Quick question for option 1.1 Stephan: Does this variant entail that we distinguish between native and direct memory off heap managed memory? If this is the case, then it won't be possible for users to run a streaming job using RocksDB and a batch DataSet job on the same session cluster unless they have configured the off heap managed memory to be twofold (e.g. 50% native, 50% direct memory).
Cheers, Till On Mon, Aug 19, 2019 at 4:21 PM JingsongLee <lzljs3620...@aliyun.com.invalid> wrote: > Hi stephan: > > About option 2: > > if additional threads not cleanly shut down before we can exit the task: > In the current case of memory reuse, it has freed up the memory it > uses. If this memory is used by other tasks and asynchronous threads > of exited task may still be writing, there will be concurrent security > problems, and even lead to errors in user computing results. > > So I think this is a serious and intolerable bug, No matter what the > option is, it should be avoided. > > About direct memory cleaned by GC: > I don't think it is a good idea, I've encountered so many situations > that it's too late for GC to cause DirectMemory OOM. Release and > allocate DirectMemory depend on the type of user job, which is > often beyond our control. > > Best, > Jingsong Lee > > > ------------------------------------------------------------------ > From:Stephan Ewen <se...@apache.org> > Send Time:2019年8月19日(星期一) 15:56 > To:dev <dev@flink.apache.org> > Subject:Re: [DISCUSS] FLIP-49: Unified Memory Configuration for > TaskExecutors > > My main concern with option 2 (manually release memory) is that segfaults > in the JVM send off all sorts of alarms on user ends. So we need to > guarantee that this never happens. > > The trickyness is in tasks that uses data structures / algorithms with > additional threads, like hash table spill/read and sorting threads. We need > to ensure that these cleanly shut down before we can exit the task. > I am not sure that we have that guaranteed already, that's why option 1.1 > seemed simpler to me. > > On Mon, Aug 19, 2019 at 3:42 PM Xintong Song <tonysong...@gmail.com> > wrote: > > > Thanks for the comments, Stephan. Summarized in this way really makes > > things easier to understand. > > > > I'm in favor of option 2, at least for the moment. I think it is not that > > difficult to keep it segfault safe for memory manager, as long as we > always > > de-allocate the memory segment when it is released from the memory > > consumers. Only if the memory consumer continue using the buffer of > memory > > segment after releasing it, in which case we do want the job to fail so > we > > detect the memory leak early. > > > > For option 1.2, I don't think this is a good idea. Not only because the > > assumption (regular GC is enough to clean direct buffers) may not always > be > > true, but also it makes harder for finding problems in cases of memory > > overuse. E.g., user configured some direct memory for the user libraries. > > If the library actually use more direct memory then configured, which > > cannot be cleaned by GC because they are still in use, may lead to > overuse > > of the total container memory. In that case, if it didn't touch the JVM > > default max direct memory limit, we cannot get a direct memory OOM and it > > will become super hard to understand which part of the configuration need > > to be updated. > > > > For option 1.1, it has the similar problem as 1.2, if the exceeded direct > > memory does not reach the max direct memory limit specified by the > > dedicated parameter. I think it is slightly better than 1.2, only because > > we can tune the parameter. > > > > Thank you~ > > > > Xintong Song > > > > > > > > On Mon, Aug 19, 2019 at 2:53 PM Stephan Ewen <se...@apache.org> wrote: > > > > > About the "-XX:MaxDirectMemorySize" discussion, maybe let me summarize > > it a > > > bit differently: > > > > > > We have the following two options: > > > > > > (1) We let MemorySegments be de-allocated by the GC. That makes it > > segfault > > > safe. But then we need a way to trigger GC in case de-allocation and > > > re-allocation of a bunch of segments happens quickly, which is often > the > > > case during batch scheduling or task restart. > > > - The "-XX:MaxDirectMemorySize" (option 1.1) is one way to do this > > > - Another way could be to have a dedicated bookkeeping in the > > > MemoryManager (option 1.2), so that this is a number independent of the > > > "-XX:MaxDirectMemorySize" parameter. > > > > > > (2) We manually allocate and de-allocate the memory for the > > MemorySegments > > > (option 2). That way we need not worry about triggering GC by some > > > threshold or bookkeeping, but it is harder to prevent segfaults. We > need > > to > > > be very careful about when we release the memory segments (only in the > > > cleanup phase of the main thread). > > > > > > If we go with option 1.1, we probably need to set > > > "-XX:MaxDirectMemorySize" to "off_heap_managed_memory + direct_memory" > > and > > > have "direct_memory" as a separate reserved memory pool. Because if we > > just > > > set "-XX:MaxDirectMemorySize" to "off_heap_managed_memory + > > jvm_overhead", > > > then there will be times when that entire memory is allocated by direct > > > buffers and we have nothing left for the JVM overhead. So we either > need > > a > > > way to compensate for that (again some safety margin cutoff value) or > we > > > will exceed container memory. > > > > > > If we go with option 1.2, we need to be aware that it takes elaborate > > logic > > > to push recycling of direct buffers without