[Zope] ZODB performance: reads to writes

[Jim Fulton]

Toby Dickenson wrote:
> 
> On Sat, 24 Jun 2000 12:43:05 -0400, "Evan Simpson" <evan@digicool.com>
> wrote:
> 
> >> Will an app as described above still suffer from problems with high
> >writes?
> 
> >There are two independent attacks on this problem underway:
> 
> >2. Implement the application-level conflict handling you read about, so that
> >Folders and Catalogs can decide that two writes don't conflict after all,
> >and merge them into a single update.
> 
> Yes, that will help
> 
> >1. Make Folders and Catalogs store meta-data about their contents in a data
> >structure consisting of small persistent objects, like B-Tree nodes.  This
> >reduces the scope of potential conflict (and the size of the update required
> >by a write) to the size of one of these nodes.
> 
> As I understand it, a BTreeFolder alone (ie without application-level
> conflict handling) will not help here.

Sure they will, because a BTree is the moral equivalent of
multiple subfolders. (This assumes that a problem in the current
BTree design is fixed, which it will be. ;)

> Folders have to ensure that all their contained elements have a
> different id. The hot-spot is the only way a Folder can achieve this.

But there is only a conflict if two transactions want to pick the 
same id.  Going to (fixed) BTrees doesn't prevent *all* conflicts, 
but it does prevent most conflicts, which will be good enough for many
applications.
 
Jim

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