Hello Xiangying,
On Thu, Dec 7, 2023 at 6:32 AM Xiangying Meng <xiangy...@apache.org> wrote: > Hi Girish, > > What you are actually opposing is the implementation of true topic-level > geo-replication. You believe that topics should be divided into different > namespaces based on replication. Following this line of thought, what we > should do is restrict the current topic-level replication settings, not > allowing the replication clusters set at the topic level to exceed the > range of replication clusters set in the namespace. > Yes, that's my viewpoint. In case that's not your view point, then in your use cases do you ever have more than one namespace inside a tenant? With every property coming at topic level, it makes no sense for the namespace hierarchy to exist anymore. > > One point that confuses me is that we provide a setting for topic-level > replication clusters, but it can only be used to amend the namespace > settings and cannot work independently. Isn't this also a poor design for > Pulsar? > This feature was originally added in pulsar without a PIP. And the PR [0] also doesn't have much context around why it was needed and why it is being added.. So I can't comment on why this was added.. But my understanding is that even in a situation when the topics are divided into proper namespaces based on use cases and suddenly there is an exceptional need for one of the existing topics to have lesser replication, then instead of following a long exercise of moving that topic to a new namespace, you can use this feature. [0] - https://github.com/apache/pulsar/pull/12136 > > On Thu, Dec 7, 2023 at 2:28 AM Girish Sharma <scrapmachi...@gmail.com> > wrote: > > > Hello, replies inline. > > > > On Wed, Dec 6, 2023 at 5:28 PM Xiangying Meng <xiangy...@apache.org> > > wrote: > > > > > Hi Girish, > > > > > > Thank you for your explanation. Because Joe's email referenced the > > current > > > implementation of Pulsar, I misunderstood him to be saying that this > > > current implementation is not good. > > > > > > A possible use case is where there is one or a small number of topics > in > > > the namespace that store important messages, which need to be > replicated > > to > > > other clusters. Meanwhile, other topics only need to store data in the > > > local cluster. > > > > > > > Is it not possible to simply have the other topics in a namespace which > > allows for that other cluster, and the local topics remain in the > namespace > > with local cluster needs. Seems to me like a proper use case of two > > different namespaces as the use case is different in both cases. > > > > > > > > > > > > For example, only topic1 needs replication, while topic2 to topic100 do > > > not. According to the current implementation, we need to set > replication > > > clusters at the namespace level (e.g. cluster1 and cluster2), and then > > set > > > the topic-level replication clusters (cluster1) for topic2 to topic100 > to > > > exclude them. It's hard to say that this is a good design. > > > > > > > No, all you need is to put topic1 in namespace1 and topic2 to topic100 in > > namespace2 . This is exactly what me and Joe were saying is a bad design > > choice that you are clubbing all 100 topics in same namespace. > > > > > > > > > > > > Best regards. > > > > > > On Wed, Dec 6, 2023 at 12:49 PM Joe F <joefranc...@gmail.com> wrote: > > > > > > > Girish, > > > > > > > > Thank you for making my point much better than I did .. > > > > > > > > -Joe > > > > > > > > On Tue, Dec 5, 2023 at 1:45 AM Girish Sharma < > scrapmachi...@gmail.com> > > > > wrote: > > > > > > > > > Hello Xiangying, > > > > > > > > > > I believe what Joe here is referring to as "application design" is > > not > > > > the > > > > > design of pulsar or namespace level replication but the design of > > your > > > > > application and the dependency that you've put on topic level > > > > replication. > > > > > > > > > > In general, I am aligned with Joe from an application design > > > standpoint. > > > > A > > > > > namespace is supposed to represent a single application use case, > > topic > > > > > level override of replication clusters helps in cases where there > > are a > > > > few > > > > > exceptional topics which do not need replication in all of the > > > namespace > > > > > clusters. This helps in saving network bandwidth, storage, CPU, RAM > > etc > > > > > > > > > > But the reason why you've raised this PIP is to bring down the > actual > > > > > replication semantics at a topic level. Yes, namespace level still > > > exists > > > > > as per your PIP as well, but is basically left only to be a > "default > > in > > > > > case topic level is missing". > > > > > This brings me to a very basic question - What's the use case that > > you > > > > are > > > > > trying to solve that needs these changes? Because, then what's > > stopping > > > > us > > > > > from bringing every construct that's at a namespace level > (bundling, > > > > > hardware affinity, etc) down to a topic level? > > > > > > > > > > Regards > > > > > > > > > > On Tue, Dec 5, 2023 at 2:52 PM Xiangying Meng < > xiangy...@apache.org> > > > > > wrote: > > > > > > > > > > > Hi Joe, > > > > > > > > > > > > You're correct. The initial design of the replication policy > leaves > > > > room > > > > > > for improvement. To address this, we aim to refine the cluster > > > settings > > > > > at > > > > > > the namespace level in a way that won't impact the existing > system. > > > The > > > > > > replication clusters should solely be used to establish full mesh > > > > > > replication for that specific namespace, without having any other > > > > > > definitions or functionalities. > > > > > > > > > > > > BR, > > > > > > Xiangying > > > > > > > > > > > > > > > > > > On Mon, Dec 4, 2023 at 1:52 PM Joe F <joefranc...