[ZODB-Dev] Re: "Time travel" conflict errors in Zope

[Malcolm Cleaton]

On Mon, 20 Dec 2004 11:49:10 +0100, Thomas Guettler wrote:
> Am Montag, 20. Dezember 2004 11:29 schrieb Malcolm Cleaton:
>> Hi.
>>
>> One of our servers, after the disk filled up, started showing some "time
>> travel" conflict errors.
> 
> Hi,
> 
> ZODB does not like it, if your system clock goes backward. 

Thanks Thomas. That's interesting and useful, but I'm not sure it's the
problem in this case.

One of my colleagues has managed to find a copy of the traceback (which
seemed to only be displayed, and not show up in the log):

An error was encountered while publishing this resource.

*ZODB.POSException.ConflictError*

Sorry, a site error occurred.

Traceback (innermost last):

    * Module ZPublisher.Publish, line 175, in publish_module_standard
    * Module ZPublisher.Publish, line 149, in publish
    * Module ZPublisher.Publish, line 149, in publish
    * Module ZPublisher.Publish, line 149, in publish
    * Module ZPublisher.Publish, line 139, in publish
    * Module Zope.App.startup, line 163, in zpublisher_exception_hook
    * Module ZPublisher.Publish, line 107, in publish
    * Module Zope.App.startup, line 222, in commit
    * Module ZODB.Transaction, line 252, in commit
    * Module ZODB.Connection, line 737, in tpc_vote
    * Module ZEO.ClientStorage, line 841, in tpc_vote
    * Module ZEO.ClientStorage, line 825, in _check_serials

ConflictError: database conflict error (oid 0x10fd16, serial this txn 
started with 0x0359debd2d2ababb 2004-12-14 14:53:10.585995, serial 
currently committed 0x0359defb79b34a88 2004-12-14 15:55:28.523521)


This traceback was seen late in the afternoon - after 16:00 - and the
server clock was correct (enough) at the time. So, it looks like the
timestamp on the committed transaction is reasonable, and the mystery is
why the "serial this txn started with" is many hours in the past.

Although I've never come across the errors when turning a clock back, I'd
expect them to be in the opposite direction - a committed transaction
which thinks it was in the future, rather than an open transaction which
thinks it was opened ages ago.

Thanks,
Malcolm.


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