Commit 1f866c00 authored by Kirill Smelkov's avatar Kirill Smelkov

lib/zodb: Teach zconn_at to work on ZODB4

In 3bd82127 (lib/zodb: Add zconn_at draft (ZODB5 only)) we added
zconn_at function to find out as of which state a ZODB connection is
viewing the database. That was ZODB5-only however.

Let's add support for ZODB4 now - by requiring ZODB4-wc2 - a version of
ZODB4 with MVCC backported from ZODB5: ZODB!1

This makes wendelin.core to work on either ZODB5 or ZODB4-wc2, but not
plain ZODB4. However as zconn_at will be used only for WCFS-integration,
non-wcfs mode will continue to work on all ZODB5, ZODB4-wc2 and plain
ZODB4.

ZBigFile + WCFS client integration will use zconn_at to open WCFS
connection that corresponds to ZODB connection.

Preliminary history:

kirr/wendelin.core@1c3b7750    X zconn_at for ZODB4
parent 1dba3a9a
......@@ -17,7 +17,7 @@
#
# See COPYING file for full licensing terms.
# See https://www.nexedi.com/licensing for rationale and options.
from wendelin.lib.zodb import LivePersistent, deactivate_btree, dbclose, zconn_at, zstor_2zurl, zmajor
from wendelin.lib.zodb import LivePersistent, deactivate_btree, dbclose, zconn_at, zstor_2zurl
from wendelin.lib.testing import getTestDB
from wendelin.lib import testing
from persistent import Persistent, UPTODATE, GHOST, CHANGED
......@@ -236,7 +236,6 @@ def test_deactivate_btree():
# verify that zconn_at gives correct answer.
@xfail(zmajor < 5, reason="zconn_at is TODO for ZODB4")
@func
def test_zconn_at():
stor = testdb.getZODBStorage()
......
......@@ -156,18 +156,18 @@ def zconn_at(zconn): # -> tid
# ZODB4
#
# Connection:
# .before !None for historic connections
#
# ._txn_time - if !None - set to tid of _next_ transaction
# XXX set to None initially - what to do?
#
# # XXX do something like that ZODB5 is doing:
# zconn._start = zconn._storage.lastTransaction() + 1
# # XXX _and_ check out queued invalidations
# We rely on our patch in 4-nxd branch that reworks ZODB.Connection to
# implement MVCC via always calling loadBefore(zconn._txn_time) to load objects.
elif zmajor == 4:
raise AssertionError("zconn_at: TODO: add support for ZODB4")
assert 'conn:MVCC-via-loadBefore-only' in ZODB.nxd_patches, \
"https://lab.nexedi.com/nexedi/ZODB/merge_requests/1"
if zconn._mvcc_storage:
raise NotImplementedError("Connection.at for IMVCCStorage is not implemented")
if zconn.before is not None:
return before2at(zconn.before) # historical connection
else:
return before2at(zconn._txn_time) # "current" connection
# ZODB3
else:
......
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