You installed the latest Plone hotfix, 20130618. It includes a DDOS-prevention measure limiting the size of the __cp
cookie data to 8kb (decompressed).
Future Zope versions will also include this fix.
To work around this temporarily your only option is to increase the maximum size default. Doing this will allow other threads use larger cookies as well until you restore the default:
from OFS.CopySupport import _cb_decode
_default_maxsize = _cb_decode.func_defaults[0]
def _increase_maxsize(newsize):
# Patch the maxsize default
_cb_decode.func_defaults = (newsize,)
def _restore_maxsize(newsize):
# Patch the maxsize default
_cb_decode.func_defaults = (_default_maxsize,)
The cookie data consists almost entirely of object paths (absolute paths as tuples) as marshall
dumps, you'll have to estimate a suitable maximum size from that.