Hi Tom, That's a good question. As the validation does not create any load on the controller, I was planning to do it without checking the quota at all. Does that sound reasonable?
Best, David On Thu, Jun 4, 2020 at 4:23 PM David Jacot <dja...@confluent.io> wrote: > Hi Jun and Anna, > > Thank you both for your replies. > > Based on our recent discussion, I agree that using a rate is better to > remain > consistent with other quotas. As you both suggested, it seems that changing > the way we compute the rate to better handle spiky workloads and behave a > bit more similarly to the token bucket algorithm makes sense for all > quotas as > well. > > I will update the KIP to reflect this. > > Anna, I think that we can explain this in this KIP. We can't just say that > the Rate > will be updated in this KIP. I think that we need to give a bit more info. > > Best, > David > > On Thu, Jun 4, 2020 at 6:31 AM Anna Povzner <a...@confluent.io> wrote: > >> 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 >> > > > > > >> > > > > >> > > > >> > > >> > >> >
