I'll like to take a stab at this one. I'm not sure though if I can create a branch or if I should create a fork. Which do You prefer?
-Jesper On ons, 2012-11-07 at 12:09 +0100, Jesper Damkjaer wrote: > Yes, I think it would. The problem is that the PID cannot be determined > until just before the call to objectExists(). And moving the > pidLock.getWriteLock() up here would essentially do the same as You > suggest. > > -Jesper > > On ons, 2012-11-07 at 10:57 +0000, Nicolas Hervé wrote: > > A lock on a unique object representing the PID to be inserted would be > > enough to prevent this, no ? > > ;ppvg usxd9ds=liiiiiiiiii > > On 06/11/2012 23:51, Jesper Damkjaer wrote: > > > It might be possible to simply just move the call to > > > pidLock.getWriteLock() up before the call to objectExists(). > > > Then the first thread will get the lock and the second thread will be > > > rejected. Even if the first thread have released the writelock, then it > > > will have registered the object and the second thread will be rejected > > > by objectExists(). > > > > > > This may of course give a false result if the first thread for some > > > reason fails to actually create the object. Then both threads are > > > rejected and no objects are created even though the second thread might > > > have succeeded (if it had won the race). > > > I believe we have another kind of locking mechanism which is a > > > stringLock. This lock doesnt reject the second thread - it just make it > > > wait until the first thread releases the lock. If this kind of lock is > > > used, then only one of the threads can enter the last part of > > > getIngestWriter (assuming the lock is before objectExists()) and if the > > > first thread succeeds the second thread will, upon release, get an > > > exception from objectExists(). If on the other hand, the first thread > > > fails to create an object then, when the lock is released, the second > > > thread can try to create the object. > > > > > > -Jesper > > > > > > > > > On tir, 2012-11-06 at 17:17 -0500, aj...@virginia.edu wrote: > > >> It's starting to sound like we need a pattern that is less constrictive > > >> of resources than the use of "synchronized", but still maintains some > > >> kind of guard against the kind of collision Jesper describes. A > > >> simpleminded thought: perhaps we could insert a lightweight check > > >> against the registry before registerObject() with a line of execution > > >> that backs out any changes if the check fails? Because it's an ingest, > > >> those changes shouldn't be hard to describe or undo. > > >> > > >> --- > > >> A. Soroka > > >> Software & Systems Engineering :: Online Library Environment > > >> the University of Virginia Library > > >> > > >> On Nov 6, 2012, at 4:22 PM, Jesper Damkjaer wrote: > > >> > > >>> I just had a quick look at the code. As far as I can see (and I may not > > >>> be right) one problem may be the following: > > >>> Assume both threads with same PID are inside the method getIngestWriter > > >>> and has passed the method-call objectExists(...). At this point neither > > >>> of the objects exists assuming none of the threads has yet reached > > >>> registerObject(...). > > >>> If one of the threads then get the writeLock, does what it needs to do > > >>> and releases the writeLock before the second thread reaches writeLock, > > >>> then the second thread will reach registerObject(...). As far as I can > > >>> tell, inside registerObject(...) an SQLException will be thrown since > > >>> the row already exists in the database, and the method > > >>> unregisterObject(...) will be called actually unregistering a legally > > >>> created object. > > >>> > > >>> Someone with more insight into the code should verify if the above is > > >>> correct. > > >>> > > >>> -Jesper > > >>> > > >>> > > >>> > > >>> On tir, 2012-11-06 at 21:44 +0100, Jesper Damkjaer wrote: > > >>>> Hi. > > >>>> > > >>>> I originally opened the https://jira.duraspace.org/browse/FCREPO-1024 > > >>>> I tried back then to create tests in order to convince myself that > > >>>> there > > >>>> would be no problems in removing the synchronization, but that proved > > >>>> rather difficult. > > >>>> As far as I remember there seemed to be some problems associated with > > >>>> removing the synchronization, especially if two documents with the same > > >>>> PID were ingested at the same time. > > >>>> I'm still interested in looking in to this, and will be happy to look > > >>>> at > > >>>> my old branch. > > >>>> > > >>>> -Jesper > > >>>> > > >>>> > > >>>> On tir, 2012-11-06 at 12:46 -0500, aj...