layout:
+
+>>> import tempfile
+>>> import shutil
+>>> d = tempfile.mkdtemp()
+>>> shutil.rmtree(d)
+>>> auto_layout_select(d)
+'bushy'
+
+2. Empty directories will trigger a bushy layout too:
+
+>>> d = tempfile.mkdtemp()
+>>> auto_layout_select(d)
+'bushy'
+
+3. If the directory contains a marker for the strategy it will be used:
+
+>>> from ZODB.blob import LAYOUT_MARKER
+>>> import os.path
+>>> open(os.path.join(d, LAYOUT_MARKER), 'wb').write('bushy')
+>>> auto_layout_select(d)
+'bushy'
+>>> open(os.path.join(d, LAYOUT_MARKER), 'wb').write('lawn')
+>>> auto_layout_select(d)
+'lawn'
+>>> shutil.rmtree(d)
+
+4. If the directory does not contain a marker but other files, we assume that
+it was created with an earlier version of the blob implementation and uses our
+`lawn` layout:
+
+>>> d = tempfile.mkdtemp()
+>>> open(os.path.join(d, '0x0101'), 'wb').write('foo')
+>>> auto_layout_select(d)
+'lawn'
+>>> shutil.rmtree(d)
+
+
+Directory layout markers
+========================
+
+When the file system helper (FSH) is asked to create the directory structure,
+it will leave a marker with the choosen layout if no marker exists yet:
+
+>>> from ZODB.blob import FilesystemHelper
+>>> d = tempfile.mkdtemp()
+>>> blobs = os.path.join(d, 'blobs')
+>>> fsh = FilesystemHelper(blobs)
+>>> fsh.layout_name
+'bushy'
+>>> fsh.create()
+>>> open(os.path.join(blobs, LAYOUT_MARKER), 'rb').read()
+'bushy'
+
+If the FSH finds a marker, then it verifies whether its content matches the
+strategy that was chosen. It will raise an exception if we try to work with a
+directory that has a different marker than the chosen strategy:
+
+>>> fsh = FilesystemHelper(blobs, 'lawn')
+>>> fsh.layout_name
+'lawn'
+>>> fsh.create() # doctest: +ELLIPSIS
+Traceback (most recent call last):
+ValueError: Directory layout `lawn` selected for blob directory /.../blobs/, but marker found for layout `bushy`
+>>> shutil.rmtree(blobs)
+
+This function interacts with the automatic detection in the way, that an
+unmarked directory will be marked the first time when it is auto-guessed and
+the marker will be used in the future:
+
+>>> import ZODB.FileStorage
+>>> from ZODB.blob import BlobStorage
+>>> datafs = os.path.join(d, 'data.fs')
+>>> base_storage = ZODB.FileStorage.FileStorage(datafs)
+
+>>> os.mkdir(blobs)
+>>> open(os.path.join(blobs, 'foo'), 'wb').write('foo')
+>>> blob_storage = BlobStorage(blobs, base_storage)
+>>> blob_storage.fshelper.layout_name
+'lawn'
+>>> open(os.path.join(blobs, LAYOUT_MARKER), 'rb').read()
+'lawn'
+>>> blob_storage = BlobStorage(blobs, base_storage, layout='bushy') # doctest: +ELLIPSIS
+Traceback (most recent call last):
+ValueError: Directory layout `bushy` selected for blob directory /.../blobs/, but marker found for layout `lawn`
+
+
+>>> shutil.rmtree(d)

src/ZODB/tests/blob_tempdir.txt

@@ -32,7 +32,7 @@ First, we need a datatabase with blob support::
   >>> from ZODB.DB import DB
   >>> from tempfile import mkdtemp
   >>> import os.path
-  >>> base_storage = MappingStorage("test")
+  >>> base_storage = MappingStorage('test')
   >>> blob_dir = mkdtemp()
   >>> blob_storage = BlobStorage(blob_dir, base_storage)
   >>> database = DB(blob_storage)

src/ZODB/tests/blob_transaction.txt

@@ -322,9 +322,9 @@ clean up dirty files:
     >>> base_storage = DummyBaseStorage()
     >>> blob_dir2 = mkdtemp()
     >>> blob_storage2 = BlobStorage(blob_dir2, base_storage)
-    >>> committed_blob_dir = os.path.join(blob_dir2, '0')
-    >>> committed_blob_file = os.path.join(committed_blob_dir, '0.blob')
-    >>> os.mkdir(committed_blob_dir)
+    >>> committed_blob_dir = blob_storage2.fshelper.getPathForOID(0)
+    >>> os.makedirs(committed_blob_dir)
+    >>> committed_blob_file = blob_storage2.fshelper.getBlobFilename(0, 0)
     >>> open(os.path.join(committed_blob_file), 'w').write('foo')
     >>> os.path.exists(committed_blob_file)
     True

src/ZODB/tests/testblob.py

@@ -105,7 +105,6 @@ class BlobUndoTests(unittest.TestCase):
         self.here = os.getcwd()
         os.chdir(self.test_dir)
         self.storagefile = 'Data.fs'
-        os.mkdir('blobs')
         self.blob_dir = 'blobs'
 
     def tearDown(self):
@@ -483,7 +482,7 @@ def loadblob_tmpstore():
     We can access the blob correctly:
 
     >>> tmpstore.loadBlob(blob_oid, tid) # doctest: +ELLIPSIS
-    '.../0x01/0x...blob'
+    '.../0x01/0x00/0x00/0x00/0x00/0x00/0x00/0x00/0x...blob'
 
     Clean up:
 
@@ -503,7 +502,7 @@ def test_suite():
     suite.addTest(doctest.DocFileSuite(
         "blob_basic.txt",  "blob_connection.txt", "blob_transaction.txt",
         "blob_packing.txt", "blob_importexport.txt", "blob_consume.txt",
-        "blob_tempdir.txt",
+        "blob_tempdir.txt", "blob_layout.txt",
         setUp=ZODB.tests.util.setUp,
         tearDown=ZODB.tests.util.tearDown,
         ))