[ZCM] [ZC] 2151/ 1 Request "Random ValueError due to inconsistent ZEO persistent cache code"

[Collector: Zope Bugs, Features, and Patches ...]

Issue #2151 Update (Request) "Random ValueError due to inconsistent ZEO persistent cache code"
 Status Pending, Database/bug critical
To followup, visit:
  http://www.zope.org/Collectors/Zope/2151

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= Request - Entry #1 by chrisw on Jul 17, 2006 7:51 am

Any server running an affected version of ZEO with a persistent client side cache may, at random intervals, die and start emitting tracebacks as below until the .zec files are removed and the app server is restarted:

Traceback (most recent call last):
  File "/usr/local/zope/2.9.3/lib/python/ZEO/zrpc/client.py", line 506, in notify_client
    self.client.notifyConnected(self.conn)
  File "/usr/local/zope/2.9.3/lib/python/ZEO/ClientStorage.py", line 521, in notifyConnected
    self.verify_cache(stub)
  File "/usr/local/zope/2.9.3/lib/python/ZEO/ClientStorage.py", line 589, in verify_cache
    self.invalidateTransaction(*pair)
  File "/usr/local/zope/2.9.3/lib/python/ZEO/ClientStorage.py", line 1114, in invalidateTransaction
    self._cache.setLastTid(tid)
  File "/usr/local/zope/2.9.3/lib/python/ZEO/cache.py", line 151, in setLastTid
    self.fc.settid(tid)
  File "/usr/local/zope/2.9.3/lib/python/ZEO/cache.py", line 1060, in settid
    raise ValueError("new last tid (%s) must be greater than "
ValueError: new last tid (245115767599186653) must be greater than previous one (245115767599186653)

Okay, so why have I logged this as critical?
Well, because no-one seems to understand this code and it's got pretty wide ranging effects. The quick solution is do remove persistent client caches completely, but this would be a big shame as they can be a huge performance win in certain circumstances.

So, does ANYONE want to stump up and make a call on whether the < should be changed to <= or whether this is actualyl a real bgu caused by some other race condition?

Some Zope 2 related details:
http://mail.zope.org/pipermail/zodb-dev/2006-April/010031.html
http://mail.zope.org/pipermail/zodb-dev/2006-June/010157.html

A standalone ZODB example:
http://www.zope.org/Collectors/Zope/2038

A Zope 3 example:
http://mail.zope.org/pipermail/zope3-dev/2006-July/019697.html
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