The APIs in the current KIP look good to me. Just a couple questions: why
does filter not return Headers? Also would it be useful if the key is a
regex?
On the point of immutability.. One option might be to use a mutable object
only when passing the headers through the interceptor chain. I think as
long as we resort to mutability only when clear performance results show
that it is worthwhile, I am satisfied. As Ismael noted, for common
scenarios it is possible to get reasonable performance with immutable
objects.
-Jason
On Fri, Feb 24, 2017 at 8:48 AM, Michael Pearce <michael.pea...@ig.com>
wrote:
> Hi
>
> On 1, How can you guarantee two separate implemented clients would add
> the headers in the same order we are not specifying an order at the
> protocol level (nor should we) with regards to keyA being ordered before
> keyB? We shouldn’t be expecting keyA to be always set before keyB.
>
> On 2, I believe we have changed the naming based on feedback from Jason
> already, e.g. we don’t have “get” method that inferred O(1) performance,
> like wise nor “put” but we have an “append”
>
> On 3, in the KafkaProducer, I think we have mutability already, the value
> for time is changed if it is null, at the point of send:
> “
> long timestamp = record.timestamp() == null ?
> time.milliseconds() : record.timestamp();
> “
>
> As such the timestamp is already mutable, so what’s the difference here,
> we already have some mixed semantics. On timestamp.
> e.g. currently if I send to records with timestamp not set, the wire
> binary sent the value for the timestamp would be different, as such we have
> mutation for the same record.
>
> On 4, I think we should not expect not 1 or 2 headers, but infact 10’s of
> headers. This is the concern on immutable headers, whilst the append
> self-reference works nicely, what if someone needs to remove a header?
>
> Trying to get this moving:
>
> If we really wanted Immutable Headers and essentially you guys wont give
> +1 for it without.
>
> Whats the feeling for adding methods to ProducerRecord that does the
> boiler plate code or creating a new ProducerRecord with the altered new
> headers (appended or removed) inside. E.g.
>
> ProducerRecord {
>
>
> ProducerRecord append(Iterable<Headers> headersToAppend){
> return new ProducerRecord(key, value, headers.append(headersToAppend),
> ….)
> }
>
> ProducerRecord remove(Iterable<Headers> headersToAppend){
> return new ProducerRecord(key, value, headers.remove(headersToAppend),
> ….)
> }
>
> }
>
> Were the headers methods actually returns new objects, and the producer
> records methods create a new producer record with all the current values,
> but with the new modified headers.
>
> Then interceptors / code return this new object?
>
>
> Cheers
> Mike
>
>
>
>
>
>
> On 24/02/2017, 16:02, "isma...@gmail.com on behalf of Ismael Juma" <
> isma...@gmail.com on behalf of ism...@juma.me.uk> wrote:
>
> Hi Michael,
>
> Did you mean that you were happy to compromise to keep it mutable or
> immutable? You wrote the former, but it sounded from the sentence that
> it
> could have been a typo. So, my thoughts on this is that there are a few
> things to take into account:
>
> 1. Semantics
> 2. Simplicity of use (the common operations should be easy to do)
> 3. If it's easy to reason about and safe (immutability helps with this)
> 4. Efficiency (both memory and CPU usage)
>
> Regarding 1, I think it would be good to be very clear about the
> guarantees
> that we are providing. It seems that we are saying that keys are
> unordered,
> but what about the case where there are multiple values for the same
> key?
> It seems that for some use cases (e.g. lineage), it may be useful to
> add
> values to the same key while preserving the order.
>
> Regarding 2, I agree that it's useful to have methods in `Headers` for
> the
> very common use cases although we have to be careful with the naming to
> avoid giving the wrong impression. Also, when it comes to `Map.Entry`,
> I
> think I'd prefer a `toMap` method that simply gives the user a Map if
> that's what they want (it makes it clear that there's a conversion
> happening).
>
> Regarding 3, the concern I have if we make the headers mutable is that
> it
> seems to introduce some inconsistencies and potential edge cases. At
> the
> moment, it's safe to keep a ProducerRecord and resend it, for example.
