> Why not just return > org.apache.kafka.clients.admin.Config like describeConfigs does?
brokers have a `num.partitions` config that does not map to a valid `Config` entry for a topic. another added benefit to using `NewTopic` may be (future kip) having the cluster return the actual replica mappings it would create (i have no idea if this is actually possible) dan On Wed, Dec 13, 2017 at 9:55 AM, Colin McCabe <cmcc...@apache.org> wrote: > On Tue, Dec 12, 2017, at 19:02, Ewen Cheslack-Postava wrote: > > re: API versions, I actually wasn't sure if we needed it or not. I'm fine > > if people would prefer just bumping it, but I was actually curious if we > > could get away without bumping it. I don't know the behavior of the > > broker code paths for this well enough to know what types of errors those > > non-null assertions get converted into. > > There's no advantage to trying to keep the API version number the same, > though. Since we have bidirectional client compatibility now, the > clients and the server will just negotiate whatever version they need. > New clients can still talk to older brokers that don't support this > feature. > > If you don't bump the API version, the best case scenario is that you > get a disconnect exception and the end-user is left confused about why. > The worse-case scenario is that you crash the broker (but probably not, > since you'd just get an NPE in serde, I think). If you bump the version > number, you can provide a proper UnsupportedVersionException when the > feature is not supported. > > > For the return type, NewTopic seems reasonable and kind of intuitive -- > > basically a description of the NewTopic you would get. The only reason I > > would be wary of reusing it is that what we don't want people doing is > > taking that and passing it directly into AdminClient.createTopics since > > we don't want them explicitly overriding all the defaults. > > Yeah. Another thing is that NewTopic has a lot of stuff related to > replication that doesn't seem relevant here. For example, when creating > NewTopic, you have the option of either setting replicationFactor, or > setting up a specific replica assignment. Why not just return > org.apache.kafka.clients.admin.Config like describeConfigs does? > > best, > Colin > > > > > -Ewen > > > > On Tue, Dec 12, 2017 at 2:32 PM, dan <dan.norw...@gmail.com> wrote: > > > > > Colin/Ewen, > > > > > > i will add changes to bump the API version. > > > > > > any preferences on the return type for the new method? tbh it seems > like > > > returning a NewTopic could make sense because the ConfigResource for a > > > TOPIC type does not let me encode `numPartitions` > > > > > > thanks > > > dan > > > > > > On Mon, Dec 11, 2017 at 7:22 PM, Colin McCabe <cmcc...@apache.org> > wrote: > > > > > > > Hi Dan, > > > > > > > > The KIP looks good overall. > > > > > > > > On Mon, Dec 11, 2017, at 18:28, Ewen Cheslack-Postava wrote: > > > > > I think the key point is when the kafka admin and user creating > topics > > > > > differ. I think a more realistic example of Dan's point (2) is for > > > > > retention. I know that realistically, admins aren't just going to > > > > > randomly > > > > > drop the broker defaults from 1w to 1d without warning anyone > (they'd > > > > > likely be fired...). But as a user, I may not know the broker > configs, > > > if > > > > > admins have overridden them, etc. I may want a *minimum* of, e.g., > 2d. > > > > > But if the broker defaults are higher such that the admins are > > > confident > > > > the > > > > > cluster can handle 1w, I'd rather just fall back on the default > value. > > > > > > > > Right. I think this API addresses a similar set of use-cases as > adding > > > > the "validateOnly" boolean for createTopics. You shouldn't have to > > > > create a topic to know whether it was possible to create it, or what > the > > > > retention will end up being, etc. etc. > > > > > > > > > Now, there's arguably a better solution for that case -- allow > topic > > > > > configs to express a *minimum* value (or maximum depending on the > > > > > particular config), with the broker config taking precedence if it > has > > > a > > > > > smaller value (or larger in the case of maximums). This lets you > > > express > > > > > your minimum requirements but allows the cluster to do more if > that's > > > the > > > > > default. However, that would represent a much more significant and > > > > > invasive change, and