Aaron, thanks a lot!
> On 21 May 2020, at 17:30, Aaron Rosenzweig <aa...@chatnbike.com> wrote: > It looks like you are mixing a couple things. Well probably I miss something of importance here. > If you are going to use Kieran’s code (I believe it was him initially) you > should use it fully and have a healthy number of coordinators If “the Kieran’s code” is exploiting of ERXObjectStoreCoordinatorPool.maxCoordinators > 1, well, we actually do not want to do that. We do that in other applications, but not in this one. Part of the normal processing which we do is locking the (one and only one) shared OSC to make sure some of the actions are well-serialised — it's more important than the speed. For normal processing (of page actions through R/R loops and their working threads) this causes no problem, quite the contrary, it's precisely what we want. Contrariwise, those import tasks are special for they (a) run with very low priority, (b) should not be affected by the main OSC lock (nor affect it and its users) at all. Thus... > I say that because his code does round robin and there is a chance that two > threads get the same coordinator under heavy load so you better stock up on > them. Think of each coordinator as a single cursor to the DB. ... creating a new coordinator for each import thread as “its own cursor to the DB” (or more precisely, its own EOF stack pretty independent on all the others) is precisely what I want. Actually those import tasks could be ideally run from another application or at least instance; only it would be a bit at the inconvenient side :) Is that wrong? Why? > For some reason you are telling Kieran’s code to only have one coordinator. > Then, on top of that, you make your own coordinator each time. It’s like > crossing the beams in Ghostbusters. Go one way, or the other, don’t mix. Probably I misunderstood the Kieran's code mightily. I do not need a coordinator pool far as I can say, and but for the default one OSC (which is shared by all the normal processing threads and ECs), I do not want coordinators reused, ever. Normally, there's at most one import task at given time (and they happen to be rather infrequent); nevertheless, if due to some extremely rare conditions it so happens and more imports runs at once, I'd still prefer each of them to have its own EOF stack/DB access, independent on all the others. > There is something to be said about rolling your own and ensuring every > thread has their own coordinator and then you don’t even need to lock. Yup, far as I understand, in this case, when the thread has its own EC in its own OSC none of which is ever shared with other threads, I believe locking in superfluous (but at the same time, harmless). > You would also want a queuing mechanism so that you don’t create too many > coordinators. Aside of the memory consumption (which we keep track of and is not too bad), why? In theory I can see the DB might reject too many connections, but that would hardly happen. Even if it did, I presume the fetch would thrown, not block?!? > If you are are not going to do that and want the easy button, embrace > Kieran’s code fully by making a large pool and letting his code give you an > EC to work with. Correct me please if I am wrong, but far as I understand, this could lead to the import EC sharing the OSC with some of normal sessions/worker threads, and that's definitely something we do not want to. I can add extra code to make sure it does not happen and to make sure sessions get one OSC and threads get others, but what would then be the advantage of that compared with creating one OSC for each import thread? > Think about how many people you expect to be using a long running task > concurrently and at least double that number for your pool size. In which case, what's precisely the advantage of having a pool instead of creating a new OSC for each import thread (and releasing it when the import is done)? > Don’t forget to send him some Red Breast Whiskey. Aha! At least one thing which I do not need more detailed elucidation :) Thanks again, OC >> On May 21, 2020, at 7:13 AM, OCsite via Webobjects-dev >> <webobjects-dev@lists.apple.com <mailto:webobjects-dev@lists.apple.com>> >> wrote: >> bumped lately into another weird problem. We import some data into DB in >> background tasks. Up to yesterday, it worked normally; today six import >> tasks were launched, and each of them seemingly hang in its first DB >> operation. Restart did help; alas, the site admins did not try to ask JVM to >> detect deadlocks when they restarted the application. >> >> The background task looks like this: >> >> === >> class ImportCSVTask extends ERXLongResponseTask.DefaultImplementation { >> def performAction { >> _thread.priority=Thread.MIN_PRIORITY >> try { >> try { >> editingContext=ERXEC.newEditingContext(objectStore=new >> EOObjectStoreCoordinator()) >> editingContext.lock() >> lognow 1, "=== preparing CSV import in EC $editingContext >> ===" >> >> formPrototype=ERXEOGlobalIDUtilities.fetchObjectWithGlobalID(editingContext,formPrototypeGID) >> lognow 1, "=== local prototype $formPrototype ===" >> ... ... >> === >> >> Always the “preparing” log was the last thing those threads presented; none >> of them ever reported “local prototype”. There's no other related log in >> there. >> >> Meantime the application ran normally and the worker tasks communicated with >> the database all right (with an occasional report that some select took >> 70-odd ms from ERXAdaptorChannelDelegate, we have the threshold at 50). We >> run with ERXObjectStoreCoordinatorPool.maxCoordinators=1. >> >> Any idea what could have gone wrong and how to find the culprit and prevent >> the problem in future? I thought a new EC in a new OSC can't be blocked for >> long, but self-evidently, I was wrong, they seemed to lock indefinitely >> (application was restarted ten-odd hours after the first import hanged after >> its “preparing” report, still no “local prototype”). >> >> Thanks and all the best, >> OC >> >> _______________________________________________ >> Do not post admin requests to the list. 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