I thought the argument was against creating the extra objects unnecessarily (i.e. if they were not accessed). And note that making the Headers immutable doesn't necessarily mean that they need to be copied: you can do a trick like Guava's Iterables.concat to add additional headers without changing the underlying collections.
-Jason On Wed, Feb 22, 2017 at 2:22 PM, Michael Pearce <michael.pea...@ig.com> wrote: > If the argument for not having a map holding the key, value pairs is due > to garbage creation of HashMap entry's, forcing the creation of a whole new > producer record to simply add a head, surely is creating a-lot more? > ________________________________________ > From: Jason Gustafson <ja...@confluent.io> > Sent: Wednesday, February 22, 2017 10:09 PM > To: dev@kafka.apache.org > Subject: Re: [DISCUSS] KIP-82 - Add Record Headers > > The current producer interceptor API is this: > > ProducerRecord<K, V> onSend(ProducerRecord<K, V> record); > > So adding a header means creating a new ProducerRecord with a new header > added to the current headers and returning it. Would that not work? > > -Jason > > On Wed, Feb 22, 2017 at 1:45 PM, Michael Pearce <michael.pea...@ig.com> > wrote: > > > So how would you have this work if not mutable where interceptors would > > add headers? > > > > Sent using OWA for iPhone > > ________________________________________ > > From: Jason Gustafson <ja...@confluent.io> > > Sent: Wednesday, February 22, 2017 8:42:27 PM > > To: dev@kafka.apache.org > > Subject: Re: [DISCUSS] KIP-82 - Add Record Headers > > > > I think the point on the mutability of Headers is worth discussing a > little > > more. As far as I can tell, once the ProducerRecord (or ConsumerRecord) > is > > constructed, there should be no need to further change the headers. Is > that > > correct? If so, then why not enforce that that is the case through the > API? > > One problem with mutability it that it constrains the implementation of > > Headers. For example, if we were backing with a byte slice, would we > recopy > > the bytes if a header is added or would we maintain a satellite > collection > > of added records. Seems not great either way. If we really think > mutability > > is needed, perhaps we could add a method to headers to convert it to a > > mutable type (e.g. a Headers.toMap)? > > > > I'm also with Ismael about exposing Headers.get(). I thought it might > make > > sense to have a method like this instead: > > > > Iterable<Header> findMatching(Pattern pattern); > > > > This makes the (potential) need to scan the headers clear in the API. I'd > > also be fine exposing no getter at all. In general, Ï think it's good to > > start with a minimalistic API and work from there since it's always > easier > > to add methods than remove them. > > > > -Jason > > > > On Wed, Feb 22, 2017 at 9:16 AM, Michael Pearce <michael.pea...@ig.com> > > wrote: > > > > > > > > Hi Ismael > > > > > > On point 1, > > > > > > Sure makes sense will update shortly. > > > > > > On point 2, > > > > > > Setter/getter typical to properties/headers api’s traditionally are map > > > styled interfaces and what I believe is most expected styled thus the > > Key, > > > Value setter. > > > Also it would mean rather than an interface, we would be making our > > > internal header impl object we have for the array, exposed. E.g. if we > > had > > > a Map really this would be Map.Entry interface, this is the same > reasons > > on > > > the map interface I cannot actually make the underlying Node object > > that’s > > > the implementation for HashMap, so that internals can be changed. > > > > > > > > > On point 3, > > > > > > I think it people do expect it to be performant, thus why originally > > > concern I raised with using an array for to me is an early memory > > > optimisation. I think the user experience of properties/headers is on a > > > get/set model. This is why its important we have encapsulated logic > that > > > then allows us to change this to a map, if this becomes and issue, and > > the > > > memory overhead of hashmap is less so. > > > > > > > > > > > > > > > On 22/02/2017, 15:56, "isma...@gmail.com on behalf of Ismael Juma" < > > > isma...@gmail.com on behalf of ism...@juma.me.uk> wrote: > > > > > > Hi all, > > > > > > Great to see the progress that has been achieved on this one. :) A > > few > > > comments regarding the APIs (I'm still reviewing the message format > > > changes): > > > > > > 1. Nit: `getHeaders` in `ProducerRecord` and `ConsumerRecord` > should > > be > > > named `headers` (we avoid the `get` prefix in Kafka) > > > > > > 2. The `Headers` class is mutable (there's an `add` method). Does > it > > > need > > > to be? If so, it would be good to explain why. Related to that, we > > > should > > > also explain the thinking around thread-safety. If we keep the > `add` > > > method, it may make sense for it to take a `Header` (that way we > can > > > add > > > things to `Header` without changing the interface). > > > > > > 3. Do we need the `Headers.get()` method? People usually assume > that > > > `get` > > > would be efficient, but depending on the implementation (the > current > > > proposal states that an array would be used), it may not be. If we > > > expect > > > the number of headers to be small, it doesn't matter though. > > > > > > Ismael > > > > > > On Tue, Feb 21, 2017 at 6:38 PM, Michael Pearce < > > michael.pea...