@gmail.com> > > wrote: > > > > > > > > > > > > > >if users want to change the replication policy for > > > > > > > topic-n and do not change the replication policy of other > topics, > > > > they > > > > > > need > > > > > > > to change all the topic policy under this namespace. > > > > > > > > > > > > > > This PIP unfortunately flows from attempting to solve bad > > > > application > > > > > > > design > > > > > > > > > > > > > > A namespace is supposed to represent an application, and the > > > > namespace > > > > > > > policy is an umbrella for a similar set of policies that > applies > > > to > > > > > all > > > > > > > topics. The exceptions would be if a topic had a need for a > > > deficit, > > > > > The > > > > > > > case of one topic in the namespace sticking out of the > namespace > > > > policy > > > > > > > umbrella is bad application design in my opinion > > > > > > > > > > > > > > -Joe. > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Sun, Dec 3, 2023 at 6:00 PM Xiangying Meng < > > > xiangy...@apache.org> > > > > > > > wrote: > > > > > > > > > > > > > > > Hi Rajan and Girish, > > > > > > > > Thanks for your reply. About the question you mentioned, > there > > is > > > > > some > > > > > > > > information I want to share with you. > > > > > > > > >If anyone wants to setup different replication clusters then > > > > either > > > > > > > > >those topics can be created under different namespaces or > > > defined > > > > at > > > > > > > topic > > > > > > > > >level policy. > > > > > > > > > > > > > > > > >And users can anyway go and update the namespace's cluster > > list > > > to > > > > > add > > > > > > > the > > > > > > > > >missing cluster. > > > > > > > > Because the replication clusters also mean the clusters where > > the > > > > > topic > > > > > > > can > > > > > > > > be created or loaded, the topic-level replication clusters > can > > > only > > > > > be > > > > > > > the > > > > > > > > subset of namespace-level replication clusters. > > > > > > > > Just as Girish mentioned, the users can update the > namespace's > > > > > cluster > > > > > > > list > > > > > > > > to add the missing cluster. > > > > > > > > But there is a problem because the replication clusters as > the > > > > > > namespace > > > > > > > > level will create a full mesh replication for that namespace > > > across > > > > > the > > > > > > > > clusters defined in > > > > > > > > replication-clusters if users want to change the replication > > > policy > > > > > for > > > > > > > > topic-n and do not change the replication policy of other > > topics, > > > > > they > > > > > > > need > > > > > > > > to change all the topic policy under this namespace. > > > > > > > > > > > > > > > > > Pulsar is being used by many legacy systems and changing > its > > > > > > > > >semantics for specific usecases without considering > > consequences > > > > are > > > > > > > > >creating a lot of pain and incompatibility problems for > other > > > > > existing > > > > > > > > >systems and let's avoid doing it as we are struggling with > > such > > > > > > changes > > > > > > > > and > > > > > > > > >breaking compatibility or changing semantics are just not > > > > > acceptable. > > > > > > > > > > > > > > > > This proposal will not introduce an incompatibility problem, > > > > because > > > > > > the > > > > > > > > default value of the namespace policy of allowed-clusters and > > > > > > > > topic-policy-synchronized-clusters are the > > replication-clusters. > > > > > > > > > > > > > > > > >Allowed clusters defined at tenant level > > > > > > > > >will restrict tenants to create namespaces in > regions/clusters > > > > where > > > > > > > they > > > > > > > > >are not allowed. > > > > > > > > >As Rajan also mentioned, allowed-clusters field has a > > different > > > > > > > > meaning/purpose. > > > > > > > > > > > > > > > > Allowed clusters defined at the tenant level will restrict > > > tenants > > > > > from > > > > > > > > creating namespaces in regions/clusters where they are not > > > allowed. > > > > > > > > Similarly, the allowed clusters defined at the namespace > level > > > will > > > > > > > > restrict the namespace from creating topics in > regions/clusters > > > > where > > > > > > > they > > > > > > > > are not allowed. > > > > > > > > What's wrong with this? > > > > > > > > > > > > > > > > Regards, > > > > > > > > Xiangying > > > > > > > > > > > > > > > > On Fri, Dec 1, 2023 at 2:35 PM Girish Sharma < > > > > > scrapmachi...@gmail.com> > > > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi Xiangying, > > > > > > > > > > > > > > > > > > Shouldn't the solution to the issue mentioned in #21564 [0] > > > > mostly > > > > > be > > > > > > > > > around validating that topic level replication clusters are > > > > subset > > > > > of > > > > > > > > > namespace level replication clusters? > > > > > > > > > It would be a completely compatible change as even today > the > > > case > > > > > > > where a > > > > > > > > > topic has a cluster not defined in namespaces's > > > > > replication-clusters > > > > > > > > > doesn't really work. > > > > > > > > > And users can anyway go and update the namespace's cluster > > list > > > > to > > > > > > add > > > > > > > > the > > > > > > > > > missing cluster. > > > > > > > > > > > > > > > > > > As Rajan also mentioned, allowed-clusters field has a > > different > > > > > > > > > meaning/purpose. > > > > > > > > > Regards > > > > > > > > > > > > > > > > > > On Thu, Nov 30, 2023 at 10:56 AM Xiangying Meng < > > > > > > xiangy...@apache.org> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > Hi, Pulsar Community > > > > > > > > > > > > > > > > > > > > I drafted a proposal to make the configuration of > clusters > > at > > > > the > > > > > > > > > namespace > > > > > > > > > > level clearer. This helps solve the problem of > > > geo-replication > > > > > not > > > > > > > > > working > > > > > > > > > > correctly at the topic level. > > > > > > > > > > > > > > > > > > > > https://github.com/apache/pulsar/pull/21648 > > > > > > > > > > > > > > > > > > > > I'm looking forward to hearing from you. > > > > > > > > > > > > > > > > > > > > BR > > > > > > > > > > Xiangying > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > Girish Sharma > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > Girish Sharma > > > > > > > > > > > > > > > > > > -- > > Girish Sharma > > > -- Girish Sharma
