Yeah, Magnus, I'm not arguing for either approach (1) or approach (2), I'm saying the only reason it would make sense to combine the version check and the metadata request would be if the version check was cluster wide like the other metadata. That was where that idea originated and if you make the check per-connection it no longer makes sense, right?
-Jay On Wed, Mar 16, 2016 at 12:36 AM, Magnus Edenhill <mag...@edenhill.se> wrote: > 1. But there is no way of conveying version mismatch in the protocol, that's > one of the reasons for this KIP in the first place :) > Even if there was (e.g., the empty response hack) it makes the client > implementation > more complex since the cached cluster-level version support returned by the > broker > can't really be trusted so then there is an initial "We can probably use > this version" > state followed by a "phew, request succeeded" or "darn, seems the request > wasn't supported" state. > > Additionally these late errors are going to be a problem in some cases, > let's say > a certain client really needs OffsetCommit v9, so it starts a consumer, > processes > a bunch of messages and then attempts to commit the latest processed offset > only to find > broker didnt support v9 thus failing the commit. We then have a situation > where > messages were processed but they can't be committed, thus resulting in > multiple > processing, or likewise. > > Re caching: > A couple of years back we had the discussion on cached cluster ISR info in > the > Metadata response, since the information was cached it couldn't be trusted > and was thus > deemed useless. Let's not make that mistake again. > > Re in Metadata or not: > I'm personally fine with having a specific request to query the current > broker's API support, > the client will fire off both MetadataRequests + ApiQueryRequest back to > back so there is > no latency penalty. This is a cleaner solution and I'm a weak +1 for it > unless other client devs oppose. > > > /Magnus > > > 2016-03-16 0:37 GMT+01:00 Jay Kreps <j...@confluent.io>: > >> Yeah I think there are two possible approaches: >> 1. You get the versions in the metadata request and cache them and >> invalidate that cache if you get a version mismatch error (basically >> as we do with leadership information). >> 2. You check each connection >> >> I think combining metadata request and version check only makes sense >> in (1), right? If it is (2) I don't see how you save anything and the >> requests don't really make sense because you're mixing cluster wide >> state about partitions with info about the answering broker. >> >> -Jay >> >> On Tue, Mar 15, 2016 at 4:25 PM, Magnus Edenhill <mag...@edenhill.se> >> wrote: >> > Hey Jay, >> > >> > as discussed earlier it is not safe to cache/relay a broker's version or >> > its supported API versions, >> > by the time the client connects the broker might have upgraded to another >> > version which effectively >> > makes this information useless in a cached form. >> > >> > The complexity of querying for protocol verion is very implementation >> > dependent and >> > hard to generalize on, I dont foresee any bigger problems adding support >> > for an extra protocol version >> > querying state in librdkafka, but other client devs should chime in. >> > There are already post-connect,pre-operation states for dealing with SSL >> > and SASL. >> > >> > The reason for putting the API versioning stuff in the Metadata request >> is >> > that it is already used >> > for bootstrapping a client and/or connection and thus saves us a >> round-trip >> > (and possibly a state). >> > >> > >> > For how this will be used; I can't speak for other client devs but aim to >> > make a mapping between >> > the features my client exposes to a set of specific APIs and their >> minimum >> > version.. >> > E.g.: Balanced consumer groups requires JoinGroup >= V0, LeaveGroup >= >> V0, >> > SyncGroup >= V0, and so on. >> > If those requirements can be fullfilled then the feature is enabled, >> > otherwise an error is returned to the user. >> > >> > /Magnus >> > >> > >> > 2016-03-15 23:35 GMT+01:00 Jay Kreps <j...