[Zope-dev] RAMCacheManager and object size

[Shane Hathaway]

Florent Guillaume wrote:
> The RAMCacheManager does a costly pseudo-pickling of the objects it 
> stores to compute their size, but that information is only used in  the
> statistics screen.

The motivation was actually more subtle: I wanted to prevent
applications from caching things that weren't self-contained.  As I saw
it, I would have otherwise spent countless hours debugging cache
problems, and the caching framework would have ultimately been rejected
as too fragile--similar to the fate of the Refresh product.

Catalog results in particular are an obvious thing to cache, but they
aren't safe for caching because they link back to the catalog.  You'd
have major thread problems and probably inconsistent results.  The
pickle machinery throws an exception when it hits many kinds of objects
that aren't self-contained, so it made a good match.  The only waste is
the time spent building a string.  It was only lucky that the string
could also be used for estimating memory consumption.

I think RAMCacheManager should, by default, continue to make a
reasonable attempt to ensure objects are safe for caching, but it might
be good to also have an advanced option that disables the filter.

> 2. or, how about using the size to have a cache threshold based on  the
> size. That would help manage memory consumption better. Has  anybody
> done something like that?

I don't think that has been attempted, but I agree it would be interesting.

Shane