Hi Colin, Thank you for the updated KIP.
wrt. Request and Response Headers v1, where do you plan to put the optional fields? You mention that all the Requests and Responses will start with a tagged field buffer. Is it for that purpose? Best, David On Mon, Aug 19, 2019 at 7:27 AM Satish Duggana <satish.dugg...@gmail.com> wrote: > Please read struct type as a complex record type in my earlier mail. > The complex type seems to be defined as Schema[1] in the protocol > types. > > 1. > https://github.com/apache/kafka/blob/trunk/clients/src/main/java/org/apache/kafka/common/protocol/types/Schema.java#L27 > > > On Mon, Aug 19, 2019 at 9:46 AM Satish Duggana <satish.dugg...@gmail.com> > wrote: > > > > Sorry! Colin, I may not have been clear in my earlier query about > > optional field type restriction. It is mentioned in one of your > > replies "optional fields are serialized starting with their total > > length". This brings the question of whether optional fields support > > struct types (with or without array values). It seems struct types are > > currently not serialized with total length. I may be missing something > > here. > > > > Thanks, > > Satish. > > > > > > On Wed, Aug 14, 2019 at 8:03 AM Satish Duggana <satish.dugg...@gmail.com> > wrote: > > > > > > Hi Colin, > > > Thanks for the KIP. Optional fields and var length encoding support is > a great > > > improvement for the protocol. > > > > > > >>Optional fields can have any type, except that they cannot be arrays. > > > Note that the restriction against having tagged arrays is just to > simplify > > > serialization. We can relax this restriction in the future without > changing > > > the protocol on the wire. > > > > > > Can an Optional field have a struct type which internally contains an > array > > > field at any level? > > > > > > Thanks, > > > Satish. > > > > > > > > > > > > On Tue, Aug 13, 2019 at 11:49 PM David Jacot <dja...@confluent.io> > wrote: > > > > > > > > Hi Colin, > > > > > > > > Thank you for the KIP! Things are well explained!. It is huge > improvement > > > > for the Kafka protocol. I have few comments on the proposal: > > > > > > > > 1. The interleaved tag/length header sounds like a great > optimisation as it > > > > would be shorter on average. The downside, as > > > > you already pointed out, is that it makes the decoding and the specs > more > > > > complex. Personally, I would also favour using two > > > > vaints in this particular case to keep things simple. > > > > > > > > 2. As discussed, I wonder if it would make sense to extend to KIP to > also > > > > support optional fields in the Record Header. I think > > > > that it could be interesting to have such capability for common > fields > > > > across all the requests or responses (e.g. tracing id). > > > > > > > > Regards, > > > > David > > > > > > > > > > > > > > > > On Tue, Aug 13, 2019 at 10:00 AM Jason Gustafson <ja...@confluent.io> > wrote: > > > > > > > > > > Right, I was planning on doing exactly that for all the > auto-generated > > > > > RPCs. For the manual RPCs, it would be a lot of work. It’s > probably a > > > > > better use of time to convert the manual ones to auto gen first > (with the > > > > > possible exception of Fetch/Produce, where the ROI may be higher > for the > > > > > manual work) > > > > > > > > > > Yeah, that makes sense. Maybe we can include the version bump for > all RPCs > > > > > in this KIP, but we can implement it lazily as the protocols are > converted. > > > > > > > > > > -Jason > > > > > > > > > > On Mon, Aug 12, 2019 at 7:16 PM Colin McCabe <cmcc...@apache.org> > wrote: > > > > > > > > > > > On Mon, Aug 12, 2019, at 11:22, Jason Gustafson wrote: > > > > > > > Hi Colin, > > > > > > > > > > > > > > Thanks for the KIP! This is a significant improvement. One of > my > > > > > personal > > > > > > > interests in this proposal is solving the compatibility > problems we > > > > > have > > > > > > > with the internal schemas used to define consumer offsets and > > > > > transaction > > > > > > > metadata. Currently we have to guard schema bumps with the > inter-broker > > > > > > > protocol format. Once the format is bumped, there is no way to > > > > > downgrade. > > > > > > > By fixing this, we can potentially begin using the new schemas > before > > > > > the > > > > > > > IBP is bumped while still allowing downgrade. > > > > > > > > > > > > > > There are a surprising number of other