[Zope] ZODB replication on a per-object basis?

[Brad Clements]

On 11 May 2000, at 16:22, Petru Paler wrote:

> On Thu, May 11, 2000 at 09:03:22AM -0500, Brad Clements wrote:
> > However I need a way to "callback" into Zope to have it invalid its
> > internal cache of objects, forcing them to be re-read from the storage
> > manager.
> 
>     To put it simply, ZEO :)
> 
> -Petru

No, I don't think so.

From http://www.zope.org/Products/ZEO/ZEOFactSheet


> The pieces of ZEO discussed so far address scalability. For complete
> reliability, though, the data in the ZSS must be redundant. That is, the
> single point of failure cannot be simply shifted from the Zope process to
> the ZSS. The second level of the ZEO architecture eliminates the ZSS as the
> failure point by mirroring the object data between storage servers and
> allowing failover of one ZSS process to another. Scaling the Zope Storage
> Server will be the second phase of the ZEO work

Based on this, it appears that ZSS does not replicate at this time.

Also, the fact sheet says that Zope still caches objects in memory, but 
doesn't mention how a replicated ZSS can invalidate the cache of a 
running Zope process.

Invalidation is needed when another Zope process has changed an 
object.. That changed object needs to be pushed out to running Zope 
processes .. I imagine that some objects (like /index_html) are pretty 
much permanently cached in memory since they're hit so often.

Also, folder objects that are cached won't see new child objects from 
other zope processes until that folder is flushed and reloaded.

At least, this is what I'm assuming.. Someone correct me.

--

I'm looking for wide area replication .. like how you might implement a 
CPAN for Python based on Zope.



Brad Clements,                bkc@murkworks.com   (315)268-1000
http://www.murkworks.com                          (315)268-9812 Fax
netmeeting: ils://ils.murkworks.com               AOL-IM: BKClements