@ig.com > > > > > > > wrote: > > > > > > > Hi Jason, > > > > > > > > Have converted the interface/api bullets into interface code > > > snippets. > > > > > > > > Agreed implementation won’t take too long. We have early versions > > > already. > > > > Maybe a week before you think about merging I would assume it > would > > > be more > > > > stabilised? I was thinking then we could fork from your confluent > > > branch, > > > > making and then holding KIP-82 changes in a patch file, that we > can > > > then > > > > re-fork from apache once KIP98 final is merged, and apply patch > > with > > > last > > > > minute changes. > > > > > > > > Cheers > > > > Mike > > > > > > > > > > > > On 22/02/2017, 00:56, "Jason Gustafson" <ja...@confluent.io> > > wrote: > > > > > > > > Hey Michael, > > > > > > > > Awesome. I have a minor request. The APIs are currently > > > documented as a > > > > wiki list. Would you mind adding a code snippet instead? > It's a > > > bit > > > > easier > > > > to process. > > > > > > > > How will be best to manage this, as we will obviously build > off > > > your > > > > KIP’s > > > > > protocol changes, to avoid a merge hell, should we branch > > from > > > your > > > > branch > > > > > in the confluent repo or is it worth having a KIP-98 > special > > > branch > > > > in the > > > > > apache git, that we can branch/fork from? > > > > > > > > > > > > I was thinking about this also. Ideally we'd like to get the > > > changes > > > > in as > > > > close together as possible since we only want one magic bump > > and > > > some > > > > users > > > > deploy trunk. The level of effort to change the format for > > > headers > > > > seems > > > > not too high. Do you agree? My guess is that the KIP-98 > message > > > format > > > > patch will take 2-3 weeks to review before we merge to trunk, > > so > > > you > > > > could > > > > hold off implementing until that patch has somewhat > stabilized. > > > That > > > > would > > > > save some potential rebase pain. > > > > > > > > -Jason > > > > > > > > > > > > The information contained in this email is strictly confidential > > and > > > for > > > > the use of the addressee only, unless otherwise indicated. If you > > > are not > > > > the intended recipient, please do not read, copy, use or disclose > > to > > > others > > > > this message or any attachment. Please also notify the sender by > > > replying > > > > to this email or by telephone (+44(020 7896 0011) and then delete > > the > > > > email and any copies of it. Opinions, conclusion (etc) that do > not > > > relate > > > > to the official business of this company shall be understood as > > > neither > > > > given nor endorsed by it. 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Please also notify the sender by replying > > to this email or by telephone (+44(020 7896 0011) and then delete the > email > > and any copies of it. Opinions, conclusion (etc) that do not relate to > the > > official business of this company shall be understood as neither given > nor > > endorsed by it. IG is a trading name of IG Markets Limited (a company > > registered in England and Wales, company number 04008957) and IG Index > > Limited (a company registered in England and Wales, company number > > 01190902). Registered address at Cannon Bridge House, 25 Dowgate Hill, > > London EC4R 2YA. Both IG Markets Limited (register number 195355) and IG > > Index Limited (register number 114059) are authorised and regulated by > the > > Financial Conduct Authority. > > > The information contained in this email is strictly confidential and for > the use of the addressee only, unless otherwise indicated. If you are not > the intended recipient, please do not read, copy, use or disclose to others > this message or any attachment. Please also notify the sender by replying > to this email or by telephone (+44(020 7896 0011) and then delete the email > and any copies of it. Opinions, conclusion (etc) that do not relate to the > official business of this company shall be understood as neither given nor > endorsed by it. IG is a trading name of IG Markets Limited (a company > registered in England and Wales, company number 04008957) and IG Index > Limited (a company registered in England and Wales, company number > 01190902). Registered address at Cannon Bridge House, 25 Dowgate Hill, > London EC4R 2YA. Both IG Markets Limited (register number 195355) and IG > Index Limited (register number 114059) are authorised and regulated by the > Financial Conduct Authority. >