@virginia.edu wrote: > > >>>>> There is a bit of history to this discussion: > > >>>>> > > >>>>> https://jira.duraspace.org/browse/FCREPO-1024 > > >>>>> > > >>>>> --- > > >>>>> A. Soroka > > >>>>> Software & Systems Engineering :: Online Library Environment > > >>>>> the University of Virginia Library > > >>>>> > > >>>>> On Nov 6, 2012, at 11:53 AM, Scott Prater wrote: > > >>>>> > > >>>>>> Nicolas, > > >>>>>> > > >>>>>> That's very encouraging... this problem has been on my radar for > > >>>>>> years. > > >>>>>> > > >>>>>> Not being very familiar with the details of the internals of > > >>>>>> DefaultDOManager, I can't comment concretely on the merits of your > > >>>>>> patch, but I would be especially interested in tests that provoke > > >>>>>> race conditions and concurrent writes, and makes sure Fedora handles > > >>>>>> those situations cleanly: even though PID generation is > > >>>>>> synchronized, would it still be possible for Fedora to attempt to > > >>>>>> write the same datastreams, provision identical values in the > > >>>>>> resource index, etc. in different threads once the object has been > > >>>>>> created and the PID assigned? As I dimly recall, I think the > > >>>>>> getIngestWriter method was synchronized because there were some > > >>>>>> problems in the early days with concurrent writes. That may be a > > >>>>>> non-issue now, though, if PID generation is synchronized (the Akubra > > >>>>>> storage layer is designed to handle writes more robustly). > > >>>>>> > > >>>>>> Another potential issue: if you're creating a hierarchical tree of > > >>>>>> objects in parallel, and the ingest of a parent object fails: you > > >>>>>> could be left with orphaned children. But that's something that > > >>>>>> should be checked and handled higher up the stack, with some > > >>>>>> transaction/rollback logic. > > >>>>>> > > >>>>>> -- Scott > > >>>>>> > > >>>>>> On 11/06/12, Nicolas Hervé wrote: > > >>>>>>> > > >>>>>>> > > >>>>>>> Hi, > > >>>>>>> > > >>>>>>> I think I've found the main problem with massive parallel ingestion. > > >>>>>>> > > >>>>>>> I'm working with the last github snapshot. > > >>>>>>> > > >>>>>>> In org.fcrepo.server.storage.DefaultDOManager, the getIngestWriter > > >>>>>>> method should not be synchronized as it seems there is only a > > >>>>>>> single instance of that class for the server. The internal objects > > >>>>>>> of this class seem to be correctly synchronized (pid generation) of > > >>>>>>> new objects are recreated on each call (inside Translator, a new > > >>>>>>> DODeserializer is created and the same happens inside the > > >>>>>>> Validator). > > >>>>>>> > > >>>>>>> I've tested with FOXML ingestion and now almost all the CPUs are > > >>>>>>> used. I've not been deeper to check that every inserted object is > > >>>>>>> not corrupted, but after a quick look, it seems OK. I guess the > > >>>>>>> same kind of patch could also apply on object deletion. > > >>>>>>> > > >>>>>>> If one of you that better understand that part could have a look, > > >>>>>>> it seems it would be a nice patch, not too hard to test, with great > > >>>>>>> performance improvements. > > >>>>>>> > > >>>>>>> Regards, > > >>>>>>> > > >>>>>>> Nicolas HERVE > > >>>>>>> > > >>>>>>> > > >>>>>>> On 28/09/2012 11:25, Nicolas Hervé wrote: > > >>>>>>> > > >>>>>>> > > >>>>>>>> Hi, > > >>>>>>>> > > >>>>>>>> indeed, it seems we are exactly in the same configuration > > >>>>>>>> (millions of DO with some metadata and external content) with > > >>>>>>>> almost the same hardware. I've not identified the bottleneck in > > >>>>>>>> the massive parallel ingestion process right