[Andreas Jung]
I have the following script to emulate a long running writing ZEO client
by writing 100MB to a page template:

import transaction

pt = app.foo
while 1:
    data = '*'*100000000
    T = transaction.begin()
    pt.pt_edit(data, 'text/html')
    T.commit()
    print 'done'

This script fails badly during during the first commit() call. Is this a bug
or feature? I am using Zope 2.10.2 on MacOSX Intel.

Probably a bug:

...
suxmac2:~/sandboxes/zeo-test ajung$ bin/zopectl run test.py
2007-02-12 18:18:18 CRITICAL txn.-1610559552 A storage error occurred
during the second phase of the two-phase commit.  Resources may be in an
inconsistent state.
Traceback (most recent call last):
  File "<string>", line 1, in ?
  File "test.py", line 8, in ?
    T.commit()
  File "/opt/zope/2.10.2/lib/python/transaction/_transaction.py", line 395,
in commit
    self._commitResources()
  File "/opt/zope/2.10.2/lib/python/transaction/_transaction.py", line 503,
in _commitResources
    rm.tpc_finish(self)
  File "/opt/zope/2.10.2/lib/python/ZODB/Connection.py", line 696, in
tpc_finish
    self._storage.tpc_finish(transaction, callback)
  File "/opt/zope/2.10.2/lib/python/ZEO/ClientStorage.py", line 955, in
tpc_finish
    self._update_cache(tid)
  File "/opt/zope/2.10.2/lib/python/ZEO/ClientStorage.py", line 980, in
_update_cache
    self._cache.invalidate(oid, version, tid)
  File "/opt/zope/2.10.2/lib/python/ZEO/cache.py", line 375, in invalidate
    assert o is not None
AssertionError

Under the covers "someone" is trying to invalidate a current ZEO cache
entry, and the ZEO cache is complaining because it doesn't believe it
/has/ current data ("assert o is not None").  Best guess for why it
doesn't have it is that it silently refused to add current data to
begin with, because the object pickle was bigger than the size of the
disk file allocated for the ZEO cache.  Offhand I don't recall that
this situation is tested, so it's likely to fail in some way.  One way
to check:  configure the ZEO cache file to be reasonably bigger than
the size of `data = '*'*100000000`.  If the problem goes away then,
that's the cause ;-)
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