[Zope-dev] Cache code in Shared/DC/ZRDB/DA.py

[Tino Wildenhain]

Chris Withers schrieb:
> Hi Jim,
> 
> I'm wondering if you can still remember the rational behind the cache 
> code at around lines 355-387 of:
> 
> http://svn.zope.org/Zope/trunk/lib/python/Shared/DC/ZRDB/DA.py?rev=68158&view=auto 
> 
> 
> This code is pretty old (checked in 5th Dec 1997) but has started 
> causing a few people problems under high load:
> 
> http://mail.zope.org/pipermail/zope-db/2006-September/004684.html
> http://www.zope.org/Collectors/Zope/2212
> 
> In particular:
> 
> - in line 368, why is len(cache)>max_cache/2 used as a trigger to start 
> cache clearing? (the /2 in particular)
> 
> - does it matter that IOBTree.Bucket has gone away and that tcache is
>   now a simple dictionary? It certainly seems to make the keys.reverse()
>   on line 370 superfluous and the keys[-1]<t on line 371 less reliable.
> 
> More generally, do you or does anyone else have any attachment to this 
> code or would anyone mind if I ripped it out and replaced it with 
> something simpler, with more comments and unit tests?

I have a replacement started, which uses Cacheable mixin instead.
Advantage is, with RAM Cache Manager you can see the hits your method
cause and invalide the cache per object. I also introduced a execution
time treshold, so you can configure to only cache runtimes say above
1 sec, leaving more room for long running queries.

I think I should packe up what I have now (rough edges) so you
can have a look at it.

Tino.