always triggering a full > GC. > > > > > > > > > My first guess is that the options will be easiest to do in the > following > > > order: > > > > > > - Option 1.1 with a dedicated direct_memory parameter, as discussed > > > above. We would need to find a way to set the direct_memory parameter > by > > > default. We could start with 64 MB and see how it goes in practice. One > > > danger I see is that setting this loo low can cause a bunch of > additional > > > GCs compared to before (we need to watch this carefully). > > > > > > - Option 2. It is actually quite simple to implement, we could try > how > > > segfault safe we are at the moment. > > > > > > - Option 1.2: We would not touch the "-XX:MaxDirectMemorySize" > > parameter > > > at all and assume that all the direct memory allocations that the JVM > and > > > Netty do are infrequent enough to be cleaned up fast enough through > > regular > > > GC. I am not sure if that is a valid assumption, though. > > > > > > Best, > > > Stephan > > > > > > > > > > > > On Fri, Aug 16, 2019 at 2:16 PM Xintong Song <tonysong...@gmail.com> > > > wrote: > > > > > > > Thanks for sharing your opinion Till. > > > > > > > > I'm also in favor of alternative 2. I was wondering whether we can > > avoid > > > > using Unsafe.allocate() for off-heap managed memory and network > memory > > > with > > > > alternative 3. But after giving it a second thought, I think even for > > > > alternative 3 using direct memory for off-heap managed memory could > > cause > > > > problems. > > > > > > > > Hi Yang, > > > > > > > > Regarding your concern, I think what proposed in this FLIP it to have > > > both > > > > off-heap managed memory and network memory allocated through > > > > Unsafe.allocate(), which means they are practically native memory and > > not > > > > limited by JVM max direct memory. The only parts of memory limited by > > JVM > > > > max direct memory are task off-heap memory and JVM overhead, which > are > > > > exactly alternative 2 suggests to set the JVM max direct memory to. > > > > > > > > Thank you~ > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > On Fri, Aug 16, 2019 at 1:48 PM Till Rohrmann <trohrm...@apache.org> > > > > wrote: > > > > > > > > > Thanks for the clarification Xintong. I understand the two > > alternatives > > > > > now. > > > > > > > > > > I would be in favour of option 2 because it makes things explicit. > If > > > we > > > > > don't limit the direct memory, I fear that we might end up in a > > similar > > > > > situation as we are currently in: The user might see that her > process > > > > gets > > > > > killed by the OS and does not know why this is the case. > > Consequently, > > > > she > > > > > tries to decrease the process memory size (similar to increasing > the > > > > cutoff > > > > > ratio) in order to accommodate for the extra direct memory. Even > > worse, > > > > she > > > > > tries to decrease memory budgets which are not fully used and hence > > > won't > > > > > change the overall memory consumption. > > > > > > > > > > Cheers, > > > > > Till > > > > > > > > > > On Fri, Aug 16, 2019 at 11:01 AM Xintong Song < > tonysong...@gmail.com > > > > > > > > wrote: > > > > > > > > > > > Let me explain this with a concrete example Till. > > > > > > > > > > > > Let's say we have the following scenario. > > > > > > > > > > > > Total Process Memory: 1GB > > > > > > JVM Direct Memory (Task Off-Heap Memory + JVM Overhead): 200MB > > > > > > Other Memory (JVM Heap Memory, JVM Metaspace, Off-Heap Managed > > Memory > > > > and > > > > > > Network Memory): 800MB > > > > > > > > > > > > > > > > > > For alternative 2, we set -XX:MaxDirectMemorySize to 200MB. > > > > > > For alternative 3, we set -XX:MaxDirectMemorySize to a very large > > > > value, > > > > > > let's say 1TB. > > > > > > > > > > > > If the actual direct memory usage of Task Off-Heap Memory and JVM > > > > > Overhead > > > > > > do not exceed 200MB, then alternative 2 and alternative 3 should > > have > > > > the > > > > > > same utility. Setting larger -XX:MaxDirectMemorySize will not > > reduce > > > > the > > > > > > sizes of the other memory pools. > > > > > > > > > > > > If the actual direct memory usage of Task Off-Heap Memory and JVM > > > > > > Overhead potentially exceed 200MB, then > > > > > > > > > > > > - Alternative 2 suffers from frequent OOM. To avoid that, the > > only > > > > > thing > > > > > > user can do is to modify the configuration and increase JVM > > Direct > > > > > > Memory > > > > > > (Task Off-Heap Memory + JVM Overhead). Let's say that user > > > increases > > > > > JVM > > > > > > Direct Memory to 250MB, this will reduce the total size of > other > > > > > memory > > > > > > pools to 750MB, given the total process memory remains 1GB. > > > > > > - For alternative 3, there is no chance of direct OOM. There > are > > > > > chances > > > > > > of exceeding the total process memory limit, but given that > the > > > > > process > > > > > > may > > > > > > not use up all the reserved native memory (Off-Heap Managed > > > Memory, > > > > > > Network > > > > > > Memory, JVM Metaspace), if the actual direct memory usage is > > > > slightly > > > > > > above > > > > > > yet very close to 200MB, user probably do not need to change > the > > > > > > configurations. > > > > > > > > > > > > Therefore, I think from the user's perspective, a feasible > > > > configuration > > > > > > for alternative 2 may lead to lower resource utilization compared > > to > > > > > > alternative 3. > > > > > > > > > > > > Thank you~ > > > > > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Aug 16, 2019 at 10:28 AM Till Rohrmann < > > trohrm...