@confluent.io>: >> > >> >> Hey Ashish, >> >> >> >> Can you expand in the proposal on how this would be used by clients? >> >> This proposal only has one slot for api versions, though in fact there >> >> is potentially a different version on each broker. I think the >> >> proposal is that every single time the client establishes a connection >> >> it would then need to issue a metadata request on that connection to >> >> check supported versions. Is that correct? >> >> >> >> The point of merging version information with metadata request was >> >> that the client wouldn't have to manage this additional state for each >> >> connection, but rather the broker would gather the information and >> >> give a summary of all brokers in the cluster. (Managing the state >> >> doesn't seem complex but actually since the full state machine for a >> >> request is something like begin connecting=>connection complete=>begin >> >> sending request=>do work sending=>await response=>do work reading >> >> response adding to the state machine around this is not as simple as >> >> it seems...you can see the code in the java client around this). >> >> >> >> It sounds like in this proposal you are proposing merging with the >> >> metadata request but not summarizing across the cluster? Can you >> >> explain the thinking vs a separate request? >> >> >> >> It would really be good if the KIP can summarize the whole interaction >> >> and how clients will work. >> >> >> >> -Jay >> >> >> >> On Tue, Mar 15, 2016 at 3:24 PM, Ashish Singh <asi...@cloudera.com> >> wrote: >> >> > Magnus and I had a brief discussion following the KIP call. KIP-35 >> >> > < >> >> >> https://cwiki.apache.org/confluence/display/KAFKA/KIP-35+-+Retrieving+protocol+version >> >> > >> >> > wiki has been updated accordingly. Please review the KIP and vote on >> the >> >> > corresponding vote thread. >> >> > >> >> > On Mon, Mar 14, 2016 at 11:27 PM, Ashish Singh <asi...@cloudera.com> >> >> wrote: >> >> > >> >> >> I think there is a bit of misunderstanding going on here regarding >> >> >> protocol documentation and its versioning. It could be that I am the >> one >> >> >> who misunderstood it, please correct me if so. >> >> >> >> >> >> Taking Gwen's example. >> >> >> >> >> >> 1. 0.10.0 (protocol v4) is released with current KIP-35 >> >> >> 2. On trunk, modify produce requests and bump to v5 >> >> >> 3. On trunk, we modify metadata requests and bump to v6 >> >> >> 4. Now we decide that the metadata change fixes a super critical >> issue >> >> and >> >> >> want to backport the change. What's the protocol version of the next >> >> >> release of 0.10.0 - which supports v6 protocol only partially? >> >> >> >> >> >> As per my understanding, this will be v7. When we say a broker is on >> >> >> ApiVersion 7, we do not necessarily mean that it also supports >> >> ApiVersion >> >> >> up to v7. A broker on ApiVersion v7 should probably mean, please >> refer >> >> v7 >> >> >> of protocol documentation to find out supported protocol versions of >> >> this >> >> >> broker. >> >> >> >> >> >> I just added an example on the KIP wiki to elaborate more on protocol >> >> >> documentation versioning. Below is the excerpt. >> >> >> >> >> >> For instance say we have two brokers, BrokerA has ApiVersion 4 and >> >> BrokerB >> >> >> has ApiVersion 5. This means we should have protocol documentations >> for >> >> >> ApiVersions 4 and 5. Say we have the following as protocol >> documentation >> >> >> for these two versions. >> >> >> >> >> >> Sample Protocol Documentation V4 >> >> >> Version: 4 // Comes from ApiVersion >> >> >> REQ_A_0: ... >> >> >> REQ_A_1: ... >> >> >> RESP_A_0: ... >> >> >> RESP_A_1: ... >> >> >> >> >> >> Sample Protocol Documentation V5 >> >> >> Version: 5 // Comes from ApiVersion >> >> >> REQ_A_1: ... >> >> >> REQ_A_2: ... >> >> >> RESP_A_1: ... >> >> >> RESP_A_2: ... >> >> >> >> >> >> All a client needs to know to be able to successfully communicate >> with a >> >> >> broker is what is the supported ApiVersion of the broker. Say via >> some >> >> >> mechanism, discussed below, client gets to know that BrokerA has >> >> ApiVersion >> >> >> 4 and BrokerB has ApiVersion 5. With that information, and the >> available >> >> >> protocol documentations for those ApiVersions client can deduce what >> >> >> protocol versions does the broker supports. In this case client will >> >> deduce >> >> >> that it can use v0 and v1 of REQ_A and RESP_A while talking to >> BrokerA, >> >> >> while it can use v1 and v2 of REQ_A and RESP_A while talking to >> BrokerB. >> >> >> >> >> >> On Mon, Mar 14, 2016 at 10:50 PM, Ewen Cheslack-Postava < >> >> e...