[Zope-dev] ZopePublication Competing writes/reads

[Laurence Rowe]

Hermann Himmelbauer wrote:
> Hi,
> Just by chance, I pressed the reload button of my browser for quite some time, 
> so that my Zope3-based site was reloaded over and over. I was surprised to 
> find the following in the logs:
> 
> 2008-10-20T18:45:15 WARNING ZopePublication Competing writes/reads 
> at /BSPSite/act/s/info: database conflict error (oid 0x0733, class 
> zope.session.session.SessionData)
> 
> Can someone explain me why this happens, if this is something dangerous or if 
> I can forget about it?
> 
> I tested the site with Apache Bench (ab2), with many concurrent requests and 
> could not reproduce the problem.
> 
> So my wild guess is the following: 
> I use session.PersistentSessionDataContainer for my session, so every request 
> will probably read/write to some Zope3 container/btree. And then, for some 
> reasons these reads/writes compete, which leads to the above warning. If I 
> use AB2, there's no cookie, thus no session, hence the problem does not 
> arise.
> 
> On the other hand, the zope root site (the Rotterdam ZMI) seems not to have 
> this problem, as it seems, I can't trigger this warning message with fast 
> reloads.

Presumably that site does not use sessioning so does not suffer from the 
same problem.

Laurence