[ZODB-Dev] ZEO cache bug? (again)

[Jim Fulton]

On Jul 31, 2006, at 3:55 PM, Jim Fulton wrote:

>
> On May 31, 2006, at 4:03 AM, Chris Withers wrote:
>
>> Hi All,
>>
>> I mentioned this before:
>>
>>   File "C:\Zope\2.9.2\lib\python\ZEO\cache.py", line 151, in  
>> setLastTid
>>     self.fc.settid(tid)
>>   File "C:\Zope\2.9.2\lib\python\ZEO\cache.py", line 1060, in settid
>>     raise ValueError("new last tid (%s) must be greater than "
>> ValueError: new last tid (244828509247418982) must be greater than  
>> previous one (244828509247418982)
>>
>> I see this intermittently...
>
> Hey Chris,
>
> I have a few questions for you wrt this.  When you see this:
>
> - Are there multiple ZEO clients involved?
>
> - If you shutdown the server and client and restart them, does the
>   problem persist?

I'll note that I have been able to provoke the error message, but,  
for me at least, the result was non-fatal.  The error occurs during  
cache verification and causes the connection to fail. The connection  
thread keeps running and tries again.  The error, as provoked by me,  
arises from a race condition in a situation in which one client is  
connecting while other clients are writing.  Unless other clients are  
writing furiously, I don't see why this would prevent a client from  
connecting eventually.  This makes me wonder if, perhaps, I'm not  
seeing the same error that you are reporting. OTOH, I haven't been  
able to think of another situation in which this symptom could occur.

If you are seeing this error a lot, I suggest setting invalidation- 
queue-size to 1 on your storage server (and restarting of course). It  
would be interesting to know if this setting makes the error go away.

I'd like to get some more info on this to try to chase it down.

I'm taking a few days off.  I'll look for you on IRC when I get back.

Jim

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