@confluent.io >> >> >> > wrote: >> >> >> >> >> >>> Yeah, Gwen's example is a good one. And it doesn't even have to be >> >> thought >> >> >>> of in terms of the implementation -- you can think of the protocol >> >> itself >> >> >>> as effectively being possible to branch and have changes >> cherry-picked. >> >> >>> Given the way some changes interact and that only some may be >> feasible >> >> to >> >> >>> backport, this may be important. >> >> >>> >> >> >>> Similarly, it's difficult to make that definition . In practice, we >> >> >>> sometimes branch and effectively merge the protocol -- i.e. we >> develop >> >> 2 >> >> >>> KIPs with independent changes at the same time. If you force a >> linear >> >> >>> model, you also *force* the ordering of implementation, which will >> be a >> >> >>> pretty serious constraint in a lot of cases. Two protocol-changing >> KIPs >> >> >>> may >> >> >>> occur near in time, but one may be a much larger change. >> >> >>> >> >> >>> Finally, it might be worth noting that from a client developer's >> >> >>> perspective, the linear order may not be all that intuitive when we >> >> pile >> >> >>> on >> >> >>> a bunch of protocol changes in one release. They probably don't >> >> actually >> >> >>> care about that global protocol version. They'll care more about the >> >> types >> >> >>> of things Dana was talking about previously: LZ4 support (which >> isn't >> >> even >> >> >>> a protocol change, but an important feature clients might need to >> know >> >> >>> about!), Kafka-backed offset storage (requires 2 protocol changes), >> >> etc. >> >> >>> While we want to encourage supporting all features, we should be >> >> realistic >> >> >>> about how client developers tackle feature development and limited >> >> >>> bandwidth. They are probably more feature driven than version >> driven. >> >> >>> >> >> >>> This is what Gwen was saying I had mentioned. The idea of features >> is >> >> >>> actually separate from what has been described so far and *does* >> >> require a >> >> >>> mapping to protocol versions, but also allows you to capture more >> than >> >> >>> that >> >> >>> and at more flexible granularity (single request type protocol >> version >> >> >>> bump >> >> >>> or the whole set of requests could change). The idea isn't quite the >> >> same >> >> >>> as browser feature detection, but that's my frame of reference for >> it >> >> (see >> >> >>> https://developer.mozilla.org/en-US/docs/Browser_Feature_Detection >> ), >> >> the >> >> >>> process of trying to sort out supported features and protocols >> based on >> >> >>> browser version IDs (sort of equivalent to broker implementation >> >> versions >> >> >>> here) is a huge mess. Going entirely the other route (say, only >> >> enabling a >> >> >>> feature in CSS3 if *all* CSS3 features are implemented) is really >> >> >>> restrictive. >> >> >>> >> >> >>> I don't have a concrete proposal right now, but something like >> >> "features" >> >> >>> that sit somewhere between a global protocol version number and only >> >> >>> individual request versions more accurately captures what we want to >> >> >>> express, in my opinion. >> >> >>> >> >> >>> -Ewen >> >> >>> >> >> >>> On Mon, Mar 14, 2016 at 6:45 PM, Gwen Shapira <g...@confluent.io> >> >> wrote: >> >> >>> >> >> >>> > Jay, >> >> >>> > >> >> >>> > Ewen had a good example: >> >> >>> > >> >> >>> > 1. 0.10.0 (protocol v4) is released with current KIP-35 >> >> >>> > 2. On trunk, modify produce requests and bump to v5 >> >> >>> > 3. On trunk, we modify metadata requests and bump to v6 >> >> >>> > 4. Now we decide that the metadata change fixes a super critical >> >> issue >> >> >>> and >> >> >>> > want to backport the change. What's the protocol version of the >> next >> >> >>> > release of 0.10.0 - which supports v6 protocol only partially? >> >> >>> > >> >> >>> > Gwen >> >> >>> > >> >> >>> > On Mon, Mar 14, 2016 at 6:38 PM, Jay Kreps <j...