@apache.org > > > > > > > > > > wrote: > > > > > > > > > > > > > I guess you have to help me understand the difference between > > > > > > alternative 2 > > > > > > > and 3 wrt to memory under utilization Xintong. > > > > > > > > > > > > > > - Alternative 2: set XX:MaxDirectMemorySize to Task Off-Heap > > Memory > > > > and > > > > > > JVM > > > > > > > Overhead. Then there is the risk that this size is too low > > > resulting > > > > > in a > > > > > > > lot of garbage collection and potentially an OOM. > > > > > > > - Alternative 3: set XX:MaxDirectMemorySize to something larger > > > than > > > > > > > alternative 2. This would of course reduce the sizes of the > other > > > > > memory > > > > > > > types. > > > > > > > > > > > > > > How would alternative 2 now result in an under utilization of > > > memory > > > > > > > compared to alternative 3? If alternative 3 strictly sets a > > higher > > > > max > > > > > > > direct memory size and we use only little, then I would expect > > that > > > > > > > alternative 3 results in memory under utilization. > > > > > > > > > > > > > > Cheers, > > > > > > > Till > > > > > > > > > > > > > > On Tue, Aug 13, 2019 at 4:19 PM Yang Wang < > danrtsey...@gmail.com > > > > > > > > wrote: > > > > > > > > > > > > > > > Hi xintong,till > > > > > > > > > > > > > > > > > > > > > > > > > Native and Direct Memory > > > > > > > > > > > > > > > > My point is setting a very large max direct memory size when > we > > > do > > > > > not > > > > > > > > differentiate direct and native memory. If the direct > > > > > memory,including > > > > > > > user > > > > > > > > direct memory and framework direct memory,could be calculated > > > > > > > > correctly,then > > > > > > > > i am in favor of setting direct memory with fixed value. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Memory Calculation > > > > > > > > > > > > > > > > I agree with xintong. For Yarn and k8s,we need to check the > > > memory > > > > > > > > configurations in client to avoid submitting successfully and > > > > failing > > > > > > in > > > > > > > > the flink master. > > > > > > > > > > > > > > > > > > > > > > > > Best, > > > > > > > > > > > > > > > > Yang > > > > > > > > > > > > > > > > Xintong Song <tonysong...@gmail.com>于2019年8月13日 周二22:07写道： > > > > > > > > > > > > > > > > > Thanks for replying, Till. > > > > > > > > > > > > > > > > > > About MemorySegment, I think you are right that we should > not > > > > > include > > > > > > > > this > > > > > > > > > issue in the scope of this FLIP. This FLIP should > concentrate > > > on > > > > > how > > > > > > to > > > > > > > > > configure memory pools for TaskExecutors, with minimum > > > > involvement > > > > > on > > > > > > > how > > > > > > > > > memory consumers use it. > > > > > > > > > > > > > > > > > > About direct memory, I think alternative 3 may not having > the > > > > same > > > > > > over > > > > > > > > > reservation issue that alternative 2 does, but at the cost > of > > > > risk > > > > > of > > > > > > > > over > > > > > > > > > using memory at the container level, which is not good. My > > > point > > > > is > > > > > > > that > > > > > > > > > both "Task Off-Heap Memory" and "JVM Overhead" are not easy > > to > > > > > > config. > > > > > > > > For > > > > > > > > > alternative 2, users might configure them higher than what > > > > actually > > > > > > > > needed, > > > > > > > > > just to avoid getting a direct OOM. For alternative 3, > users > > do > > > > not > > > > > > get > > > > > > > > > direct OOM, so they may not config the two options > > aggressively > > > > > high. > > > > > > > But > > > > > > > > > the consequences are risks of overall container memory > usage > > > > > exceeds > > > > > > > the > > > > > > > > > budget. > > > > > > > > > > > > > > > > > > Thank you~ > > > > > > > > > > > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Tue, Aug 13, 2019 at 9:39 AM Till Rohrmann < > > > > > trohrm...@apache.org> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > Thanks for proposing this FLIP Xintong. > > > > > > > > > > > > > > > > > > > > All in all I think it already looks quite good. > Concerning > > > the > > > > > > first > > > > > > > > open > > > > > > > > > > question about allocating memory segments, I was > wondering > > > > > whether > > > > > > > this > > > > > > > > > is > > > > > > > > > > strictly necessary to do in the context of this FLIP or > > > whether > > > > > > this > > > > > > > > > could > > > > > > > > > > be done as a follow up? Without knowing all details, I > > would > > > be > > > > > > > > concerned > > > > > > > > > > that we would widen the scope of this FLIP too much > because > > > we > > > > > > would > > > > > > > > have > > > > > > > > > > to touch all the existing call sites of the MemoryManager > > > where > > > > > we > > > > > > > > > allocate > > > > > > > > > > memory segments (this should mainly be batch operators). > > The > > > > > > addition > > > > > > > > of > > > > > > > > > > the memory reservation call to the MemoryManager should > not > > > be > > > > > > > affected > > > > > > > > > by > > > > > > > > > > this and I would hope that this is the only point of > > > > interaction > > > > > a > > > > > > > > > > streaming job would have with the MemoryManager. > > > > > > > > > > > > > > > > > > > > Concerning the second open question about setting or not > > > > setting > > > > > a > > > > > > > max > > > > > > > > > > direct memory limit, I would also be interested why Yang > > Wang > > > > > > thinks > > > > > > > > > > leaving