.

bigfile/file_zodb.py

@@ -178,7 +178,7 @@ will be our future approach after we teach NEO about object deduplication.
 from wendelin.bigfile import BigFile, WRITEOUT_STORE, WRITEOUT_MARKSTORED
 from wendelin import wcfs
 from wendelin.lib.mem import bzero, memcpy
-from wendelin.lib.zodb import deactivate_btree
+from wendelin.lib.zodb import deactivate_btree, zconn_at
 
 from transaction.interfaces import IDataManager, ISynchronizer
 from persistent import Persistent, PickleCache, GHOST
@@ -666,7 +666,7 @@ class ZBigFile(LivePersistent):
             zstor = zconn.db().storage
             zurl = wcfs.zstor_2zurl(zstor)
             wc = wcfs.join(zurl)
-            wconn = wc.connect(zconn.at())
+            wconn = wc.connect(zconn_at(zconn))
             wcfileh = wconn.open(self._p_oid)
 
         fileh = _ZBigFileH(self, wcfileh)

lib/zodb.py

 # Wendelin.bigfile | common ZODB-related helpers
-# Copyright (C) 2014-2015  Nexedi SA and Contributors.
+# Copyright (C) 2014-2019  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -17,12 +17,17 @@
 #
 # See COPYING file for full licensing terms.
 # See https://www.nexedi.com/licensing for rationale and options.
+"""Package wendelin.lib.zodb provides ZODB-related utilitiy functions."""
 
+import ZODB
 from ZODB.FileStorage import FileStorage
 from ZODB import DB
+from ZODB.utils import p64, u64
 from persistent import Persistent
 import gc
 
+import pkg_resources
+
 
 # open db storage by uri
 def dbstoropen(uri):
@@ -105,3 +110,54 @@ def _deactivate_bucket(bucket):
             obj._p_deactivate()
 
     bucket._p_deactivate()
+
+
+# zconn_at returns tid as of which ZODB connection is viewing the database.
+def zconn_at(zconn): # -> tid
+    assert isinstance(zconn, ZODB.Connection.Connection)
+
+    # ZODB5 uses MVCC uniformly
+    if zmajor >= 5:
+        zstor = zconn._storage
+        if isinstance(zstor, ZODB.mvccadapter.MVCCAdapterInstance):
+            # XXX there is race in ZODB itself that leads to data corruption:
+            # https://github.com/zopefoundation/ZODB/issues/290
+            return before2at(zstor._start)
+
+        if isinstance(zstor, ZODB.mvccadapter.HistoricalStorageAdapter):
+            return before2at(zstor._before)
+
+        raise AssertionError("zconn_at: TODO: add support for zstor %r" % zstor)
+
+    raise AssertionError("zconn_at: TODO: add support for ZODB34")
+
+
+# before2at converts tid that specifies database state as "before" into tid that
+# specifies database state as "at".
+def before2at(before): # -> at
+    return p64(u64(before) - 1)
+
+
+# _zversion returns ZODB version object
+def _zversion():
+    dzodb3 = pkg_resources.working_set.find(pkg_resources.Requirement.parse('ZODB3'))
+    dzodb  = pkg_resources.working_set.find(pkg_resources.Requirement.parse('ZODB'))
+    v311   = pkg_resources.parse_version('3.11dev')
+
+    vzodb3 = dzodb3.parsed_version
+    if dzodb3 is not None and vzodb3 >= v311:
+        vzodb = dzodb.parsed_version # ZODB 3.11 just requires latest ZODB & ZEO
+    else:
+        vzodb = vzodb3
+
+    assert vzodb is not None
+    return vzodb
+
+# _zmajor returns major ZODB version.
+def _zmajor():
+    vzodb = _zversion()
+    # XXX hack - packaging.version.Version provides no way to extract major?
+    return int(vzodb.public.split('.')[0])  # 3.11.dev0 -> 3
+
+# zmajor is set to major ZODB version.
+zmajor = _zmajor()