On Thu, 2008-03-06 at 10:10 -0500, Ian Eslick wrote: > I agree with Robert. The best way to start is to use lisp as a > query > language and essential do a search/match over the object graph. > > The rub comes when you start looking at performance. A linear scan > of
I neglected to mention that in my use of Elephant, when I was attempting to run a commercial website, I was using the Data Collection Management (DCM) stuff that you can find in the contrib/rread directory of the project. This system provides strategy-based directors. That is, there is a basic factory object for each collection of objects that implements basic Create, Read, Update, Delete operations. When you initialize a director, you specify a storage strategy: *) In-memory hash, (no persistence, for transient objects) *) Elephant (no caching) *) Cache backed by Elephant (read in memory, with writes immediately flushed to the store) *) Generational system, in which each generation can have its own storage strategy. Everything Ian wrote in the last email about scanning and locality of reference makes perfect sense, but is assuming that you don't have every object cached. That approach is therefore not very "Prevalence"-like in its performance, but is very "Prevalence"-like in its convenience. Using DCM, or any other caching where most of the object are cached, tends to you go the performance described in the IBM article on Prevalence that I referenced. However, DCM was written BEFORE Ian got the class indexing and persistence working. DCM is not nearly as pretty and clean as the persistent classes. You end up having to make storage decisions yourself. A perfect system might be persistent classes with really excellent control over the caching/write-updating policy. For any application, I a would recommend using Ian's persistent classes at the beginning project stages, and then when your performance tests reveal you have a problem, consider at that point whether to add indexes, move to explicitly keeping a class in memory, or some other solution. _______________________________________________ elephant-devel site list elephant-devel@common-lisp.net http://common-lisp.net/mailman/listinfo/elephant-devel