it open would be best. My concern about this > would > > be > > > > > that > > > > > > we > > > > > > > > > would > > > > > > > > > > be in a similar situation as we are now with the > > > > > > RocksDBStateBackend. > > > > > > > > If > > > > > > > > > > the different memory pools are not clearly separated and > > can > > > > > spill > > > > > > > over > > > > > > > > > to > > > > > > > > > > a different pool, then it is quite hard to understand > what > > > > > exactly > > > > > > > > > causes a > > > > > > > > > > process to get killed for using too much memory. This > could > > > > then > > > > > > > easily > > > > > > > > > > lead to a similar situation what we have with the > > > cutoff-ratio. > > > > > So > > > > > > > why > > > > > > > > > not > > > > > > > > > > setting a sane default value for max direct memory and > > giving > > > > the > > > > > > > user > > > > > > > > an > > > > > > > > > > option to increase it if he runs into an OOM. > > > > > > > > > > > > > > > > > > > > @Xintong, how would alternative 2 lead to lower memory > > > > > utilization > > > > > > > than > > > > > > > > > > alternative 3 where we set the direct memory to a higher > > > value? > > > > > > > > > > > > > > > > > > > > Cheers, > > > > > > > > > > Till > > > > > > > > > > > > > > > > > > > > On Fri, Aug 9, 2019 at 9:12 AM Xintong Song < > > > > > tonysong...@gmail.com > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > Thanks for the feedback, Yang. > > > > > > > > > > > > > > > > > > > > > > Regarding your comments: > > > > > > > > > > > > > > > > > > > > > > *Native and Direct Memory* > > > > > > > > > > > I think setting a very large max direct memory size > > > > definitely > > > > > > has > > > > > > > > some > > > > > > > > > > > good sides. E.g., we do not worry about direct OOM, and > > we > > > > > don't > > > > > > > even > > > > > > > > > > need > > > > > > > > > > > to allocate managed / network memory with > > > Unsafe.allocate() . > > > > > > > > > > > However, there are also some down sides of doing this. > > > > > > > > > > > > > > > > > > > > > > - One thing I can think of is that if a task > executor > > > > > > container > > > > > > > is > > > > > > > > > > > killed due to overusing memory, it could be hard for > > use > > > > to > > > > > > know > > > > > > > > > which > > > > > > > > > > > part > > > > > > > > > > > of the memory is overused. > > > > > > > > > > > - Another down side is that the JVM never trigger GC > > due > > > > to > > > > > > > > reaching > > > > > > > > > > max > > > > > > > > > > > direct memory limit, because the limit is too high > to > > be > > > > > > > reached. > > > > > > > > > That > > > > > > > > > > > means we kind of relay on heap memory to trigger GC > > and > > > > > > release > > > > > > > > > direct > > > > > > > > > > > memory. That could be a problem in cases where we > have > > > > more > > > > > > > direct > > > > > > > > > > > memory > > > > > > > > > > > usage but not enough heap activity to trigger the > GC. > > > > > > > > > > > > > > > > > > > > > > Maybe you can share your reasons for preferring > setting a > > > > very > > > > > > > large > > > > > > > > > > value, > > > > > > > > > > > if there are anything else I overlooked. > > > > > > > > > > > > > > > > > > > > > > *Memory Calculation* > > > > > > > > > > > If there is any conflict between multiple configuration > > > that > > > > > user > > > > > > > > > > > explicitly specified, I think we should throw an error. > > > > > > > > > > > I think doing checking on the client side is a good > idea, > > > so > > > > > that > > > > > > > on > > > > > > > > > > Yarn / > > > > > > > > > > > K8s we can discover the problem before submitting the > > Flink > > > > > > > cluster, > > > > > > > > > > which > > > > > > > > > > > is always a good thing. > > > > > > > > > > > But we can not only rely on the client side checking, > > > because > > > > > for > > > > > > > > > > > standalone cluster TaskManagers on different machines > may > > > > have > > > > > > > > > different > > > > > > > > > > > configurations and the client does see that. > > > > > > > > > > > What do you think? > > > > > > > > > > > > > > > > > > > > > > Thank you~ > > > > > > > > > > > > > > > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Aug 8, 2019 at 5:09 PM Yang Wang < > > > > > danrtsey...@gmail.com> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > Hi xintong, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for your detailed proposal. After all the > memory > > > > > > > > configuration > > > > > > > > > > are > > > > > > > > > > > > introduced, it will be more powerful to control the > > flink > > > > > > memory > > > > > > > > > > usage. I > > > > > > > > > > > > just have few questions about it. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - Native and Direct Memory > > > > > > > > > > > > > > > > > > > > > > > > We do not differentiate user direct memory and native > > > > memory. > > > > > > > They > > > > > > > > > are > > > > > > > > > > > all > > > > > > > > > > > > included in task off-heap memory. Right? So i don’t > > think > > > > we > > > > > > > could > > > > > > > > > not > > > > > > > > > > > set > > > > > > > > > > > > the -XX:MaxDirectMemorySize properly. I prefer > leaving > > > it a > > > > > > very > > > > > > > > > large > > > > > > > > > > > > value. