[ZODB-Dev] ZEO 2

[Guido van Rossum]

> > I expect it's his ZEO cache.  Cache flips ever 40 seconds is not good.
> 
> I didnt think the cache size/characteristics had changed since ZEO
> 1? I had assumed that his ZEO 1 cache would have been flipping at
> the same rate, but without the log message he would never know.
> 
> Even if its not the underlying cause, it could be increasing the
> impact of some other problem.

Assuming Chris didn't have a larger ZEO cache when he was using ZEO
1.0, there's a change in the ZEO cache strategy that could negatively
affect its performance with sites that do a lot of writes (while
improving performance with sites that do many more reads than writes).
Here's the CVS log message:

    """
    Cache policy improvement:
    When load() finds a hit in the non-current file, copy it to the
    current file (except when this would cause a cache flip).

    It is hoped that this improves the cache performance.
    """

I'm not sure why this didn't make it into the ZEO-NEWS.txt file. :-(

--Guido van Rossum (home page: http://www.python.org/~guido/)