> On Feb 22, 2017, at 6:55 PM, Musall, Maik <[email protected]> wrote:
>
> Hi Andrus,
>
> ok, setting PersistenceState.HOLLOW works. So easy :-)
Ah great. We all just learned a new Cayenne trick :)
IIRC this also whacks to-many relationships, and those require a query to get
restored, as we can't guess relationship composition (another reason why I
gave up on managing graph refreshing in memory).
> I have cases where I have spent considerable resources to fetch large object
> graphs into memory, and then I'm sending off a few threads doing
> middle-duration asynchronous processing on a few objects, have them update an
> computed attribute and come back. When I'm receiving the message that object
> x is finished updating, it wouldn't make sense to refresh the entire object
> graph, let alone repeat any expensive db roundtrips.
Fair enough.
> However, I do have cases where I want to refresh the entire graph of objects
> in one ObjectContext, but I still want to make use of the snapshots to save
> the fetches if they tend to be expensive. This is how I'm doing it now, is
> this correct?
>
> for( Object obj : context.getGraphManager().registeredNodes() ) {
> ((DataObject)obj).setPersistenceState( PersistenceState.HOLLOW
> );
> }
>
> The assumption below all this of course is that I can only have one thread
> writing in one ObjectContext, although I can read on one ObjectContexts with
> several threads at once (like when using .parallelStream() on collections).
This will work, but will not be atomic (your readers will be consuming data in
the middle of invalidation ), and potentially will cycle through too many
objects.
Here is another idea. Assuming context #1 is where the changes happen, context
#2 is where the reads occur. When you need a full refresh, create context #3,
then transfer only the "entry point" objects from #2 via "localObject" and then
switch the readers to #3 at some point and let the rest of the graph gradually
inflate from cache. Again, no idea if that's workable in your setting.
Logically readers should not care if they get a separate copy of the graph, as
long as it is read-only. No?
Andrus