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - Memory Calculation > > > > > > > > > > > > > > > > > > > > > > > > If the sum of and fine-grained memory(network memory, > > > > managed > > > > > > > > memory, > > > > > > > > > > > etc.) > > > > > > > > > > > > is larger than total process memory, how do we deal > > with > > > > this > > > > > > > > > > situation? > > > > > > > > > > > Do > > > > > > > > > > > > we need to check the memory configuration in client? > > > > > > > > > > > > > > > > > > > > > > > > Xintong Song <tonysong...@gmail.com> 于2019年8月7日周三 > > > > 下午10:14写道： > > > > > > > > > > > > > > > > > > > > > > > > > Hi everyone, > > > > > > > > > > > > > > > > > > > > > > > > > > We would like to start a discussion thread on > > "FLIP-49: > > > > > > Unified > > > > > > > > > > Memory > > > > > > > > > > > > > Configuration for TaskExecutors"[1], where we > > describe > > > > how > > > > > to > > > > > > > > > improve > > > > > > > > > > > > > TaskExecutor memory configurations. The FLIP > document > > > is > > > > > > mostly > > > > > > > > > based > > > > > > > > > > > on > > > > > > > > > > > > an > > > > > > > > > > > > > early design "Memory Management and Configuration > > > > > > Reloaded"[2] > > > > > > > by > > > > > > > > > > > > Stephan, > > > > > > > > > > > > > with updates from follow-up discussions both online > > and > > > > > > > offline. > > > > > > > > > > > > > > > > > > > > > > > > > > This FLIP addresses several shortcomings of current > > > > (Flink > > > > > > 1.9) > > > > > > > > > > > > > TaskExecutor memory configuration. > > > > > > > > > > > > > > > > > > > > > > > > > > - Different configuration for Streaming and > Batch. > > > > > > > > > > > > > - Complex and difficult configuration of RocksDB > > in > > > > > > > Streaming. > > > > > > > > > > > > > - Complicated, uncertain and hard to understand. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Key changes to solve the problems can be summarized > > as > > > > > > follows. > > > > > > > > > > > > > > > > > > > > > > > > > > - Extend memory manager to also account for > memory > > > > usage > > > > > > by > > > > > > > > > state > > > > > > > > > > > > > backends. > > > > > > > > > > > > > - Modify how TaskExecutor memory is partitioned > > > > > accounted > > > > > > > > > > individual > > > > > > > > > > > > > memory reservations and pools. > > > > > > > > > > > > > - Simplify memory configuration options and > > > > calculations > > > > > > > > logics. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Please find more details in the FLIP wiki document > > [1]. > > > > > > > > > > > > > > > > > > > > > > > > > > (Please note that the early design doc [2] is out > of > > > > sync, > > > > > > and > > > > > > > it > > > > > > > > > is > > > > > > > > > > > > > appreciated to have the discussion in this mailing > > list > > > > > > > thread.) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Looking forward to your feedbacks. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thank you~ > > > > > > > > > > > > > > > > > > > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > [1] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-49%3A+Unified+Memory+Configuration+for+TaskExecutors > > > > > > > > > > > > > > > > > > > > > > > > > > [2] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://docs.google.com/document/d/1o4KvyyXsQMGUastfPin3ZWeUXWsJgoL7piqp1fFYJvA/edit?usp=sharing > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Aug 16, 2019 at 2:16 PM Xintong Song <tonysong...@gmail.com> > > > wrote: > > > > > > > Thanks for sharing your opinion Till. > > > > > > > > I'm also in favor of alternative 2. I was wondering whether we can > > avoid > > > > using Unsafe.allocate() for off-heap managed memory and network > memory > > > with > > > > alternative 3. But after giving it a second thought, I think even for > > > > alternative 3 using direct memory for off-heap managed memory could > > cause > > > > problems. > > > > > > > > Hi Yang, > > > > > > > > Regarding your concern, I think what proposed in this FLIP it to have > > > both > > > > off-heap managed memory and network memory allocated through > > > > Unsafe.allocate(), which means they are practically native memory and > > not > > > > limited by JVM max direct memory. The only parts of memory limited by > > JVM > > > > max direct memory are task off-heap memory and JVM overhead, which > are > > > > exactly alternative 2 suggests to set the JVM max direct memory to. > > > > > > > > Thank you~ > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > On Fri, Aug 16, 2019 at 1:48 PM Till Rohrmann <trohrm...@apache.org> > > > > wrote: > > > > > > > > > Thanks for the clarification Xintong. I understand the two > > alternatives > > > > > now. > > > > > > > > > > I would be in favour of option 2 because it makes things explicit. > If > > > we > > > > > don't limit the direct memory, I fear that we might end up in a > > similar > > > > > situation as we are currently in: The user might see that her > process > > > > gets > > > > > killed by the OS and does not know why this is the case. > > Consequently, > > > > she > > > > > tries to decrease the process memory size (similar to increasing > the > > > > cutoff > > > > > ratio) in order to accommodate for the extra direct memory. Even > > worse, > > > > she > > > > > tries to decrease memory budgets which are not fully used and hence > > > won't > > > > > change the overall memory consumption. > > > > > > > > > > Cheers, > > > > > Till > > > > > > > > > > On Fri, Aug 16, 2019 at 11:01 AM Xintong Song < > tonysong...