Hi guys, I think updateHeartBeat() method was misused in the future listener and this must be fixed.
Actually, GridWorker.heartbeatTs Javadoc says that field is updated by the worker itself. It is consistent with WorkProgressDispatcher.updateHearbeat() javadoc, which said "Notifying dispatcher that work is in progress and thread didn't freeze." GridWorker.heartbeatTs field is marked volatile just to provide consistent visibility guarantee to a watcher. So, CheckpointPagesWriter violates this contract, when runs in another thread(s). But it works fine just because the main (Checkpointer) thread waits for all the Writers to finish their work before it can fall into the blocking section, therefore there is no race possible. As for the broken case, there are 2 possible solutions, 1. Main thread must wait for all children's tasks to finish before going into the blocking section. 2. Or make updateHeartbeat consistent with the blockingSectionBegin/End. Seems, there is no need to mark the method as synchronized, but use call AtomicLongFieldUpdater.getAndUpdate(this, v -> v == Long.MAX_VALUE ? v : U.currentTimeMillis()). I'd suggest * Remove the "thread" mentioning from WorkProgressDispatcher interface to avoid confusion with the current usage and make WorkProgressDispatcher more general. * Avoid unsafe heartbeatUpdater leak to the outside via wrapping CheckpointContextImpl.heartbeatUpdater instance to perform consistent heartbeat update from p.2 above. Does it make sense? On Wed, Jul 21, 2021 at 11:12 AM Alex Plehanov <plehanov.a...@gmail.com> wrote: > Ilya, > > Race only affects the future listener (which only updates heartbeat), but > not checkpoint listeners, so no other bugs possible caused by this race > except wrong heartbeat update. > > As I've written before, I think it's not a good idea to wait for other > threads by the critical thread in the blocking section. If these threads > are not monitored we can never detect lack of progress and never trigger > the failure handler. Perhaps a good solution will be to register async > threads as critical threads (additionally to waiting for these threads in > the blocing section) and update their own heartbeat. But the current fix is > required too, to avoid such problems for other critical threads in the > future. > > ср, 21 июл. 2021 г. в 06:29, Ilya Kazakov <kazakov.i...@gmail.com>: > > > 1. > > I mean calling listeners in CheckpointWorkflow.markCheckpointBegin(): > > > > This > > ------------------------------------------ > > for (CheckpointListener lsnr : dbLsnrs) > > lsnr.beforeCheckpointBegin(ctx0); > > > > ctx0.awaitPendingTasksFinished(); > > ------------------------------------------ > > > > And this: > > > > ------------------------------------------ > > // Listeners must be invoked before we write checkpoint record to WAL. > > for (CheckpointListener lsnr : dbLsnrs) > > lsnr.onMarkCheckpointBegin(ctx0); > > > > ctx0.awaitPendingTasksFinished(); > > ------------------------------------------ > > > > Inside lsnr.beforeCheckpointBegin(ctx0) and > > lsnr.onMarkCheckpointBegin(ctx0) we call CheckpointContextImpl.executor() > > which submit heartbeat update tasks in threadpool. But due to a bug in > > registration, ctx0.awaitPendingTasksFinished() do not work correctly. > > Checpoint thread does not wait for all tasks to complete and moves on. > > > > This could lead to other bugs because as written in the comment "// > > Listeners must be invoked before we write checkpoint record to WAL." > > > > 2. > > About the fix. > > Yes, the fix resolves the issue, but does not resolve the root cause - a > > race between checkpoint thread and threads run in asyncRunner. Also, as I > > understand, there should be no attempts to update heartbeat inside > > blockingSection, but the fix does not exclude such attempts but blocks > them. > > > > 3. > > But my main point is that it looks strange to update the heartbeat of > > thread A from thread B. It's like doing artificial respiration and chest > > compressions. Thread A is waiting on async tasks completion, but these > > tasks are updating progress of thread A. I suppose that blockingSection > was > > designed for such situations when the thread is waiting for something and > > does not perform any progress. > > > > вт, 20 июл. 2021 г. в 21:43, Ivan Daschinsky <ivanda...@gmail.com>: > > > >> +1 For current fix. Code is clean and understandable. I suppose that the > >> current fix is a correct variant to update heartbeatTs. > >> > >> вт, 20 июл. 2021 г. в 16:13, Alex Plehanov <plehanov.a...@gmail.com>: > >> > >> > Hello, Ilya > >> > > >> > > But anyway, I propose to remove the update of the heartbeat from > other > >> > threads altogether and wrap the call to listeners in a > blockingSection. > >> > I don't quite understand your proposal. Which call to listeners do you > >> > mean? If we wrap the listener into the blocking section the result > will > >> be > >> > the same. > >> > Alternatively, I think we can wrap awaitPendingTasksFinished into the > >> > blocking section, this will also solve the problem, but in this case > we > >> can > >> > never detect lack of progress by async executor threads and > checkpointer > >> > thread hangs due to this reason. > >> > What's wrong with the current fix? It solves the current problem and I > >> hope > >> > will protect us from problems like this in the future. > >> > > >> > вт, 20 июл. 2021 г. в 15:28, Ilya Kazakov <kazakov.i...@gmail.com>: > >> > > >> > > Hi Igniters, hi Alexey. > >> > > > >> > > I want to discuss this issue: > >> > > https://issues.apache.org/jira/browse/IGNITE-15099. I have caught > it > >> > too. > >> > > > >> > > I was able to determine where there is a race. > >> > > > >> > > The update of the heartbeat happens asynchronously into the listener > >> > code. > >> > > But we always wait in the checkpoint thread for all pending async > >> > > tasks. And this is reasonable. > >> > > > >> > > for (CheckpointListener lsnr : dbLsnrs) > >> > > lsnr.beforeCheckpointBegin(ctx0); > >> > > > >> > > ctx0.awaitPendingTasksFinished(); > >> > > > >> > > The race was because of inappropriate order of future registration. > In > >> > > CheckpointContextImpl.executor () (inside listeners execution) > >> > > > >> > > GridFutureAdapter<?> res = new GridFutureAdapter<>(); > >> > > res.listen(fut -> heartbeatUpdater.updateHeartbeat()); > >> > > asyncRunner.execute(U.wrapIgniteFuture(cmd, res)); > >> > > pendingTaskFuture.add(res); > >> > > > >> > > Here we create a task, submit a task to the executor, and only after > >> this > >> > > do we register the task. Thus we got a situation where checkpointer > >> > thread > >> > > was moving on after ctx0.awaitPendingTasksFinished(); and still, > >> > > the unregistered asyncRunner task was moving on in parallel. > >> > > > >> > > But anyway, I propose to remove the update of the heartbeat from > other > >> > > threads altogether and wrap the call to listeners in a > >> blockingSection. > >> > > > >> > > As I understand heartbeat was designed just to indicate > self-progress > >> by > >> > a > >> > > worker. If a worker can not indicate self-progress we should wrap > such > >> > code > >> > > into blockingSections. In case of listeners, worker can not indicate > >> > > self-progress, thus let's wrap it into blockingSection. > >> > > > >> > > Guys, what do you think about this? > >> > > > >> > > ------------- > >> > > Ilya Kazakov > >> > > > >> > > >> > >> > >> -- > >> Sincerely yours, Ivan Daschinskiy > >> > > > -- Best regards, Andrey V. Mashenkov