@confluent.io> >> wrote: >> >> >>> > >> >> >>> > > Hey Dana, >> >> >>> > > >> >> >>> > > I am actually thinking about it differently. Basically I think >> you >> >> are >> >> >>> > > imagining a world in which the Kafka code is the source of >> truth, >> >> and >> >> >>> > > the Kafka developers make random changes that inflict pain on >> you >> >> at >> >> >>> > > will. The protocol documentation is basically just some >> >> semi-accurate >> >> >>> > > description of what the code does. It sounds like this isn't too >> >> far >> >> >>> > > from the actual world. :-) In that world I agree that the best >> we >> >> >>> > > could do would be to assign some id to versions (the md5 of the >> >> Kafka >> >> >>> > > jar, maybe) and put in various checks around that in clients to >> >> try to >> >> >>> > > keep things working. >> >> >>> > > >> >> >>> > > But imagine a different approach where we try to really treat >> the >> >> >>> > > protocol as a document and treat that as the source of truth. We >> >> try >> >> >>> > > to make this document cover what is and isn't specified and >> make it >> >> >>> > > cover enough to support client implementations and a given Kafka >> >> >>> > > version covers some range of protocols explicitly. There is a >> >> version >> >> >>> > > of this document for each protocol version. The code implements >> the >> >> >>> > > protocol rather than vice versa. >> >> >>> > > >> >> >>> > > So in other words protocol changes are totally ordered and >> separate >> >> >>> > > from code development (we might develop them together but the >> >> protocol >> >> >>> > > assignment would come when you checked in the new protocol >> version >> >> >>> > > which would happen with your code). >> >> >>> > > >> >> >>> > > This was really the intention with the protocol originally >> (though >> >> we >> >> >>> > > were doing it on a per-api basis), but I think that >> understanding >> >> was >> >> >>> > > not shared by the full team and we have not done a great job of >> >> >>> > > important things like documentation or explaining how this are >> >> >>> > > supposed to work so we fall back on the "the protocol is >> whatever >> >> the >> >> >>> > > code does" thing. >> >> >>> > > >> >> >>> > > Does that make sense? In that sense think one of the more >> important >> >> >>> > > things we could get out of this would not be more versioning >> >> features >> >> >>> > > so much as clear docs and processes around protocol versioning. >> >> >>> > > >> >> >>> > > -Jay >> >> >>> > > >> >> >>> > > On Mon, Mar 14, 2016 at 6:22 PM, Dana Powers < >> >> dana.pow...@gmail.com> >> >> >>> > > wrote: >> >> >>> > > > Is a linear protocol int consistent with the current release >> >> model? >> >> >>> It >> >> >>> > > > seems like that would break down w/ the multiple release >> branches >> >> >>> that >> >> >>> > > are >> >> >>> > > > all simultaneously maintained? Or is it implicit that no patch >> >> >>> release >> >> >>> > > can >> >> >>> > > > ever bump the protocol int? Or maybe the protocol int gets >> some >> >> >>> extra >> >> >>> > > > "wiggle" on minor / major releases to create unallocated >> version >> >> >>> ints >> >> >>> > > that >> >> >>> > > > could be used on future patch releases / backports? >> >> >>> > > > >> >> >>> > > > I think the protocol version int does make sense for folks >> >> deploying >> >> >>> > from >> >> >>> > > > trunk. >> >> >>> > > > >> >> >>> > > > -Dana >> >> >>> > > > >> >> >>> > > > On Mon, Mar 14, 2016 at 6:13 PM, Jay Kreps <j...@confluent.io> >> >> >>> wrote: >> >> >>> > > > >> >> >>> > > >> Yeah I think that is the point--we have a proposal for a new >> >> >>> protocol >> >> >>> > > >> versioning scheme and a vote on it but it doesn't actually >> >> describe >> >> >>> > > >> how versioning will work yet! I gave my vague impression >> based >> >> on >> >> >>> this >> >> >>> > > >> thread, but I want to make sure that is correct and get it >> >> written >> >> >>> > > >> down before we adopt it. >> >> >>> > > >> >> >> >>> > > >> -Jay >> >> >>> > > >> >> >> >>> > > >> On Mon, Mar 14, 2016 at 5:58 PM, Gwen Shapira < >> >> g...@confluent.io> >> >> >>> > > wrote: >> >> >>> > > >> > On Mon, Mar 14, 2016 at 5:31 PM, Jay Kreps < >> j...