honestly I think it is more likely to confuse > > > users. > > > > > > > > There always need to be topic defaults, though. If we add a foobar > > > > configuration for topics, existing topics will need to get > grandfathered > > > > in with a default foobar. And they won't be able to set min and max > > > > ranges, because foobars didn't exist back when the old topics were > > > > created. > > > > > > > > > > > > > > @Dan, regarding compatibility, this changes behavior without > revving > > > the > > > > > request version number, which normally we only do for things that > are > > > > > reasonably considered bugfixes or were it has no compatibility > > > > > implications. In this case, older brokers talking to newer > AdminClients > > > > > will presumably return some error. Do we know what the non-null > > > assertion > > > > > gets converted to and if we're happy with the behavior (i.e. will > > > > > applications be able to do something reasonable, distinguish it > from > > > some > > > > > completely unrelated error, etc)? Similarly, it's obviously only > one > > > > > implementation using the KIP-4 APIs, but do we know what > client-side > > > > > validation AdminClient is already doing and whether old > AdminClients > > > > > talking to new brokers will see a change in behavior (or do they do > > > > > client-side validation such that old clients simply wouldn't have > > > access > > > > > to this new functionality)? > > > > > > > > I think we should bump the API version for this or add a new API key. > > > > Nothing good is going to happen by pretending like this is compatible > > > > with existing brokers. > > > > > > > > Also, I think it would be better just to have a separate function in > > > > AdminClient rather than overloading the behavior of NULL in > > > > describeConfigs. It's not really that much more effort to have > another > > > > AdminClient function, and it's a lot simpler for devs to understand > than > > > > magical NULL behavior in describeConfigs. > > > > > > > > best, > > > > Colin > > > > > > > > > > > > > > -Ewen > > > > > > > > > > On Mon, Dec 11, 2017 at 2:11 PM, dan <dan.norw...@gmail.com> > wrote: > > > > > > > > > > > Dong, > > > > > > > > > > > > I agree that it *may* be better for a user to be explicit, > however > > > > there > > > > > > are a couple reasons they may not. > > > > > > 1) a user doesn't even know what the options are. imagine > writing a > > > > tool > > > > > > for users to create topics that steps them through things: > > > > > > > > > > > > $ kafka-topics.sh --create > > > > > > Give your topic a name: my-fav-topic > > > > > > How many partitions do you want [12]: > > > > > > What is the minimum in set replica size [2]: > > > > > > What is the maximum message size [1MB]: > > > > > > ... > > > > > > > > > > > > 2) a user wants to use broker defaults within reason. say they > thinke > > > > they > > > > > > want min.cleanable.dirty.ratio=.5 and the default is .6. maybe > thats > > > > fine, > > > > > > or even better for them. since the person maintaining the actual > > > > cluster > > > > > > has put thought in to this config. and as the maintainer keeps > > > working > > > > on > > > > > > making the cluster run better they can change and tune things on > the > > > > > > cluster level as needed. > > > > > > > > > > > > dan > > > > > > > > > > > > > > > > > > On Wed, Dec 6, 2017 at 11:51 AM, Dong Lin <lindon...@gmail.com> > > > wrote: > > > > > > > > > > > > > Hey Dan, > > > > > > > > > > > > > > I think you are saying that, if user can read the default > config > > > > before > > > > > > > creating the topic, then this user can make better decision in > what > > > > > > configs > > > > > > > need to be overwritten. The question here is, how user is > going to > > > > use > > > > > > this > > > > > > > config to make the decision. > > > > > > > > > > > > > > In my understanding, user will compare the default value with > > > > expected > > > > > > > value, and override the config to be expected value if they are > > > > > > different. > > > > > > > If this is the only way that the default value can affect > user's > > > > > > decision, > > > > > > > then it seems OK for user to directly override the config to > the > > > > expected > > > > > > > value. I am wondering if this solution has some drawback. > > > > > > > > > > > > > > On the other hand, maybe there is a more advanced way that the > > > > default > > > > > > > value can affect the user's decision. It may be useful to > > > understand > > > > this > > > > > > > use-case more specifically. Could you help provide a specific > > > example > > > > > > here? > > > > > > > > > > > > > > Thanks, > > > > > > > Dong > > > > > > > > > > > > > > > > > > > > > On Wed, Dec 6, 2017 at 11:12 AM, dan <dan.norw...