Hi Jun and David, Regarding token bucket vs, Rate behavior. We recently observed a couple of cases where a bursty workload behavior would result in long-ish pauses in between, resulting in lower overall bandwidth than the quota. I will need to debug this a bit more to be 100% sure, but it does look like the case described by David earlier in this thread. So, I agree with Jun -- I think we should make all quota rate behavior consistent, and probably similar to the token bucket one.
Looking at KIP-13, it doesn't describe rate calculation in enough detail, but does mention window size. So, we could keep "window size" and "number of samples" configs and change Rate implementation to be more similar to token bucket: * number of samples define our burst size * Change the behavior, which could be described as: If a burst happens after an idle period, the burst would effectively spread evenly over the (now - window) time period, where window is (<number of samples> - 1)* <window size>. Which basically describes a token bucket, while keeping the current quota configs. I think we can even implement this by changing the way we record the last sample or lastWindowMs. Jun, if we would be changing Rate calculation behavior in bandwidth and request quotas, would we need a separate KIP? Shouldn't need to if we keep window size and number of samples configs, right? Thanks, Anna On Wed, Jun 3, 2020 at 3:24 PM Jun Rao <j...@confluent.io> wrote: > Hi, David, > > Thanks for the reply. > > 11. To match the behavior in the Token bucket approach, I was thinking that > requests that don't fit in the previous time windows will be accumulated in > the current time window. So, the 60 extra requests will be accumulated in > the latest window. Then, the client also has to wait for 12 more secs > before throttling is removed. I agree that this is probably a better > behavior and it's reasonable to change the existing behavior to this one. > > To me, it seems that sample_size * num_windows is the same as max burst > balance. The latter seems a bit better to configure. The thing is that the > existing quota system has already been used in quite a few places and if we > want to change the configuration in the future, there is the migration > cost. Given that, do you feel it's better to adopt the new token bucket > terminology or just adopt the behavior somehow into our existing system? If > it's the former, it would be useful to document this in the rejected > section and add a future plan on migrating existing quota configurations. > > Jun > > > On Tue, Jun 2, 2020 at 6:55 AM David Jacot <dja...@confluent.io> wrote: > > > Hi Jun, > > > > Thanks for your reply. > > > > 10. I think that both options are likely equivalent from an accuracy > point > > of > > view. If we put the implementation aside, conceptually, I am not > convinced > > by the used based approach because resources don't have a clear owner > > in AK at the moment. A topic can be created by (Principal A, no client > id), > > then can be extended by (no principal, Client B), and finally deleted by > > (Principal C, Client C). This does not sound right to me and I fear that > it > > is not going to be easy to grasp for our users. > > > > Regarding the naming, I do agree that we can make it more future proof. > > I propose `controller_mutations_rate`. I think that differentiating the > > mutations > > from the reads is still a good thing for the future. > > > > 11. I am not convinced by your proposal for the following reasons: > > > > First, in my toy example, I used 101 windows and 7 * 80 requests. We > could > > effectively allocate 5 * 100 requests to the previous windows assuming > that > > they are empty. What shall we do with the remaining 60 requests? Shall we > > allocate them to the current window or shall we divide it among all the > > windows? > > > > Second, I don't think that we can safely change the behavior of all the > > existing > > rates used because it actually changes the computation of the rate as > > values > > allocated to past windows would expire before they would today. > > > > Overall, while trying to fit in the current rate, we are going to build a > > slightly > > different version of the rate which will be even more confusing for > users. > > > > Instead, I think that we should embrace the notion of burst as it could > > also > > be applied to other quotas in the future. Users don't have to know that > we > > use the Token Bucket or a special rate inside at the end of the day. It > is > > an > > implementation detail. > > > > Users would be able to define: > > - a rate R; and > > - a maximum burst B. > > > > If we change the metrics to be as follow: > > - the actual rate; > > - the burst balance in %, 0 meaning that the user is throttled; > > It remains disattach from the algorithm. > > > > I personally prefer this over having to define a rate and a number of > > windows > > while having to understand that the number of windows implicitly defines > > the > > allowed burst. I think that it is clearer and easier to grasp. Don't you? > > > > Best, > > David > > > > On Fri, May 29, 2020 at 6:38 PM Jun Rao <j...@confluent.io> wrote: > > > > > Hi, David, Anna, > > > > > > Thanks for the response. Sorry for the late reply. > > > > > > 10. Regarding exposing rate or usage as quota. Your argument is that > > usage > > > is not very accurate anyway and is harder to implement. So, let's just > > be a > > > bit loose and expose rate. I am sort of neutral on that. (1) It seems > to > > me > > > that overall usage will be relatively more accurate than rate. All the > > > issues that Anna brought up seem to exist for rate too. Rate has the > > > additional problem that the cost of each request may not be uniform. > (2) > > In > > > terms of implementation, a usage based approach requires tracking the > > user > > > info through the life cycle of an operation. However, as you mentioned, > > > things like topic creation can generate additional > > > LeaderAndIsr/UpdateMetadata requests. Longer term, we probably want to > > > associate those cost to the user who initiated the operation. If we do > > > that, we sort of need to track the user for the full life cycle of the > > > processing of an operation anyway. (3) If you prefer rate strongly, I > > don't > > > have strong objections. However, I do feel that the new quota name > should > > > be able to cover all controller related cost longer term. This KIP > > > currently only covers topic creation/deletion. It would not be ideal if > > in > > > the future, we have to add yet another type of quota for some other > > > controller related operations. The quota name in the KIP has partition > > > mutation. In the future, if we allow things like topic renaming, it may > > not > > > be related to partition mutation directly and it would be trickier to > fit > > > those operations in the current quota. So, maybe sth more general like > > > controller_operations_quota will be more future proof. > > > > > > 11. Regarding the difference between the token bucket algorithm and our > > > current quota mechanism. That's a good observation. It seems that we > can > > > make a slight change to our current quota mechanism to achieve a > similar > > > thing. As you said, the issue was that we allocate all 7 * 80 requests > in > > > the last 1 sec window in our current mechanism. This is a bit > unintuitive > > > since each sec only has a quota capacity of 5. An alternative way is to > > > allocate the 7 * 80 requests to all previous windows, each up to the > > > remaining quota capacity left. So, you will fill the current 1 sec > window > > > and all previous ones, each with 5. Then, it seems this will give the > > same > > > behavior as token bucket? The reason that I keep asking this is that > from > > > an operational perspective, it's simpler if all types of quotas work in > > the > > > same way. > > > > > > Jun > > > > > > On Tue, May 26, 2020 at 9:52 AM David Jacot <dja...@confluent.io> > wrote: > > > > > > > Hi folks, > > > > > > > > I have updated the KIP. As mentioned by Jun, I have made the > > > > quota per principal/clientid similarly to the other quotas. I have > > > > also explained how this will work in conjunction with the auto > > > > topics creation. > > > > > > > > Please, take a look at it. I plan to call a vote for it in the next > few > > > > days if there are no comments in this thread. > > > > > > > > Best, > > > > David > > > > > > > > On Wed, May 13, 2020 at 10:57 AM Tom Bentley <tbent...@redhat.com> > > > wrote: > > > > > > > > > Hi David, > > > > > > > > > > Thanks for the explanation and confirmation that evolving the APIs > is > > > not > > > > > off the table in the longer term. > > > > > > > > > > Kind regards, > > > > > > > > > > Tom > > > > > > > > > > > > > > >
