Marcin, will you be including examples with OSCache?
Thanks, looking forward to read the cache docs! Cheers, Borut 2008/3/5 Marcin Skladaniec <[EMAIL PROTECTED]>: > Thank you very much for the reply, I need to read through one more time > and I'll try to make use of it as well as write some documentation down for > the website. > > Marcin > > > On 05/03/2008, at 9:20 PM, Andrus Adamchik wrote: > > > > On Mar 4, 2008, at 1:26 AM, Marcin Skladaniec wrote: > > > > Hi > > > > > > The documentation on caching ( > > > http://cayenne.apache.org/doc/caching-and-fresh-data.html and > > > http://cayenne.apache.org/doc/object-caching.html) isn't very > > > comprehensive, > > > > > > > Agreed. There are lots of new features related to caching in 3.0, and we > > do not communicate them well to the users as of yet. > > > > it does not answer questions like: > > > > > > - what is actually stored in cache pks? datarows ? objectIds ? > > > > > > > There are two types of cache: object cache [1] and query cache. > > > > * Object cache (stored at ObjectContext): Map<ObjectId, Persistent> (it > > may not be declared as such, but this is what it is). > > * Object cache (stored at DataDomain... so really a snapshot cache): > > Map<ObjectId, DataRow> > > * Query cache (stored at ObjectContext, aka LOCAL_CACHE): Map<String, > > List<Persistent|DataRow> > > * Query cache (stored at DataDomain, aka SHARED_CACHE): Map<String, > > List<DataRow> > > > > > > - does caching change when paging is on ? > > > > > > > Yes, there are some caveats, and a few things were tweaked recently. > > LOCAL_CACHE works (both ROP and two tier). There is no SHARED_CACHE support > > (and I want to make this more formal - throw an IllegalStateException if > > pagination and SHARED_CACHE are used together). One reason why I want to do > > that is that it appeared under ROP as if SHARED_CACHE worked, when it fact > > things worked differently, as a side effect of the special handling of > > paginated lists on the ROP server (see below). > > > > > > - does caching require special measures when used with ROP ? (meaning > > > the propagation of changes between contexts) > > > > > > > Not really, maybe an understanding of how it is implemented. Paginated > > list is always cached in the *server* local cache, regardless of the query > > cache settings. I.e. "LOCAL_CACHE + paginated list + ROP" means caching on > > both server and client; "NO_CACHE + paginated list + ROP" still means > > caching on the server. This is done in order to avoid transferring > > unresolved ID's to the client. > > > > > > - how to properly use SelectQuery.setCacheGroups()? > > > > > > > Cache groups are ignored unless you use advanced implementations of > > QueryCache on the server (e.g. OSCache). RefreshQuery can also target cache > > groups (see below). "cache group" is a mechanism to allow backend code to > > perform smart cache invalidation without knowing anything about the nature > > of the queries. E.g. you can have two groups "objects_that_change_often" and > > "objects_that_rarely_change", corresponding to 2 OSCache invalidation rules, > > "once per minute" vs. "once per day"... Now when you add new queries, you do > > not need to change configuration, if they fall into one of the existing > > "groups"... > > > > So the trick with cache groups is to find common data invalidation > > patterns in your app. Each repeating pattern becomes a group. This is a > > logical task, with very little code involved. > > > > what happens when a query has more than one cache group specified? > > > > > > > Invalidation rules for all groups are combined. I rarely used that in > > practice, but still think this allows some extra flexibility, e.g. if the > > same query falls in a broad category and also in a very specific one. E.g. > > "objects_that_rarely_change" and "objects_that_change_when_event_X_occurs". > > > > - how long the cache entries sit in the memory, is there a way to > > > invalidate all cache from time to time ? > > > > > > > Query cache (both shared and local): default mechanism is LRU and no > > expiration. OSCache allows to configure size and advanced expiration rules > > per cache group. > > > > Snapshot cache: LRU. Size configurable in the Modeler. > > > > Object cache (server): Unlimited size map with weak references. > > > > > > - how to invalidate cache using RefreshQuery, the > > > http://cayenne.apache.org/doc/refreshquery.html is just a list of > > > suggestions on how it might work in the future. > > > > > > > Yeah, this is not documented properly. I need to poke around a bit more > > to provide accurate information on RefreshQuery behavior. It was an early > > idea of cache handling, but I stopped using it in my own apps, as OSCache > > works beautifully, supports clustering, etc., etc. And rather importantly - > > it removes cache management logic from the code (i.e. explicit invalidation > > vs. configuration-based one). > > > > Me and Ari are willing to document the caching feature, but we would > > > need some help. > > > > > > > Awesome! I'd imagine the trick here is to separate everything discussed > > here into "internal-design-not-relevant-to-the-user" part and > > "cache-user-guide" part to avoid confusing people and exposing too many > > implementation details that will likely change over time. > > > > Andrus > > > > > > [1] http://cayenne.apache.org/doc/object-caching.html > > > > >
