On Tue, Aug 13, 2019, at 11:19, David Jacot 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.
Hi David, Thanks for the review. I changed this to be two separate unsigned varints, as you and Jason suggested. The extra complexity is just probably not worth it to save a byte here. Using two varints also saves space if the length of the tag and the length of the size are not similar in size (i.e. it improves the worst case scenario). > > 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). Yeah, I think this is a great idea. I added a section about updating to a new version of the request header and response header for message versions in flexibleVersions. This will give us the ability to add optional stuff to the headers when needed in the future. For things that span all requests, like ClientType, TraceId, etc., this will be very useful. best, Colin > > 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 > > > > > > > > > > > > > > > > > > > > > > > > > > > >
