[infinispan-dev] Distributed Counter Discussion
Bela Ban
bban at redhat.com
Tue Mar 22 13:12:06 EDT 2016
On 22/03/16 18:04, Dan Berindei wrote:
> On Mon, Mar 21, 2016 at 1:43 PM, Bela Ban <bban at redhat.com> wrote:
>>
>>
>> On 21/03/16 11:12, Pedro Ruivo wrote:
>>> Hi all,
>>>
>>> @Eric, thanks for the requirements.
>>>
>>> @Bela, does JGroups counter supports that semantics (AP)?
>>
>> No. You'd have to catch the MergeView and do this manually.
>
> I should also mention that you don't get a "cluster split" event. With
> when a cluster ABC splits into A and BC and merges back, you could get
> quite a view sequence like this:
>
> A, B, C: A|3 [A, B, C]
> A: A|4 [A, B]
> A: A|5 [A] (could be missing)
How's that possible? Are you assuming that A still gets heartbeats from B?
Otherwise A will definitely get a singleton view A|5=[A], unless the
cluster heals in the meantime (before B is suspected and excluded).
Note that A|4 on A may or may not be received; if FD_ALL is used then
chances are view [A] will be received directly after [ABC] on A.
> B, C: B|4 [B, C]
> A, B, C: B|6 [B, C, A] (merge view)
Note that you could keep the order if you installed a custom
view/merge-view creation policy, but by default members are sorted
according to the UUIDs.
> So it's not that easy to keep track of counter additions "since the split".
Agreed.
>>> Infinispan does not have eventually consistency (yet) neither an update log. So, it
>>> can't reconcile the counter and you will lose one of the partition updates.
>>
>> Same for the JGroups counter service. The jgroups-raft CounterService
>> provides strong consistency, but at the expense of availability.
>>
>>> On 03/18/2016 02:19 PM, Eric Wittmann wrote:
>>>> Agreed. :)
>>>>
>>>> On 3/18/2016 9:31 AM, Bela Ban wrote:
>>>>> So actually you don't care if you have multiple counters in case of a
>>>>> network split, but you do care that the numbers of different counters
>>>>> get reconciled when a network partition heals.
>>>>>
>>>>> Example
>>>>> - C1: 1000
>>>>> - Network split: C1: 1000, C2: 1000
>>>>> - Different clients update counters on both sides of the partition: C1:
>>>>> 1500 C2: 1600
>>>>> - Network split disappears, reconciling C1 to 2100: 1000 +500 +600. This
>>>>> means the 500 added to C1 should have been added to C2 as well, and the
>>>>> 600 to C2 should have been added to C1
>>>>>
>>>>> If such a behavior would be acceptable, then we could do without CP and
>>>>> live with AP
>>>>>
>>>>> On 18/03/16 14:19, Eric Wittmann wrote:
>>>>>> Yes, precisely. The API Gateway itself is clustered. It services a
>>>>>> large volume of inbound traffic which it reverse-proxies to appropriate
>>>>>> back-end APIs after applying policies such as security, rate limiting,
>>>>>> caching, etc.
>>>>>>
>>>>>> -Eric
>>>>>>
>>>>>> On 3/18/2016 2:32 AM, Bela Ban wrote:
>>>>>>> Stupid question: whay do you need a distributed counter for this? Is the
>>>>>>> service you're monitoring replicated in a cluster?
>>>>>>>
>>>>>>> On 17/03/16 18:06, Eric Wittmann wrote:
>>>>>>>> Greetings. Apologies for coming in a bit late on this conversation.
>>>>>>>> Tristan pointed me to it a couple of days ago and unfortunately I'm just
>>>>>>>> now getting time to reply.
>>>>>>>>
>>>>>>>> I can try to quickly give an overview of apiman's (JBoss API Management
>>>>>>>> Gateway) requirements.
>>>>>>>>
>>>>>>>> What we're trying to do is implement support for Limiting policies:
>>>>>>>>
>>>>>>>> * Rate Limiting/Throttling (e.g. limit of 100 requests per second)
>>>>>>>> * Quotas (e.g. limit of 100,000,000 requests per month)
>>>>>>>> * Transfer Quotas (e.g. limit of 2.5GB of data downloaded per day)
>>>>>>>>
>>>>>>>> We will need to support multiple backing implementations of the Rate
>>>>>>>> Limiter, and we're trying to get Infinispan to be one of those
>>>>>>>> implementations.
>>>>>>>>
>>>>>>>> In no particular order, we would need the following characteristics:
>>>>>>>>
>>>>>>>> - Can be "squishy" for quotas and transfer quotas: If you
>>>>>>>> get 100,001,017 requests that's OK
>>>>>>>> - Strict would be cool as an option: Hard-fail when the
>>>>>>>> counter reaches the limit - no chance it will go over.
>>>>>>>> - Lots of individual counters: users may publish 100s of
>>>>>>>> APIs to the Gateway, and each API may be consumed by
>>>>>>>> 100s or 1000s of users/client. Depending on configuration
>>>>>>>> of the policy, *each* user/client has a separate limit.
>>>>>>>> - Counters need to be created dynamically: users can
>>>>>>>> add APIs via the Management UI, configure them to add
>>>>>>>> policies (e.g. a Quota policy) and then publish them to
>>>>>>>> a running Gateway, at which point end users can invoke
>>>>>>>> the API through the Gateway, which will use a counter
>>>>>>>> to enforce the Quota.
>>>>>>>> - Counter values reset at the end of a time boundary: for
>>>>>>>> example, at the end of the month the counter value for
>>>>>>>> the example quota above would reset to 0.
>>>>>>>> - Don't care (right now) what the counter value is: at the
>>>>>>>> moment we simply need to know if some counter max value
>>>>>>>> has been reached. In the future we would like to know
>>>>>>>> when a max value is being "approached" (e.g. to notify a
>>>>>>>> user)
>>>>>>>> - Should be persistent: it would not be ideal for e.g. per-
>>>>>>>> month quota values to be lost on server restart.
>>>>>>>>
>>>>>>>> That's all the high level requirements I can think of off the top of my
>>>>>>>> head, and after reading all of the current messages in this thread. :)
>>>>>>>>
>>>>>>>> -Eric
>>>>>>>> _______________________________________________
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>>>>>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>>>>>>>
>>>>>>>
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>>>>>
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>>
>> --
>> Bela Ban, JGroups lead (http://www.jgroups.org)
>>
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--
Bela Ban, JGroups lead (http://www.jgroups.org)
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