@gmail.com > > > > > > > > wrote: > > > > > > > > > > > Let me explain this with a concrete example Till. > > > > > > > > > > > > Let's say we have the following scenario. > > > > > > > > > > > > Total Process Memory: 1GB > > > > > > JVM Direct Memory (Task Off-Heap Memory + JVM Overhead): 200MB > > > > > > Other Memory (JVM Heap Memory, JVM Metaspace, Off-Heap Managed > > Memory > > > > and > > > > > > Network Memory): 800MB > > > > > > > > > > > > > > > > > > For alternative 2, we set -XX:MaxDirectMemorySize to 200MB. > > > > > > For alternative 3, we set -XX:MaxDirectMemorySize to a very large > > > > value, > > > > > > let's say 1TB. > > > > > > > > > > > > If the actual direct memory usage of Task Off-Heap Memory and JVM > > > > > Overhead > > > > > > do not exceed 200MB, then alternative 2 and alternative 3 should > > have > > > > the > > > > > > same utility. Setting larger -XX:MaxDirectMemorySize will not > > reduce > > > > the > > > > > > sizes of the other memory pools. > > > > > > > > > > > > If the actual direct memory usage of Task Off-Heap Memory and JVM > > > > > > Overhead potentially exceed 200MB, then > > > > > > > > > > > > - Alternative 2 suffers from frequent OOM. To avoid that, the > > only > > > > > thing > > > > > > user can do is to modify the configuration and increase JVM > > Direct > > > > > > Memory > > > > > > (Task Off-Heap Memory + JVM Overhead). Let's say that user > > > increases > > > > > JVM > > > > > > Direct Memory to 250MB, this will reduce the total size of > other > > > > > memory > > > > > > pools to 750MB, given the total process memory remains 1GB. > > > > > > - For alternative 3, there is no chance of direct OOM. There > are > > > > > chances > > > > > > of exceeding the total process memory limit, but given that > the > > > > > process > > > > > > may > > > > > > not use up all the reserved native memory (Off-Heap Managed > > > Memory, > > > > > > Network > > > > > > Memory, JVM Metaspace), if the actual direct memory usage is > > > > slightly > > > > > > above > > > > > > yet very close to 200MB, user probably do not need to change > the > > > > > > configurations. > > > > > > > > > > > > Therefore, I think from the user's perspective, a feasible > > > > configuration > > > > > > for alternative 2 may lead to lower resource utilization compared > > to > > > > > > alternative 3. > > > > > > > > > > > > Thank you~ > > > > > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > > > > > > > > > On Fri, Aug 16, 2019 at 10:28 AM Till Rohrmann < > > trohrm...@apache.org > > > > > > > > > > wrote: > > > > > > > > > > > > > I guess you have to help me understand the difference between > > > > > > alternative 2 > > > > > > > and 3 wrt to memory under utilization Xintong. > > > > > > > > > > > > > > - Alternative 2: set XX:MaxDirectMemorySize to Task Off-Heap > > Memory > > > > and > > > > > > JVM > > > > > > > Overhead. Then there is the risk that this size is too low > > > resulting > > > > > in a > > > > > > > lot of garbage collection and potentially an OOM. > > > > > > > - Alternative 3: set XX:MaxDirectMemorySize to something larger > > > than > > > > > > > alternative 2. This would of course reduce the sizes of the > other > > > > > memory > > > > > > > types. > > > > > > > > > > > > > > How would alternative 2 now result in an under utilization of > > > memory > > > > > > > compared to alternative 3? If alternative 3 strictly sets a > > higher > > > > max > > > > > > > direct memory size and we use only little, then I would expect > > that > > > > > > > alternative 3 results in memory under utilization. > > > > > > > > > > > > > > Cheers, > > > > > > > Till > > > > > > > > > > > > > > On Tue, Aug 13, 2019 at 4:19 PM Yang Wang < > danrtsey...@gmail.com > > > > > > > > wrote: > > > > > > > > > > > > > > > Hi xintong,till > > > > > > > > > > > > > > > > > > > > > > > > > Native and Direct Memory > > > > > > > > > > > > > > > > My point is setting a very large max direct memory size when > we > > > do > > > > > not > > > > > > > > differentiate direct and native memory. If the direct > > > > > memory,including > > > > > > > user > > > > > > > > direct memory and framework direct memory,could be calculated > > > > > > > > correctly,then > > > > > > > > i am in favor of setting direct memory with fixed value. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Memory Calculation > > > > > > > > > > > > > > > > I agree with xintong. For Yarn and k8s,we need to check the > > > memory > > > > > > > > configurations in client to avoid submitting successfully and > > > > failing > > > > > > in > > > > > > > > the flink master. > > > > > > > > > > > > > > > > > > > > > > > > Best, > > > > > > > > > > > > > > > > Yang > > > > > > > > > > > > > > > > Xintong Song <tonysong...@gmail.com>于2019年8月13日 周二22:07写道： > > > > > > > > > > > > > > > > > Thanks for replying, Till. > > > > > > > > > > > > > > > > > > About MemorySegment, I think you are right that we should > not > > > > > include > > > > > > > > this > > > > > > > > > issue in the scope of this FLIP. This FLIP should > concentrate > > > on > > > > > how > > > > > > to > > > > > > > > > configure memory pools for TaskExecutors, with minimum > > > > involvement > > > > > on > > > > > > > how > > > > > > > > > memory consumers use it. > > > > > > > > > > > > > > > > > > About direct memory, I think alternative 3 may not having > the > > > > same > > > > > > over > > > > > > > > > reservation issue that alternative 2 does, but at the cost > of > > > > risk > > > > > of > > > > > > > > over > > > > > > > > > using memory at the container level, which is not good. My > > > point > > > > is > > > > > > > that > > > > > > > > > both "Task Off-Heap Memory" and "JVM Overhead" are not easy > > to > > > > > > config. > > > > > > > > For > > > > > > > > > alternative 2, users might configure them higher than what > > > > actually > > > > > > > > needed, > > > > > > > > > just to avoid getting a direct OOM. For alternative 3, > users > > do > > > > not > > > > > > get > > > > > > > > > direct OOM, so they may not config the two options > > aggressively > > > > > high. > > > > > > > But > > > > > > > > > the consequences are risks of overall container memory > usage > > > > > exceeds > > > > > > > the > > > > > > > > > budget. > > > > > > > > > > > > > > > > > > Thank you~ > > > > > > > > > > > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Tue, Aug 13, 2019 at 9:39 AM Till Rohrmann < > > > > > trohrm...