@confluent.io> >> >> >>> > wrote: >> >> >>> > > >> > >> >> >>> > > >> >> Couple of missing things: >> >> >>> > > >> >> >> >> >>> > > >> >> This KIP doesn't have a proposal on versioning it just >> gives >> >> >>> > > different >> >> >>> > > >> >> options, it'd be good to get a concrete proposal in the >> KIP. >> >> >>> Here >> >> >>> > is >> >> >>> > > my >> >> >>> > > >> >> understanding of what we are proposing (can someone sanity >> >> check >> >> >>> > and >> >> >>> > > if >> >> >>> > > >> >> correct, update the kip): >> >> >>> > > >> >> >> >> >>> > > >> >> 1. We will augment the existing api_version field in >> the >> >> >>> header >> >> >>> > > with >> >> >>> > > >> a >> >> >>> > > >> >> protocol_version that will begin at some initial value >> and >> >> >>> > > increment >> >> >>> > > >> by >> >> >>> > > >> >> 1 >> >> >>> > > >> >> every time we make a changes to any of the api_versions >> >> >>> > (question: >> >> >>> > > >> >> including internal apis?). >> >> >>> > > >> >> >> >> >>> > > >> > >> >> >>> > > >> > Jay, this part was not in the KIP and was never discussed. >> >> >>> > > >> > Are you proposing adding this? Or is it just an assumption >> you >> >> >>> made? >> >> >>> > > >> > >> >> >>> > > >> > >> >> >>> > > >> > >> >> >>> > > >> >> 2. The protocol_version will be added to the metadata >> >> request >> >> >>> > > >> >> 3. We will also add a string that this proposal is >> calling >> >> >>> > > >> VersionString >> >> >>> > > >> >> which will describe the build of kafka in some way. The >> >> >>> clients >> >> >>> > > >> should >> >> >>> > > >> >> not >> >> >>> > > >> >> under any circumstances do anything with this string >> other >> >> >>> than >> >> >>> > > >> print it >> >> >>> > > >> >> out to the user. >> >> >>> > > >> >> >> >> >>> > > >> >> One thing I'm not sure about: I think currently metadata >> >> sits in >> >> >>> > the >> >> >>> > > >> client >> >> >>> > > >> >> for 10 mins by default. Say a client bootstraps and then a >> >> >>> server >> >> >>> > is >> >> >>> > > >> >> downgraded to an earlier version, won't the client's >> metadata >> >> >>> > version >> >> >>> > > >> >> indicate that that client handles a version it doesn't >> >> actually >> >> >>> > > handle >> >> >>> > > >> any >> >> >>> > > >> >> more? We need to document how clients will handle this. >> >> >>> > > >> >> >> >> >>> > > >> >> Here are some comments on other details: >> >> >>> > > >> >> >> >> >>> > > >> >> 1. As a minor thing I think we should avoid naming the >> >> fields >> >> >>> > > >> VersionId >> >> >>> > > >> >> and VersionString which sort of implies they are both >> used >> >> >>> for >> >> >>> > > >> >> versioning. >> >> >>> > > >> >> I think we should call them something like >> ProtocolVersion >> >> >>> and >> >> >>> > > >> >> BuildDescription, with BuildDescription being totally >> >> >>> > unspecified >> >> >>> > > >> other >> >> >>> > > >> >> than that it is some kind of human readable string >> >> >>> describing a >> >> >>> > > >> >> particular >> >> >>> > > >> >> Kafka build. We really don't want a client attempting >> to >> >> use >> >> >>> > this >> >> >>> > > >> >> string in >> >> >>> > > >> >> any way as that would always be the wrong thing to do >> in >> >> the >> >> >>> > > >> versioning >> >> >>> > > >> >> scheme we are proposing, you should always use the >> >> protocol >> >> >>> > > version. >> >> >>> > > >> >> 2. Does making the topics field in the metadata request >> >> >>> nullable >> >> >>> > > >> >> actually make sense? We have a history of wanting to >> add >> >> >>> magical >> >> >>> > > >> values >> >> >>> > > >> >> rather than fields. Currently topics=[a] means give me >> >> >>> > information >> >> >>> > > >> about >> >> >>> > > >> >> topic a, topics=[] means give me information about all >> >> >>> topics, >> >> >>> > > and we >> >> >>> > > >> >> are >> >> >>> > > >> >> proposing topics=null would mean don't give me topics. >> I >> >> >>> don't >> >> >>> > > have a >> >> >>> > > >> >> strong opinion. >> >> >>> > > >> >> 3. I prefer Jason's proposal on using a conservative >> >> metadata >> >> >>> > > version >> >> >>> > > >> >> versus the empty response hack. However I think that >> may >> >> >>> > actually >> >> >>> > > >> >> exacerbate the downgrade scenario I described. >> >> >>> > > >> >> 4. I agree with Jason that we should really look at the >> >> >>> details >> >> >>> > of >> >> >>> > > >> the >> >> >>> > > >> >> implementation so we know it works--implementing server >> >> >>> support >> >> >>> > > >> without >> >> >>> > > >> >> actually trying it is kind of risky. >> >> >>> > > >> >> >> >> >>> > > >> >> As a meta comment: I'd really like to encourage us to >> think >> >> of >> >> >>> the >> >> >>> > > >> protocol >> >> >>> > > >> >> as a document that includes the following things: >> >> >>> > > >> >> >> >> >>> > > >> >> - The binary format, error codes, etc >> >> >>> > > >> >> - The request/response