On Thu, Apr 12, 2012 at 4:35 PM, Emmanuel Lécharny <[email protected]>wrote:
> Forgot to reply to this mail, which raises interesting points. > > More inside. > > Le 4/11/12 10:38 PM, Alex Karasulu a écrit : > >> On Wed, Apr 11, 2012 at 4:04 PM, Emmanuel Lécharny<[email protected]>** >> wrote: >> >> I think we should add some mechanism in the server to check that >>> automatically, to avoid doing it by hand (there are hundreds of tests to >>> check...). One solution would be to keep a track of every cursor >>> construction in a HashMap, and to remove them when the cursor is closed. >>> The remaining cursors are likely not closed. >>> >> >> It would be nice to have a Cursor monitor that every opened Cursor >> registers with but this needs to happen automatically. Then when out of >> the >> creation scope the Cursor is expected to be closed and if not this is >> handled automatically. However does creation scope work well since >> sometimes we create Cursors and pass them up? >> > We do have a monitor, which is currently used to check that the cursor is > not closed when we try to use it. We certainly can use this monitor for > more than just checking such thing. > > Now, the pb is that the scope is not as easy to determinate than for a > variable in Java. For instance, if we consider persistent searches, or > paged searches, or even an abandonned search request, the scope is pretty > wide... > > Though we can have a set of rules that help us to close the cursor > automatically : > - if we get an exception during a SearchRequest, then the cursors must be > closed immediately. As soon as we store the cursors into the SearchContext, > this is pretty easy to do > - an AbandonRequest will close the cursor automatically too (getting the > cursor from the abandonned request) > - when we process the SearchResultDone, we can also close the cursor for > the current search request (this work for PagedSearch too) > - for pagedSearch, if the user reset the search by sending 0 as the > expected number of entries to return, then the cursor will be freed > - for persistent searches, as it will be closed by an unbind or an abandon > request, we are fine > - when a client unbinds, then all the pending cursors will be closed. > > All in all, we have everything needed to close the cursors automatically, > assuming we keep all the cursors into the session. > > These are really great suggestions and make the ideas I tried to express really tangible. Thanks for it Emmanuel. One technical point, we need to make Cursor close() operations idempotent if they are not already - meaning if we close a second time this should not cause an exception or change the outcome. > On the client side, this is another issue... As cursors are created by the > client code, we have no easy way to determinate when we should close the > cursors, except when the connection is closed or an abandon request/unbind > request is sent. Of course, when the server returns a searchResultDone we > could also close the cursor. Remains the situations where the client has > fetched some entries (but not all), and haven't unbind nor abandonned the > search. > > I think the aspect for automatic closing of cursors is left to be managed inside the server even though the API overlaps here. > In any case, this is less critical as we don't have to deal with the txn > layer. The client will just blow away with some nasty OOM sooner or > later... but this is not worse than what we get with NamingEnumeration in > JNDI, nah ? > > Yup +1 > Have I covered all the server options ? Or did I miss something ? > > >> This sounds like something that can be handled nicely using an aspect >> oriented solution. Now these things are heavy if you use AspectJ or >> something like that but other simpler solutions exist to bytecode splice >> compiled code to automatically handle these things. Maybe our past >> experiences with Aspects might make us reconsider. >> > A bit overkilling, IMO? > > I'm feeling the same but thought it should be just put out there. However we can achieve the same results perhaps with code or using a lighter mechanism with Proxy's via CGlib or something similar. These are just raw thought dumps so it's not a we SHOULD recommendation. Something to think about. -- Best Regards, -- Alex