@apache.org> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > Thanks for proposing this FLIP Xintong. > > > > > > > > > > > > > > > > > > > > All in all I think it already looks quite good. > Concerning > > > the > > > > > > first > > > > > > > > open > > > > > > > > > > question about allocating memory segments, I was > wondering > > > > > whether > > > > > > > this > > > > > > > > > is > > > > > > > > > > strictly necessary to do in the context of this FLIP or > > > whether > > > > > > this > > > > > > > > > could > > > > > > > > > > be done as a follow up? Without knowing all details, I > > would > > > be > > > > > > > > concerned > > > > > > > > > > that we would widen the scope of this FLIP too much > because > > > we > > > > > > would > > > > > > > > have > > > > > > > > > > to touch all the existing call sites of the MemoryManager > > > where > > > > > we > > > > > > > > > allocate > > > > > > > > > > memory segments (this should mainly be batch operators). > > The > > > > > > addition > > > > > > > > of > > > > > > > > > > the memory reservation call to the MemoryManager should > not > > > be > > > > > > > affected > > > > > > > > > by > > > > > > > > > > this and I would hope that this is the only point of > > > > interaction > > > > > a > > > > > > > > > > streaming job would have with the MemoryManager. > > > > > > > > > > > > > > > > > > > > Concerning the second open question about setting or not > > > > setting > > > > > a > > > > > > > max > > > > > > > > > > direct memory limit, I would also be interested why Yang > > Wang > > > > > > thinks > > > > > > > > > > leaving it open would be best. My concern about this > would > > be > > > > > that > > > > > > we > > > > > > > > > would > > > > > > > > > > be in a similar situation as we are now with the > > > > > > RocksDBStateBackend. > > > > > > > > If > > > > > > > > > > the different memory pools are not clearly separated and > > can > > > > > spill > > > > > > > over > > > > > > > > > to > > > > > > > > > > a different pool, then it is quite hard to understand > what > > > > > exactly > > > > > > > > > causes a > > > > > > > > > > process to get killed for using too much memory. This > could > > > > then > > > > > > > easily > > > > > > > > > > lead to a similar situation what we have with the > > > cutoff-ratio. > > > > > So > > > > > > > why > > > > > > > > > not > > > > > > > > > > setting a sane default value for max direct memory and > > giving > > > > the > > > > > > > user > > > > > > > > an > > > > > > > > > > option to increase it if he runs into an OOM. > > > > > > > > > > > > > > > > > > > > @Xintong, how would alternative 2 lead to lower memory > > > > > utilization > > > > > > > than > > > > > > > > > > alternative 3 where we set the direct memory to a higher > > > value? > > > > > > > > > > > > > > > > > > > > Cheers, > > > > > > > > > > Till > > > > > > > > > > > > > > > > > > > > On Fri, Aug 9, 2019 at 9:12 AM Xintong Song < > > > > > tonysong...@gmail.com > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > Thanks for the feedback, Yang. > > > > > > > > > > > > > > > > > > > > > > Regarding your comments: > > > > > > > > > > > > > > > > > > > > > > *Native and Direct Memory* > > > > > > > > > > > I think setting a very large max direct memory size > > > > definitely > > > > > > has > > > > > > > > some > > > > > > > > > > > good sides. E.g., we do not worry about direct OOM, and > > we > > > > > don't > > > > > > > even > > > > > > > > > > need > > > > > > > > > > > to allocate managed / network memory with > > > Unsafe.allocate() . > > > > > > > > > > > However, there are also some down sides of doing this. > > > > > > > > > > > > > > > > > > > > > > - One thing I can think of is that if a task > executor > > > > > > container > > > > > > > is > > > > > > > > > > > killed due to overusing memory, it could be hard for > > use > > > > to > > > > > > know > > > > > > > > > which > > > > > > > > > > > part > > > > > > > > > > > of the memory is overused. > > > > > > > > > > > - Another down side is that the JVM never trigger GC > > due > > > > to > > > > > > > > reaching > > > > > > > > > > max > > > > > > > > > > > direct memory limit, because the limit is too high > to > > be > > > > > > > reached. > > > > > > > > > That > > > > > > > > > > > means we kind of relay on heap memory to trigger GC > > and > > > > > > release > > > > > > > > > direct > > > > > > > > > > > memory. That could be a problem in cases where we > have > > > > more > > > > > > > direct > > > > > > > > > > > memory > > > > > > > > > > > usage but not enough heap activity to trigger the > GC. > > > > > > > > > > > > > > > > > > > > > > Maybe you can share your reasons for preferring > setting a > > > > very > > > > > > > large > > > > > > > > > > value, > > > > > > > > > > > if there are anything else I overlooked. > > > > > > > > > > > > > > > > > > > > > > *Memory Calculation* > > > > > > > > > > > If there