interaction >> >> >>> > > >> >> - The semantics of each request in different cases >> >> >>> > > >> >> - Instructions on how to use this to implement a client >> >> >>> > > >> >> >> >> >>> > > >> >> This document is versioned with the protocol number and is >> >> the >> >> >>> > > source of >> >> >>> > > >> >> truth for the protocol. >> >> >>> > > >> >> >> >> >>> > > >> >> Part of any protocol change needs to be an update to the >> >> >>> > > instructions on >> >> >>> > > >> >> how to use that part of the protocol. We should be >> >> opinionated. >> >> >>> If >> >> >>> > > there >> >> >>> > > >> >> are two options there should be a reason, and then we >> need to >> >> >>> > > document >> >> >>> > > >> both >> >> >>> > > >> >> and say exactly when to use each. >> >> >>> > > >> >> >> >> >>> > > >> >> I think we also need to get a "how to" document on >> protocol >> >> >>> changes >> >> >>> > > >> just so >> >> >>> > > >> >> people know what they need to do to add a new protocol >> >> feature. >> >> >>> > > >> >> >> >> >>> > > >> >> -Jay >> >> >>> > > >> >> >> >> >>> > > >> >> On Mon, Mar 14, 2016 at 4:51 PM, Jason Gustafson < >> >> >>> > ja...@confluent.io >> >> >>> > > > >> >> >>> > > >> >> wrote: >> >> >>> > > >> >> >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > Are you suggesting this as a solution for the problem >> >> where >> >> >>> a >> >> >>> > > KIP-35 >> >> >>> > > >> >> > aware >> >> >>> > > >> >> > > client sends a higher version of metadata req, say v2, >> >> to a >> >> >>> > > KIP-35 >> >> >>> > > >> >> aware >> >> >>> > > >> >> > > broker that only supports up to v1. >> >> >>> > > >> >> > >> >> >>> > > >> >> > >> >> >>> > > >> >> > Yes, that's right. In that case, the client first sends >> v1, >> >> >>> finds >> >> >>> > > out >> >> >>> > > >> >> that >> >> >>> > > >> >> > the broker supports v2, and then sends v2 (if it has any >> >> >>> reason >> >> >>> > to >> >> >>> > > do >> >> >>> > > >> >> so). >> >> >>> > > >> >> > >> >> >>> > > >> >> > We had a bit of discussion on such scenarios, and it >> >> seemed to >> >> >>> > be a >> >> >>> > > >> >> chicken >> >> >>> > > >> >> > > and egg problem that is hard to avoid. Your suggestion >> >> >>> > definitely >> >> >>> > > >> makes >> >> >>> > > >> >> > > sense, however it falls under the purview of clients. >> >> >>> > > >> >> > >> >> >>> > > >> >> > >> >> >>> > > >> >> > That basically means clients should figure it out for >> >> >>> themselves? >> >> >>> > > >> Might >> >> >>> > > >> >> be >> >> >>> > > >> >> > nice to have a better answer. >> >> >>> > > >> >> > >> >> >>> > > >> >> > KIP-35 only aims on adding support for getting the >> version >> >> >>> info >> >> >>> > > from a >> >> >>> > > >> >> > > broker. This definitely can be utilized by our >> clients. >> >> >>> > However, >> >> >>> > > >> that >> >> >>> > > >> >> can >> >> >>> > > >> >> > > follow KIP-35 changes. Does this sound reasonable to >> you? >> >> >>> > > >> >> > >> >> >>> > > >> >> > >> >> >>> > > >> >> > It may be OK, but I'm a little concerned about offering >> a >> >> >>> feature >> >> >>> > > >> that we >> >> >>> > > >> >> > don't support ourselves. Sometimes it's not until >> >> >>> implementation >> >> >>> > > that >> >> >>> > > >> we >> >> >>> > > >> >> > find out whether it really works as expected. And if >> we're >> >> >>> > > eventually >> >> >>> > > >> >> > planning to support it, I feel we should think through >> >> some of >> >> >>> > the >> >> >>> > > >> cases >> >> >>> > > >> >> a >> >> >>> > > >> >> > bit more. For example, the upgrade and downgrade cases >> that >> >> >>> > Becket >> >> >>> > > >> >> > mentioned earlier. It doesn't feel too great to support >> >> this >> >> >>> > > feature >> >> >>> > > >> >> unless >> >> >>> > > >> >> > we can offer guidance on how to use it. >> >> >>> > > >> >> > >> >> >>> > > >> >> > -Jason >> >> >>> > > >> >> > >> >> >>> > > >> >> > >> >> >>> > > >> >> > >> >> >>> > > >> >> > On Mon, Mar 14, 2016 at 4:20 PM, Ashish Singh < >> >> >>> > asi...@cloudera.com >> >> >>> > > > >> >> >>> > > >> >> wrote: >> >> >>> > > >> >> > >> >> >>> > > >> >> > > Hi Jason, >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > On Mon, Mar 14, 2016 at 4:04 PM, Jason Gustafson < >> >> >>> > > >> ja...