[Zope-dev] ERROR(200) ZODB Couldn't load state for... Memory problem?

[Chris McDonough]

On Thu, 2004-07-22 at 18:51, Russ Ferriday wrote:
> Thanks, Chris.
> We're fronting two Zopes with Pound for load balancing. I can't
> seethere would be any connection with this error. But I mention it
> incase there's a pattern.

Well, I am too in this particular case, but I doubt the frontend matters
too much here.

> Also, the database came from 2.7.0 and an earlier python.

FTR that's also the case for me as well, but again I don't think that
matters here.

>  This lookslike resource starvation to me. The servers run for an hour
> or twothis problems shows up, becoming worse for a while, then we need
> arestart.

I think the problem is related to ZEO client storage "cache flips".  I
found an error in the log near the time of the "None has no attribute
seek" symptom indicating that the Zope process tried to "flip" a ZEO
cache file (by creating a new file) but UNIX file system permissions
apparently prevented it.  But then I turned off persistent ZEO client
cachefile storage (but omitting the "zeo-client-name" parameter from
zope.conf), believing this would be a workaround, but it hasn't been.  I
gave up at that point and that's where I am now.

> I'm try to debug it tomorrow. What would you look for? Any tips
> forresource monitoring?

I think it's resource-related only tangentially; it's a genuine bug that
only happens intermittently.  My theory is that it will happen as often
as a Zope client's ZEO client storage needs to flip its cache file.  
The cache file is only flipped when it exceeds a certain size and it
only exceeds a certain size after a certain pattern of usage causes it
to do so (lots of loads from the database of new items, typically).

It would be nice if you could confirm this.  Reading the Zope event log
file of the client that generated the error would be a good start.

- C