@gmail.com> > > > wrote: > > > > > > > > > > > > > > > Rajini, > > > > > > > > > > > > > > > > that was not my intent, the intent was to give a user of > this api > > > > an > > > > > > > > insight in to what their topic will look like once created. > as > > > > things > > > > > > > stand > > > > > > > > now a user is unable to (easily) have any knowledge of what > their > > > > topic > > > > > > > > configs will be before doing a `CREATE_TOPICS`. as i > mentioned in > > > > the > > > > > > > KIP, > > > > > > > > another option would be to have the `CreateTopicsOptions. > > > > > > > > validateOnly=true` > > > > > > > > version return data, but seems more invasive/questionable. > > > > > > > > > > > > > > > > dan > > > > > > > > > > > > > > > > On Wed, Dec 6, 2017 at 5:10 AM, Rajini Sivaram < > > > > > > rajinisiva...@gmail.com> > > > > > > > > wrote: > > > > > > > > > > > > > > > > > Hi Dan, > > > > > > > > > > > > > > > > > > Thank you for the KIP. KIP-226 (https://cwiki.apache.org/ > > > > > > > > > confluence/display/KAFKA/KIP-226+-+Dynamic+Broker+ > > > Configuration) > > > > > > > > proposes > > > > > > > > > to add an option to include all synonyms of a config option > > > when > > > > > > > > describing > > > > > > > > > configs. This includes any defaults. For example (using > Dong's > > > > > > > example), > > > > > > > > if > > > > > > > > > you have topicA with min.cleanable.dirty.ratio=0.6 as an > > > > override and > > > > > > > the > > > > > > > > > broker default is 0.5, AdminClient#describeConfigs with > > > synonyms > > > > > > would > > > > > > > > > return the actual value in use as the config value (I,e. > > > > > > > > > min.cleanable.dirty.ratio=0.6). And the synonyms list > would > > > > contain > > > > > > > (in > > > > > > > > > the > > > > > > > > > order of precedence in which these configs are applied): > > > > > > > > > > > > > > > > > > 1. min.cleanable.dirty.ratio=0.6, config > source=TOPIC_CONFIG > > > > > > > > > 2. log.min.cleanable.dirty.ratio=0.5, config > > > > > > > > > source=STATIC_BROKER_CONFIG > > > > > > > > > > > > > > > > > > > > > > > > > > > KIP-226 doesn't give you exactly what you are proposing in > this > > > > KIP, > > > > > > > but > > > > > > > > it > > > > > > > > > gives the mapping of configs. My concern with this KIP is > that > > > it > > > > > > > assumes > > > > > > > > > that if the broker config is static, i.e. if the current > value > > > of > > > > > > > > > log.min.cleanable.dirty.ratio=0.6, you can safely create a > > > topic > > > > > > with > > > > > > > > > default min.cleanable.dirty.ratio relying on that the > value to > > > be > > > > > > > applied > > > > > > > > > all the time. This will not work with dynamic broker > configs if > > > > the > > > > > > > > broker > > > > > > > > > defaults can be updated at any time. > > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Dec 4, 2017 at 11:22 PM, dan < > dan.norw...@gmail.com> > > > > wrote: > > > > > > > > > > > > > > > > > > > for point 1 i agree, its not too strong. only addition i > > > could > > > > come > > > > > > > up > > > > > > > > > with > > > > > > > > > > is that it allows any utility to have better forwards > > > > > > compatability. > > > > > > > a > > > > > > > > > cli > > > > > > > > > > written that can inspect how a topic will be created > would be > > > > able > > > > > > to > > > > > > > > > give > > > > > > > > > > insight/expectations about configs that didn't exist at > > > > compilation > > > > > > > > time. > > > > > > > > > > > > > > > > > > > > for point 2, i am thinking about a situation where the > user > > > > > > creating > > > > > > > > > topics > > > > > > > > > > and the user managing brokers are different people with > > > > different > > > > > > > > > > skills/abilities. > > > > > > > > > > > > > > > > > > > > so in the given example lets assume a user creating the > topic > > > > does > > > > > > > not > > > > > > > > > > *really* understand what that config means, so they are > > > likely > > > > to > > > > > > > just > > > > > > > > > > leave it as default. and are happy for their admin to > change > > > > these > > > > > > on > > > > > > > > the > > > > > > > > > > broker as needed. > > > > > > > > > > > > > > > > > > > > but say we have another user who is creating a topic who > has > > > > much > > > > > > > more > > > > > > > > > > experience and has done testing, they will be able to > > > determine > > > > > > what > > > > > > > > the > > > > > > > > > > value is on the cluster and check to see if it matches > > > > expectations > > > > > > > or > > > > > > > > > > needs to be set. possibly if this is set to something > > > > incorrect for > > > > > > > > their > > > > > > > > > > usecase they will have a reason to verify and speak with > the > > > > admin > > > > > > > > about > > > > > > > > > > their usecase. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > moreover, i think without this added capability it makes > it > > > > > > > > > > difficult/impossible to accurately use broker defaults > for > > > > topics. > > > > > > > > right > > > > > > > > > > now a user is left to either decide configs a priori and > lose > > > > this > > > > > > > > > > functionality, or guess/check what they need to set and > end > > > in > > > > a > > > > > > > > possibly > > > > > > > > > > bad situation until they can get their *live* topic > > > configured. > > > > > > > > > > > > > > > > > > > > dan > > > > > > > > > > > > > > > > > > > > On Mon, Dec 4, 2017 at 2:50 PM, Dong Lin < > > > lindon...@gmail.com> > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > Hey Dan, > > > > > > > > > > > > > > > > > > > > > > Thanks again for the update:) > > > > > > > > > > > > > > > > > > > > > > I am not sure I fully understand the points (1) and > (2) in > > > > the > > > > > > > > "Always > > > > > > > > > > > Configure ALL Configs For a Topic". In my previous > > > question, > > > > I > > > > > > > don't > > > > > > > > > mean > > > > > > > > > > > that users should specify full list of topics configs. > I > > > mean > > > > > > that > > > > > > > > user > > > > > > > > > > can > > > > > > > > > > > specify the full list of topic configs he/she wants to > > > > override. > > > > > > > > > > > > > > > > > > > > > > Your KIP proposes to allow user to query the default > topic > > > > > > configs. > > > > > > > > In > > > > > > > > > my > > > > > > > > > > > understanding, users want to know the default configs > only > > > if > > > > > > > he/she > > > > > > > > > > > already has a specific list of (config, value) pairs > for > > > > which > > > > > > > he/she > > > > > > > > > > wants > > > > > > > > > > > to override. The workflow will be that user queries the > > > > default > > > > > > > > > configs, > > > > > > > > > > > compares the default value with that specific list, and > > > > > > selectively > > > > > > > > > > > override the configs whose value is different from the > > > > default > > > > > > > value. > > > > > > > > > > > Therefore, the alternative solution does not suffer the > > > > problem > > > > > > (1) > > > > > > > > > > because > > > > > > > > > > > user needs to know that specific list of (config, > value) > > > pair > > > > > > > anyway. > > > > > > > > > > Does > > > > > > > > > > > this make sense? > > > > > > > > > > > > > > > > > > > > > > Regarding problem (2), I think you are saying that if > the > > > > user > > > > > > > wants > > > > > > > > to > > > > > > > > > > set > > > > > > > > > > > the min.cleanable.dirty.ratio to be 0.5 and the default > > > > value is > > > > > > > > > > currently > > > > > > > > > > > set to 0.5, then user would not want to explicitly > override > > > > the > > > > > > > > config > > > > > > > > > > > during topic creation. The purpose is for the > > > > > > > > min.cleanable.dirty.ratio > > > > > > > > > > of > > > > > > > > > > > this topic to be changed to 0.6 if admin change the > default > > > > > > > > > > > min.cleanable.dirty.ratio to 0.6 in the future. > > > > > > > > > > > > > > > > > > > > > > But I am not sure this is a reasonable example. If user > > > > wants to > > > > > > > > > > > compare default value of min.cleanable.dirty.ratio > with its > > > > > > > expected > > > > > > > > > > value > > > > > > > > > > > 0.5, then it seems reasonable for user to override it > to be > > > > 0.5 > > > > > > > > during > > > > > > > > > > > topic creation if the default value is currently 0.6. > The > > > > > > question > > > > > > > > is, > > > > > > > > > > why > > > > > > > > > > > would user not want to override the default value to > be 0.5 > > > > if > > > > > > the > > > > > > > > > > default > > > > > > > > > > > value is changed from 0.5 to 0.6 later? > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > Dong > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Dec 4, 2017 at 2:36 PM, dan < > dan.norw...