is any conflict between multiple configuration > > > that > > > > > user > > > > > > > > > > > explicitly specified, I think we should throw an error. > > > > > > > > > > > I think doing checking on the client side is a good > idea, > > > so > > > > > that > > > > > > > on > > > > > > > > > > Yarn / > > > > > > > > > > > K8s we can discover the problem before submitting the > > Flink > > > > > > > cluster, > > > > > > > > > > which > > > > > > > > > > > is always a good thing. > > > > > > > > > > > But we can not only rely on the client side checking, > > > because > > > > > for > > > > > > > > > > > standalone cluster TaskManagers on different machines > may > > > > have > > > > > > > > > different > > > > > > > > > > > configurations and the client does see that. > > > > > > > > > > > What do you think? > > > > > > > > > > > > > > > > > > > > > > Thank you~ > > > > > > > > > > > > > > > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Aug 8, 2019 at 5:09 PM Yang Wang < > > > > > danrtsey...@gmail.com> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > Hi xintong, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for your detailed proposal. After all the > memory > > > > > > > > configuration > > > > > > > > > > are > > > > > > > > > > > > introduced, it will be more powerful to control the > > flink > > > > > > memory > > > > > > > > > > usage. I > > > > > > > > > > > > just have few questions about it. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - Native and Direct Memory > > > > > > > > > > > > > > > > > > > > > > > > We do not differentiate user direct memory and native > > > > memory. > > > > > > > They > > > > > > > > > are > > > > > > > > > > > all > > > > > > > > > > > > included in task off-heap memory. Right? So i don’t > > think > > > > we > > > > > > > could > > > > > > > > > not > > > > > > > > > > > set > > > > > > > > > > > > the -XX:MaxDirectMemorySize properly. I prefer > leaving > > > it a > > > > > > very > > > > > > > > > large > > > > > > > > > > > > value. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > - Memory Calculation > > > > > > > > > > > > > > > > > > > > > > > > If the sum of and fine-grained memory(network memory, > > > > managed > > > > > > > > memory, > > > > > > > > > > > etc.) > > > > > > > > > > > > is larger than total process memory, how do we deal > > with > > > > this > > > > > > > > > > situation? > > > > > > > > > > > Do > > > > > > > > > > > > we need to check the memory configuration in client? > > > > > > > > > > > > > > > > > > > > > > > > Xintong Song <tonysong...@gmail.com> 于2019年8月7日周三 > > > > 下午10:14写道： > > > > > > > > > > > > > > > > > > > > > > > > > Hi everyone, > > > > > > > > > > > > > > > > > > > > > > > > > > We would like to start a discussion thread on > > "FLIP-49: > > > > > > Unified > > > > > > > > > > Memory > > > > > > > > > > > > > Configuration for TaskExecutors"[1], where we > > describe > > > > how > > > > > to > > > > > > > > > improve > > > > > > > > > > > > > TaskExecutor memory configurations. The FLIP > document > > > is > > > > > > mostly > > > > > > > > > based > > > > > > > > > > > on > > > > > > > > > > > > an > > > > > > > > > > > > > early design "Memory Management and Configuration > > > > > > Reloaded"[2] > > > > > > > by > > > > > > > > > > > > Stephan, > > > > > > > > > > > > > with updates from follow-up discussions both online > > and > > > > > > > offline. > > > > > > > > > > > > > > > > > > > > > > > > > > This FLIP addresses several shortcomings of current > > > > (Flink > > > > > > 1.9) > > > > > > > > > > > > > TaskExecutor memory configuration. > > > > > > > > > > > > > > > > > > > > > > > > > > - Different configuration for Streaming and > Batch. > > > > > > > > > > > > > - Complex and difficult configuration of RocksDB > > in > > > > > > > Streaming. > > > > > > > > > > > > > - Complicated, uncertain and hard to understand. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Key changes to solve the problems can be summarized > > as > > > > > > follows. > > > > > > > > > > > > > > > > > > > > > > > > > > - Extend memory manager to also account for > memory > > > > usage > > > > > > by > > > > > > > > > state > > > > > > > > > > > > > backends. > > > > > > > > > > > > > - Modify how TaskExecutor memory is partitioned > > > > > accounted > > > > > > > > > > individual > > > > > > > > > > > > > memory reservations and pools. > > > > > > > > > > > > > - Simplify memory configuration options and > > > > calculations > > > > > > > > logics. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Please find more details in the FLIP wiki document > > [1]. > > > > > > > > > > > > > > > > > > > > > > > > > > (Please note that the early design doc [2] is out > of > > > > sync, > > > > > > and > > > > > > > it > > > > > > > > > is > > > > > > > > > > > > > appreciated to have the discussion in this mailing > > list > > > > > > > thread.) > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Looking forward to your feedbacks. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thank you~ > > > > > > > > > > > > > > > > > > > > > > > > > > Xintong Song > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > [1] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://cwiki.apache.org/confluence/display/FLINK/FLIP-49%3A+Unified+Memory+Configuration+for+TaskExecutors > > > > > > > > > > > > > > > > > > > > > > > > > > [2] > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://docs.google.com/document/d/1o4KvyyXsQMGUastfPin3ZWeUXWsJgoL7piqp1fFYJvA/edit?usp=sharing > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