now, but I highly > > >>>>>>>> suspect a synchronized portion of code somewhere in the chain. I > > >>>>>>>> hope Edwin could say more about this :-) > > >>>>>>>> > > >>>>>>>> For the querying of dc fields, index have to be created in the > > >>>>>>>> Mysql schema and SQL queries are far from being optimal. Currently > > >>>>>>>> I only patched for my own purposes (my datamodel / my queries) and > > >>>>>>>> I bypass some code portions in the following classes : > > >>>>>>>> > > >>>>>>>> org.fcrepo.server.search.FieldSearchSQLImpl > > >>>>>>>> org.fcrepo.server.search.FieldSearchResultSQLImpl > > >>>>>>>> > > >>>>>>>> I'm really new to Fedora Commons but, from what I understand, > > >>>>>>>> these SQL part is quite old. Changing them for optimizations > > >>>>>>>> purposes could imply behaviour changes for other people. That's > > >>>>>>>> why I don't think simple patches could do the job. It would need a > > >>>>>>>> complete refactoring. That could only be done with a global point > > >>>>>>>> of view on the different way this classes are used in the > > >>>>>>>> different contexts where Fedora instances are running. > > >>>>>>>> > > >>>>>>>> Feel free to contact me to discuss this more precisely. > > >>>>>>>> > > >>>>>>>> Regards, > > >>>>>>>> > > >>>>>>>> Nicolas HERVE > > >>>>>>>> +33 1 49 83 21 66 (GMT + 2) > > >>>>>>>> > > >>>>>>>> On 27/09/2012 18:23, Jason V wrote: > > >>>>>>>> > > >>>>>>>> > > >>>>>>>>> Hi Nicolas, > > >>>>>>>>> > > >>>>>>>>> My name is Jason Varghese and I'm a senior developer at the New > > >>>>>>>>> York Public Library. I think you are doing work similar to what I > > >>>>>>>>> am presently doing based on reading some of your posts. > > >>>>>>>>> > > >>>>>>>>> We have a relatively large scale Fedora implementation here. > > >>>>>>>>> We've had all the hardware in place for some time and are in the > > >>>>>>>>> process of migrating from a large homegrown repository to a > > >>>>>>>>> Fedora based platform. We have a single Fedora ingest machine and > > >>>>>>>>> 3 Fedora readers. The ingest machine alone is 4 x 6 core > > >>>>>>>>> processors w/ 128GB RAM. I'm in the process of generating about 1 > > >>>>>>>>> million+ digital objects and attaching to each DO all the > > >>>>>>>>> metadata (as managed content datastreams) and all the digital > > >>>>>>>>> assets (as external content datastreams). The digital assets > > >>>>>>>>> currently are about 183 TB of content (this is replicated at two > > >>>>>>>>> sites). I have a multithreaded java client I wrote to accomplish > > >>>>>>>>> the task for the Fedora ingest/DO generation and I use the > > >>>>>>>>> Mediashelf REST API client for connectivity to Fedora. I was able > > >>>>>>>>> to successfully ingest 10's of thousands of digital objects, but > > >>>>>>>>> really need ensure this process performs optimally and scales for > > >>>>>>>>> millions of objects. What bottlenecks were you able to identify > > >>>>>>>>> when running your multithreaded ingest process? Look forward to > > >>>>>>>>> learning/sharing experiences from this process with you and the > > >>>>>>>>> community and possibly collaborating. Thanks > > >>>>>>>>> > > >>>>>>>>> Jason Varghese > > >>>>>>>>> NYPL > > >>>>>>>>> > > >>>>>>>>> > > >>>>>>>> > > >>>>>>>> > > >>>>>>>> > > >>>>>>>> ------------------------------------------------------------------------------ > > >>>>>>>> Got visibility? Most devs has no idea what their production app > > >>>>>>>> looks like. Find out how fast your code is with AppDynamics Lite. > > >>>>>>>> http://ad.doubleclick.net/clk;262219671;13503038;y? > > >>>>>>>> http://info.appdynamics.com/FreeJavaPerformanceDownload.html > > >>>>>>>> > > >>>>>>>> > > >>>>>>>> > > >>>>>>>> _______________________________________________ > > >>>>>>>> Fedora-commons-users mailing list > > >>>>>>>> fedora-commons-us...@lists.sourceforge.net > > >>>>>>>> <fedora-commons-us...@lists.sourceforge.net> > > >>>>>>>> https://lists.sourceforge.net/lists/listinfo/fedora-commons-users > > >>>>>>>> > > >>>>>> -- > > >>>>>> -- > > >>>>>> Scott Prater > > >>>>>> Library, Instructional, and Research Applications (LIRA) > > >>>>>> Division of Information Technology (DoIT) > > >>>>>> University of Wisconsin - Madison > > >>>>>> pra...