It was originally designed that the framework vs. task memory are
distinguished by whether the memory owned by the slots. We have not
emphasized this in user documents because the dynamic slot allocation is
not yet available to the users, thus they do not need to worry about
whether the memory is owned by slots.
It's against intuition IMO that a memory pool configured via
`t.m.network.*` is actually subtracted from `t.m.framework.off-heap.*`.
Thank you~
Xintong Song
On Tue, Mar 9, 2021 at 5:28 PM Guowei Ma <guowei....@gmail.com> wrote:
> Hi, all
>
> Thanks all for your suggestions and feedback.
> I think it is a good idea that we increase the default size of the
> separated pool by testing. I am fine with adding the suffix(".size") to the
> config name, which makes it more clear to the user.
> But I am a little worried about adding a prefix("framework") because
> currently the tm shuffle service is only a shuffle-plugin, which is not a
> part of the framework. So maybe we could add a clear explanation in the
> document?
>
> Best,
> Guowei
>
>
> On Tue, Mar 9, 2021 at 3:58 PM 曹英杰(北牧) <kevin....@alibaba-inc.com> wrote:
>
>> Thanks for the suggestions. I will do some tests and share the results
>> after the implementation is ready. Then we can give a proper default value.
>>
>> Best,
>> Yingjie
>>
>> ------------------------------------------------------------------
>> 发件人：Till Rohrmann<trohrm...@apache.org>
>> 日 期：2021年03月05日 23:03:10
>> 收件人：Stephan Ewen<se...@apache.org>
>> 抄 送：dev<dev@flink.apache.org>; user<u...@flink.apache.org>; Xintong Song<
>> tonysong...@gmail.com>; 曹英杰(北牧)<kevin....@alibaba-inc.com>; Guowei Ma<
>> guowei....@gmail.com>
>> 主 题：Re: [DISCUSSION] Introduce a separated memory pool for the TM merge
>> shuffle
>>
>> Thanks for this proposal Guowei. +1 for it.
>>
>> Concerning the default size, maybe we can run some experiments and see
>> how the system behaves with different pool sizes.
>>
>> Cheers,
>> Till
>>
>> On Fri, Mar 5, 2021 at 2:45 PM Stephan Ewen <se...@apache.org> wrote:
>>
>>> Thanks Guowei, for the proposal.
>>>
>>> As discussed offline already, I think this sounds good.
>>>
>>> One thought is that 16m sounds very small for a default read buffer
>>> pool. How risky do you think it is to increase this to 32m or 64m?
>>>
>>> Best,
>>> Stephan
>>>
>>> On Fri, Mar 5, 2021 at 4:33 AM Guowei Ma <guowei....@gmail.com> wrote:
>>>
>>>> Hi, all
>>>>
>>>>
>>>> In the Flink 1.12 we introduce the TM merge shuffle. But the
>>>> out-of-the-box experience of using TM merge shuffle is not very good. The
>>>> main reason is that the default configuration always makes users encounter
>>>> OOM [1]. So we hope to introduce a managed memory pool for TM merge shuffle
>>>> to avoid the problem.
>>>> Goals
>>>>
>>>> 1. Don't affect the streaming and pipelined-shuffle-only batch
>>>> setups.
>>>> 2. Don't mix memory with different life cycle in the same pool.
>>>> E.g., write buffers needed by running tasks and read buffer needed even
>>>> after tasks being finished.
>>>> 3. User can use the TM merge shuffle with default memory
>>>> configurations. (May need further tunings for performance optimization,
>>>> but
>>>> should not fail with the default configurations.)
>>>>
>>>> Proposal
>>>>
>>>> 1. Introduce a configuration
>>>> `taskmanager.memory.network.batch-read` to specify the size of this
>>>> memory
>>>> pool. The default value is 16m.
>>>> 2. Allocate the pool lazily. It means that the memory pool would be
>>>> allocated when the TM merge shuffle is used at the first time.
>>>> 3. This pool size will not be add up to the TM's total memory size,
>>>> but will be considered part of
>>>> `taskmanager.memory.framework.off-heap.size`. We need to check that the
>>>> pool size is not larger than the framework off-heap size, if TM merge
>>>> shuffle is enabled.
>>>>
>>>>
>>>> In this default configuration, the allocation of the memory pool is
>>>> almost impossible to fail. Currently the default framework’s off-heap
>>>> memory is 128m, which is mainly used by Netty. But after we introduced zero
>>>> copy, the usage of it has been reduced, and you can refer to the detailed
>>>> data [2].
>>>> Known Limitation
>>>> Usability for increasing the memory pool size
>>>>
>>>> In addition to increasing `taskmanager.memory.network.batch-read`, the
>>>> user may also need to adjust `taskmanager.memory.framework.off-heap.size`
>>>> at the same time. It also means that once the user forgets this, it is
>>>> likely to fail the check when allocating the memory pool.
>>>>
>>>>
>>>> So in the following two situations, we will still prompt the user to
>>>> increase the size of `framework.off-heap.size`.
>>>>
>>>> 1. `taskmanager.memory.network.batch-read` is bigger than
>>>> `taskmanager.memory.framework.off-heap.size`
>>>> 2. Allocating the pool encounters the OOM.
>>>>
>>>>
>>>> An alternative is that when the user adjusts the size of the memory
>>>> pool, the system automatically adjusts it. But we are not entierly sure
>>>> about this, given its implicity and complicating the memory configurations.
>>>> Potential memory waste
>>>>
>>>> In the first step, the memory pool will not be released once allocated.
>>>> This
>>>> means in the first step, even if there is no subsequent batch job, the
>>>> pooled memory cannot be used by other consumers.
>>>>
>>>>
>>>> We are not releasing the pool in the first step due to the concern that
>>>> frequently allocating/deallocating the entire pool may increase the GC
>>>> pressue. Investitations on how to dynamically release the pool when it's no
>>>> longer needed is considered a future follow-up.
>>>>
>>>>
>>>> Looking forward to your feedback.
>>>>
>>>>
>>>>
>>>> [1] https://issues.apache.org/jira/browse/FLINK-20740
>>>>
>>>> [2] https://github.com/apache/flink/pull/7368.
>>>> Best,
>>>> Guowei
>>>>
>>>
>>