> If
> the record is mutated by an interceptor, then this can lead to weird
> behaviour. Also, it seems inconsistent that one has to create a new
> ProducerRecord to modify the record timestamp, but that one has to
> mutate
> the record to add headers. It seems like one should either embrace
> immutability or mutability, but mixing both is not ideal.
>
> Regarding 4, for the cases where there are a small number of headers
> and/or
> 1 or 2 interceptors, it doesn't seem difficult to come up with
> reasonable
> implementations for mutable and immutable cases that do a good enough
> job.
> However, if the number of headers and interceptors is large, then care
> is
> needed for the immutable case to avoid unnecessary copying. A simple
> option
> that adds little memory overhead if we have Header instances is to
> simply
> add a self-reference to the previous Header in the linked list.
>
> Ismael
>
> On Thu, Feb 23, 2017 at 1:09 AM, Michael Pearce <michael.pea...@ig.com
> >
> wrote:
>
> > Im happy to compromise to keep it mutable but move to an append
> style api.
> > (as in guava interables concat)
> >
> > class Headers {
> > Headers append(Iterable<Header> headers);
> > }
> >
> >
> > I don’t think we’d want prepend, this would give the idea of
> guaranteed
> > ordering, when in actual fact we don’t provide that guarantee (.e.g
> one
> > client can put headerA, then headerB, but another could put headerB
> then
> > headerA, this shouldn’t cause issues), Also what if we changed to a
> hashmap
> > for the internal implementation, its just a bucket of entries no
> ordering.
> > I think we just need to provide an api to add/append headers.
> >
> > This ok? If so ill update KIP to record this.
> >
> > Cheers
> > Mike
> >
> > On 23/02/2017, 00:37, "Jason Gustafson" <ja...@confluent.io> wrote:
> >
> > The point about usability is fair. It's also reasonable to
> expect that
> > common use cases such as appending headers should be done
> efficiently.
> >
> > Perhaps we could compromise with something like this?
> >
> > class Headers {
> > Headers append(Iterable<Header> headers);
> > Headers prepend(Iterable<Header> headers);
> > }
> >
> > That retains ease of use while still giving ourselves some
> flexibility
> > in
> > the implementation.
> >
> > -Jason
> >
> >
> > On Wed, Feb 22, 2017 at 3:03 PM, Michael Pearce <
> michael.pea...@ig.com
> > >
> > wrote:
> >
> > > I wasn’t referring to the headers needing to be copied, im
> meaning
> > the
> > > fact we’d be forcing a new producer record to be created, with
> all
> > the
> > > contents copied.
> > >
> > > i.e what will happen is utility method will be created or end
> up
> > being
> > > used, which does this, and returns the new ProducerRecord
> instance.
> > >
> > > ProducerRecord addHeader(ProducerRecord record, Header
> header){
> > > Return New ProducerRecord(record.key, record.value,
> > record.timestamp…..,
> > > record.headers.concat(header))
> > > }
> > >
> > > To me this seems ugly, but will be inevitable if we don’t make
> adding
> > > headers to existing records a simple clean method call.
> > >
> > >
> > >
> > > On 22/02/2017, 22:57, "Michael Pearce" <michael.pea...@ig.com>
> > wrote:
> > >
> > > Lazy init can achieve/avoid that.
> > >
> > > Re the concat, why don’t we implement that inside the
> Headers
> > rather
> > > than causing everyone to implement this as adding headers in
> > interceptors
> > > will be a dominant use case. We want a user friendly API.
> Having as
> > a user
> > > having to code this instead of having the headers handle this
> for me
> > seems
> > > redundant.
> > >
> > > On 22/02/2017, 22:34, "Jason Gustafson" <
> ja...@confluent.io>
> > wrote:
> > >
> > > 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
> > > > > > >
> > > > > > >
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> > > > > 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.
> > > >
> > >
> > >
> > >
> > >
> > > 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.
> > >
> >
> >
> > 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.
> >
>
>
> 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.
>