situations we have > encountered > > > > > > this > > > > > > > sort of problem. We have hacked around it in special cases by > allowing > > > > > > > nullable fields to the end of the schema, but this is not > really an > > > > > > > extensible approach. I'm looking forward to having a better > option. > > > > > > > > > > > > Yeah, this problem keeps coming up. > > > > > > > > > > > > > > > > > > > > With that said, I have a couple questions on the proposal: > > > > > > > > > > > > > > 1. For each request API, we need one version bump to begin > support for > > > > > > > "flexible versions." Until then, we won't have the option of > using > > > > > tagged > > > > > > > fields even if the broker knows how to handle them. Does it > make sense > > > > > to > > > > > > > go ahead and do a universal bump of each request API now so > that we'll > > > > > > have > > > > > > > this option going forward? > > > > > > > > > > > > Right, I was planning on doing exactly that for all the > auto-generated > > > > > > RPCs. For the manual RPCs, it would be a lot of work. It’s > probably a > > > > > > better use of time to convert the manual ones to auto gen first > (with the > > > > > > possible exception of Fetch/Produce, where the ROI may be higher > for the > > > > > > manual work) > > > > > > > > > > > > > 2. The alternating length/tag header encoding lets us save a > byte in > > > > > the > > > > > > > common case. The downside is that it's a bit more complex to > specify. > > > > > It > > > > > > > also has some extra cost if the length exceeds the tag > substantially. > > > > > > > Basically we'd have to pad the tag, right? I think I'm > wondering if we > > > > > > > should just bite the bullet and use two varints instead. > > > > > > > > > > > > That’s a fair point. It would be shorter on average, but worse > for some > > > > > > exceptional cases. Also, the decoding would be more complex, > which might > > > > > be > > > > > > a good reason to go for just having two varints. Yeah, let’s > simplify. > > > > > > > > > > > > Regards, > > > > > > Colin > > > > > > > > > > > > > > > > > > > > Thanks, > > > > > > > Jason > > > > > > > > > > > > > > > > > > > > > On Fri, Aug 9, 2019 at 4:31 PM Colin McCabe < > cmcc...@apache.org> > > > > > wrote: > > > > > > > > > > > > > > > Hi all, > > > > > > > > > > > > > > > > I've made some updates to this KIP. Specifically, I wanted > to avoid > > > > > > > > including escape bytes in the serialization format, since it > was too > > > > > > > > complex. Also, I think this is a good opportunity to slim > down our > > > > > > > > variable length fields. > > > > > > > > > > > > > > > > best, > > > > > > > > Colin > > > > > > > > > > > > > > > > > > > > > > > > On Thu, Jul 11, 2019, at 20:52, Colin McCabe wrote: > > > > > > > > > On Tue, Jul 9, 2019, at 15:29, Jose Armando Garcia Sancio > wrote: > > > > > > > > > > Thanks Colin for the KIP. For my own edification why are > we doing > > > > > > this > > > > > > > > > > "Optional fields can have any type, except for an array > of > > > > > > > > structures."? > > > > > > > > > > Why can't we have an array of structures? > > > > > > > > > > > > > > > > > > Optional fields are serialized starting with their total > length. > > > > > This > > > > > > > > > is straightforward to calculate for primitive fields like > INT32, > > > > > (or > > > > > > > > > even an array of INT32), but more difficult to calculate > for an > > > > > array > > > > > > > > > of structures. Basically, we'd have to do a two-pass > serialization > > > > > > > > > where we first calculate the lengths of everything, and > then write > > > > > it > > > > > > > > > out. > > > > > > > > > > > > > > > > > > The nice thing about this KIP is that there's nothing in > the > > > > > protocol > > > > > > > > > stopping us from adding support for this feature in the > future. We > > > > > > > > > wouldn't have to really change the protocol at all to add > support. > > > > > > But > > > > > > > > > we'd have to change a lot of serialization code. Given > almost all > > > > > of > > > > > > > > > our use-cases for optional fields are adding an extra > field here or > > > > > > > > > there, it seems reasonable not to support it for right now. > > > > > > > > > > > > > > > > > > best, > > > > > > > > > Colin > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > -Jose > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
