[Zope] Cache settings?

[Michel Pelletier]

John Goerzen wrote:
> 
> Hi,
> 
> In the Control Panel, Database, Cache area, what does Target Size
> refer to?  Number of pages?  Kilobytes?  What does it mean by
> "target"?  What exactly is being cached?  Output from methods?  The
> method content themselves?  What is the difference between this and
> ZCache?

In this context 'cache' is the in-memory cache of Persistent objects
(most objects in Zope are persistent, for example, just about everything
you can add or manage in Zope is persisent).

Obviously, it's not very good performance to read and write all objects
to and from the database everytime you use them.  Therefore, there is a
cache to speed this up.

The 'target' is the number of objects in the cache.  Note that this is
not a very hard limit, ie, if you set it to 10, it will let you load 10
tiny objects or 10 huge ones.  Or 10 of mixed size.  Experimenting this
this value and watching how much memory Zope consumes is a good exercise
in performance tuning.  Note that there is NO magic value here, you have
to play with it.  Keep in mind that the default is very conservative,
you can definatly start playing with it in the up direction (unless your
running on a 386 with 16MB of RAM...).

-Michel