@gmail.com > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > updated again :) > > > > > > > > > > > > > > > > > > > > > > > > by having users always set all configs you lose the > > > > ability to > > > > > > > use > > > > > > > > > the > > > > > > > > > > > > broker defaults as intended, since topic configs are > > > > overlaid. > > > > > > > > > example > > > > > > > > > > in > > > > > > > > > > > > the kip doc. > > > > > > > > > > > > > > > > > > > > > > > > dan > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Dec 4, 2017 at 11:47 AM, Dong Lin < > > > > lindon...@gmail.com > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > Hey Dan, > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for the update. I just want to push the > > > > discussion a > > > > > > bit > > > > > > > > > > > further. > > > > > > > > > > > > > Another alternative, which currently is not > described > > > in > > > > the > > > > > > > KIP, > > > > > > > > > is > > > > > > > > > > > for > > > > > > > > > > > > > user to always create the topic with the full list > of > > > > configs > > > > > > > it > > > > > > > > > may > > > > > > > > > > > want > > > > > > > > > > > > > to override. Can you help me understand what is the > > > > drawback > > > > > > of > > > > > > > > > this > > > > > > > > > > > > > approach? > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > Dong > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Dec 4, 2017 at 11:30 AM, dan < > > > > dan.norw...@gmail.com> > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > Dong, > > > > > > > > > > > > > > > > > > > > > > > > > > > > i added a section on current state and > workarounds > > > > along > > > > > > with > > > > > > > > my > > > > > > > > > > > > > arguments > > > > > > > > > > > > > > for why they are less than optimal to the wiki. > but > > > the > > > > > > jist > > > > > > > of > > > > > > > > > it > > > > > > > > > > is > > > > > > > > > > > > you > > > > > > > > > > > > > > can end up with messages in your topic in an > > > > > > > incorrect/invalid > > > > > > > > > > state > > > > > > > > > > > if > > > > > > > > > > > > > you > > > > > > > > > > > > > > do this. > > > > > > > > > > > > > > > > > > > > > > > > > > > > thanks, > > > > > > > > > > > > > > dan > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Dec 4, 2017 at 10:53 AM, Dong Lin < > > > > > > > lindon...@gmail.com > > > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hey Dan, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks for the KIP. Can you help me understand > the > > > > > > > motivation > > > > > > > > > by > > > > > > > > > > > > > > providing > > > > > > > > > > > > > > > a use-case that can not be easily completed > without > > > > this > > > > > > > KIP? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > It seems that most users will simply create the > > > topic > > > > > > > without > > > > > > > > > > > > worrying > > > > > > > > > > > > > > > about the default configs. If a user has > specific > > > > > > > requirement > > > > > > > > > for > > > > > > > > > > > the > > > > > > > > > > > > > > > default configs, he/she can use > > > > > > > AdminClient.describeConfigs() > > > > > > > > > and > > > > > > > > > > > > > > > AdminClient.alterConfigs() after the topic has > been > > > > > > > created. > > > > > > > > > This > > > > > > > > > > > > seems > > > > > > > > > > > > > > to > > > > > > > > > > > > > > > work well. Did I miss something? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > > > > > > > > > Dong > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On Mon, Dec 4, 2017 at 9:25 AM, dan < > > > > > > dan.norw...@gmail.com > > > > > > > > > > > > > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I would like to start a discussion about > KIP-234 > > > > > > > > > > > > > > > > https://cwiki.apache.org/ > > > > confluence/display/KAFKA/KIP- > > > > > > > > > > > > > > > > 234%3A+add+support+for+ > > > > getting+topic+defaults+from+ > > > > > > > > > AdminClient > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > thanks > > > > > > > > > > > > > > > > dan > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