@wisc.edu > > >>>>>> > > >>>>>> ------------------------------------------------------------------------------ > > >>>>>> LogMeIn Central: Instant, anywhere, Remote PC access and management. > > >>>>>> Stay in control, update software, and manage PCs from one command > > >>>>>> center > > >>>>>> Diagnose problems and improve visibility into emerging IT issues > > >>>>>> Automate, monitor and manage. 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Do more in less time with Central > > >>>>> http://p.sf.net/sfu/logmein12331_d2d > > >>>>> _______________________________________________ > > >>>>> Fedora-commons-developers mailing list > > >>>>> Fedora-commons-developers@lists.sourceforge.net > > >>>>> https://lists.sourceforge.net/lists/listinfo/fedora-commons-developers > > >>>>> > > >>>>> > > >>>>> > > >>>> > > >>>> > > >>>> > > >>>> ------------------------------------------------------------------------------ > > >>>> LogMeIn Central: Instant, anywhere, Remote PC access and management. > > >>>> Stay in control, update software, and manage PCs from one command > > >>>> center > > >>>> Diagnose problems and improve visibility into emerging IT issues > > >>>> Automate, monitor and manage. Do more in less time with Central > > >>>> http://p.sf.net/sfu/logmein12331_d2d > > >>>> _______________________________________________ > > >>>> Fedora-commons-developers mailing list > > >>>> Fedora-commons-developers@lists.sourceforge.net > > >>>> https://lists.sourceforge.net/lists/listinfo/fedora-commons-developers > > >>> > > >>> > > >>> > > >>> ------------------------------------------------------------------------------ > > >>> LogMeIn Central: Instant, anywhere, Remote PC access and management. > > >>> Stay in control, update software, and manage PCs from one command center > > >>> Diagnose problems and improve visibility into emerging IT issues > > >>> Automate, monitor and manage. Do more in less time with Central > > >>> http://p.sf.net/sfu/logmein12331_d2d > > >>> _______________________________________________ > > >>> Fedora-commons-developers mailing list > > >>> Fedora-commons-developers@lists.sourceforge.net > > >>> https://lists.sourceforge.net/lists/listinfo/fedora-commons-developers > > >> > > >> ------------------------------------------------------------------------------ > > >> LogMeIn Central: Instant, anywhere, Remote PC access and management. > > >> Stay in control, update software, and manage PCs from one command center > > >> Diagnose problems and improve visibility into emerging IT issues > > >> Automate, monitor and manage. Do more in less time with Central > > >> http://p.sf.net/sfu/logmein12331_d2d > > >> _______________________________________________ > > >> Fedora-commons-developers mailing list > > >> Fedora-commons-developers@lists.sourceforge.net > > >> https://lists.sourceforge.net/lists/listinfo/fedora-commons-developers > > >> > > >> > > >> > > > > > > > > > > > > ------------------------------------------------------------------------------ > > > LogMeIn Central: Instant, anywhere, Remote PC access and management. > > > Stay in control, update software, and manage PCs from one command center > > > Diagnose problems and improve visibility into emerging IT issues > > > Automate, monitor and manage. Do more in less time with Central > > > http://p.sf.net/sfu/logmein12331_d2d > > > _______________________________________________ > > > Fedora-commons-developers mailing list > > > Fedora-commons-developers@lists.sourceforge.net > > > https://lists.sourceforge.net/lists/listinfo/fedora-commons-developers > > > > ------------------------------------------------------------------------------ > > LogMeIn Central: Instant, anywhere, Remote PC access and management. > > Stay in control, update software, and manage PCs from one command center > > Diagnose problems and improve visibility into emerging IT issues > > Automate, monitor and manage. 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