@confluent.io> >> >> >>> > > >> >> > > wrote: >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > > Perhaps clients should always send the oldest >> version >> >> of >> >> >>> the >> >> >>> > > >> metadata >> >> >>> > > >> >> > > > request which supports KIP-35 when initially >> >> connecting to >> >> >>> > the >> >> >>> > > >> >> cluster. >> >> >>> > > >> >> > > > Depending on the versions in the response, it can >> >> upgrade >> >> >>> to >> >> >>> > a >> >> >>> > > >> more >> >> >>> > > >> >> > > recent >> >> >>> > > >> >> > > > version. Then maybe we don't need the empty response >> >> hack? >> >> >>> > > >> >> > > > >> >> >>> > > >> >> > > Are you suggesting this as a solution for the problem >> >> where >> >> >>> a >> >> >>> > > KIP-35 >> >> >>> > > >> >> > aware >> >> >>> > > >> >> > > client sends a higher version of metadata req, say v2, >> >> to a >> >> >>> > > KIP-35 >> >> >>> > > >> >> aware >> >> >>> > > >> >> > > broker that only supports up to v1. >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > We had a bit of discussion on such scenarios, and it >> >> seemed >> >> >>> to >> >> >>> > > be a >> >> >>> > > >> >> > chicken >> >> >>> > > >> >> > > and egg problem that is hard to avoid. Your suggestion >> >> >>> > definitely >> >> >>> > > >> makes >> >> >>> > > >> >> > > sense, however it falls under the purview of clients. >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > > >> >> >>> > > >> >> > > > One thing that's not clear to me is whether the >> >> ultimate >> >> >>> goal >> >> >>> > > of >> >> >>> > > >> this >> >> >>> > > >> >> > KIP >> >> >>> > > >> >> > > > is to have our clients support multiple broker >> >> versions. >> >> >>> It >> >> >>> > > would >> >> >>> > > >> be >> >> >>> > > >> >> a >> >> >>> > > >> >> > > > little weird to have this feature if our own clients >> >> don't >> >> >>> > use >> >> >>> > > it. >> >> >>> > > >> >> > > > >> >> >>> > > >> >> > > KIP-35 only aims on adding support for getting the >> >> version >> >> >>> info >> >> >>> > > >> from a >> >> >>> > > >> >> > > broker. This definitely can be utilized by our >> clients. >> >> >>> > However, >> >> >>> > > >> that >> >> >>> > > >> >> can >> >> >>> > > >> >> > > follow KIP-35 changes. Does this sound reasonable to >> you? >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > > >> >> >>> > > >> >> > > > -Jason >> >> >>> > > >> >> > > > >> >> >>> > > >> >> > > > On Mon, Mar 14, 2016 at 3:34 PM, Ashish Singh < >> >> >>> > > >> asi...@cloudera.com> >> >> >>> > > >> >> > > wrote: >> >> >>> > > >> >> > > > >> >> >>> > > >> >> > > > > On Mon, Mar 14, 2016 at 2:12 PM, Ismael Juma < >> >> >>> > > ism...@juma.me.uk >> >> >>> > > >> > >> >> >>> > > >> >> > > wrote: >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > > On Mon, Mar 14, 2016 at 8:45 PM, Gwen Shapira < >> >> >>> > > >> g...@confluent.io >> >> >>> > > >> >> > >> >> >>> > > >> >> > > > wrote: >> >> >>> > > >> >> > > > > > > >> >> >>> > > >> >> > > > > > > > I don't see how it helps. If the client is >> >> >>> > > communicating >> >> >>> > > >> >> with a >> >> >>> > > >> >> > > > > broker >> >> >>> > > >> >> > > > > > > that >> >> >>> > > >> >> > > > > > > > does not support KIP-35, that broker will >> >> simply >> >> >>> > close >> >> >>> > > the >> >> >>> > > >> >> > > > > connection. >> >> >>> > > >> >> > > > > > If >> >> >>> > > >> >> > > > > > > > the broker supports KIP-35, then it will >> >> provide >> >> >>> the >> >> >>> > > >> broker >> >> >>> > > >> >> > > > version. >> >> >>> > > >> >> > > > > I >> >> >>> > > >> >> > > > > > > > don't envisage a scenario where a broker >> does >> >> not >> >> >>> > > support >> >> >>> > > >> >> > KIP-35, >> >> >>> > > >> >> > > > but >> >> >>> > > >> >> > > > > > > > implements the new behaviour of sending an >> >> empty >> >> >>> > > >> response. Do >> >> >>> > > >> >> > > you? >> >> >>> > > >> >> > > > > > > > >> >> >>> > > >> >> > > > > > > > Are you sure about that? Per KIP-35, the >> broker >> >> >>> > > supplies >> >> >>> > > >> the >> >> >>> > > >> >> > > > version >> >> >>> > > >> >> > > > > in >> >> >>> > > >> >> > > > > > > response to Metadata request, not in response >> to >> >> >>> > anything >> >> >>> > > >> else. >> >> >>> > > >> >> > > > > > > If the client sends producer request version >> 42 >> >> >>> > > >> (accidentally >> >> >>> > > >> >> or >> >> >>> > > >> >> > > due >> >> >>> > > >> >> > > > to >> >> >>> > > >> >> > > > > > > premature upgrade) to KIP-35-compactible >> broker >> >> - we >> >> >>> > > want to >> >> >>> > > >> >> see >> >> >>> > > >> >> > an >> >> >>> > > >> >> > > > > empty >> >> >>> > > >> >> > > > > > > packet and not a connection close. >> >> >>> > > >> >> > > > > > > Sending a broker version was deemed >> impractical >> >> >>> IIRC. >> >> >>> > > >> >> > > > > > > >> >> >>> > > >> >> > > > > > >> >> >>> > > >> >> > > > > > OK, so this is a different case than the one >> Ashish >> >> >>> > > described >> >> >>> > > >> >> > > ("client >> >> >>> > > >> >> > > > > that >> >> >>> > > >> >> > > > > > wants to support broker versions that do not >> >> provide >> >> >>> > broker >> >> >>> > > >> >> version >> >> >>> > > >> >> > > in >> >> >>> > > >> >> > > > > > metadata and broker versions that provides >> version >> >> >>> info >> >> >>> > in >> >> >>> > > >> >> > > metadata"). >> >> >>> > > >> >> > > > > So, >> >> >>> > > >> >> > > > > > you are suggesting that if a client is >> >> communicating >> >> >>> > with a >> >> >>> > > >> >> broker >> >> >>> > > >> >> > > that >> >> >>> > > >> >> > > > > > implements KIP-35 and it receives an empty >> >> response, >> >> >>> it >> >> >>> > > will >> >> >>> > > >> >> assume >> >> >>> > > >> >> > > > that >> >> >>> > > >> >> > > > > > the broker doesn't support the request version >> and >> >> it >> >> >>> > won't >> >> >>> > > >> try >> >> >>> > > >> >> to >> >> >>> > > >> >> > > > parse >> >> >>> > > >> >> > > > > > the response? I think it would be good to >> explain >> >> this >> >> >>> > > kind of >> >> >>> > > >> >> > thing >> >> >>> > > >> >> > > in >> >> >>> > > >> >> > > > > > detail in the KIP. >> >> >>> > > >> >> > > > > > >> >> >>> > > >> >> > > > > Actually even in this case and the case I >> mentioned, >> >> >>> > closing >> >> >>> > > >> >> > connection >> >> >>> > > >> >> > > > > should be fine. Lets think about possible reasons >> >> that >> >> >>> > could >> >> >>> > > >> lead >> >> >>> > > >> >> to >> >> >>> > > >> >> > > this >> >> >>> > > >> >> > > > > issue. >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > 1. Client has incorrect mapping of supported >> >> protocols >> >> >>> for >> >> >>> > a >> >> >>> > > >> broker >> >> >>> > > >> >> > > > > version. >> >> >>> > > >> >> > > > > 2. Client misread broker version from metadata >> >> response. >> >> >>> > > >> >> > > > > 3. Client constructed unsupported protocol >> version by >> >> >>> > > mistake. >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > In all the above cases irrespective of what broker >> >> does, >> >> >>> > > client >> >> >>> > > >> >> will >> >> >>> > > >> >> > > keep >> >> >>> > > >> >> > > > > sending wrong request version. >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > At this point, I think sending an empty packet >> >> instead >> >> >>> of >> >> >>> > > >> closing >> >> >>> > > >> >> > > > > connection is a nice to have and not mandatory >> >> >>> requirement. >> >> >>> > > >> Like in >> >> >>> > > >> >> > the >> >> >>> > > >> >> > > > > above case, a client can catch parsing error and >> be >> >> sure >> >> >>> > that >> >> >>> > > >> there >> >> >>> > > >> >> > is >> >> >>> > > >> >> > > > > something wrong in the protocol version it is >> >> sending. >> >> >>> > > However, >> >> >>> > > >> a >> >> >>> > > >> >> > > generic >> >> >>> > > >> >> > > > > connection close does not really provide any >> >> >>> information on >> >> >>> > > >> >> probable >> >> >>> > > >> >> > > > cause. >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > What do you guys suggest? >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > > >> >> >>> > > >> >> > > > > > Ismael >> >> >>> > > >> >> > > > > > >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > -- >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > > Regards, >> >> >>> > > >> >> > > > > Ashish >> >> >>> > > >> >> > > > > >> >> >>> > > >> >> > > > >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > -- >> >> >>> > > >> >> > > >> >> >>> > > >> >> > > Regards, >> >> >>> > > >> >> > > Ashish >> >> >>> > > >> >> > > >> >> >>> > > >> >> > >> >> >>> > > >> >> >> >> >>> > > >> >> >> >>> > > >> >> >>> > >> >> >>> >> >> >>> >> >> >>> >> >> >>> -- >> >> >>> Thanks, >> >> >>> Ewen >> >> >>> >> >> >> >> >> >> >> >> >> >> >> >> -- >> >> >> >> >> >> Regards, >> >> >> Ashish >> >> >> >> >> > >> >> > >> >> > >> >> > -- >> >> > >> >> > Regards, >> >> > Ashish >> >> >>
