Mailing-List: contact dev-help@kafka.apache.org; run by ezmlm
Precedence: bulk
Reply-To: dev@kafka.apache.org
MIME-Version: 1.0
In-Reply-To: <CAA9QSJLdvnKJgvkGjmss2Vwm5RNZD-FirjK6idN-MLhB8yZ5UQ@mail.gmail.com>
References: <AA0D3563-37DB-4821-9280-1B53DEE1C6CB@ig.com> <CAA9QSJJoTvHcx+7pVH1742HF75VGcfW748JhLmGou2FjJE1bjg@mail.gmail.com>
 <87f1063ce0ef460090596e94690b06c2@BMPRDEXC142.IGI.IG.LOCAL>
 <CAE1jLMPWX1FuM2xDE9hWgW9V7OtMtVhD=S6e8wuy4H7p2wvRWg@mail.gmail.com>
 <3427DE88-0CA4-4307-BD52-D9078E99A9CF@me.com> <CAE1jLMOZtFgF4yC9unzges_1qu=YfiW3-RF7=1RBAcSGkom4fg@mail.gmail.com>
 <60A37B8E-F8E8-49EE-90A8-E7B5F6C7E012@ig.com> <fca6780b0b30425cab043e232d165107@BMPRDEXC142.IGI.IG.LOCAL>
 <65539CBD-888D-4360-AF3C-AB05079F7196@me.com> <CALYgK0Gqq8mjNGX_d4=eXEmCWiZ5XU7qJPmSMtQWa5GaOJyVzg@mail.gmail.com>
 <8F2867A7-D8E9-4256-B7D1-D46B91188C84@me.com> <CALYgK0G=K8P1bHQXUOEkrcnFLE97WaKgjMWt_6k=X0V864NEcw@mail.gmail.com>
 <CALYgK0FRhVzfuGqLHXyB+d=xus9HpC+fAhgep7_E79W3qkissA@mail.gmail.com>
 <CALYgK0E1_ojs0ZRwEQpoWy76+K7qpJjrOFDabATRqWj9C8Nfow@mail.gmail.com>
 <CALYgK0E2xbJcN_di2tShg5RB8czr0P9=ut5=T237TiFPiBs3Ng@mail.gmail.com> <CAA9QSJLdvnKJgvkGjmss2Vwm5RNZD-FirjK6idN-MLhB8yZ5UQ@mail.gmail.com>
From: Ewen Cheslack-Postava <ewen@confluent.io>
Date: Tue, 2 Jan 2018 13:44:01 -0800
Message-ID: <CAE1jLMO0icz2y5mC=Le-8urAt-MPDm1Q1strxWPupLc5MVEoAA@mail.gmail.com>
Subject: Re: [DISCUSS] KIP 145 - Expose Record Headers in Kafka Connect
To: dev@kafka.apache.org
Content-Type: multipart/alternative; boundary="001a113f929c48619e0561d1ffba"
archived-at: Tue, 02 Jan 2018 21:44:21 -0000

--001a113f929c48619e0561d1ffba
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

A few thoughts, mostly just details:

* Is the SchemaAndValue return type from Headers necessary? We needed to
use that in Converters, but otherwise I believe no public API has to use
that type. If possible I think it is better to avoid making Connector
developers aware of that type.
* For SimpleHeaderConverter, if we encounter a bare byte array (i.e. not
within some other structure), should it just get written directly similar
to how strings are handled? I guess the problem with this is that you then
either don't know how to decode or might get a different type (e.g. if the
bytes were utf-8 compatible, they'd parse as a string). But I'm not sure
many people will expect the current format.
* Also, did you mean utf-8 there or something like base64? utf-8 might not
handle all byte arrays.
* Header.with and Header.rename don't seem like they're going to be
particularly useful or common, what's the expected use case for these?
We're getting a lot of new API surface area here, so I think it'd be good
to try to keep it to the necessities and most valuable extras.
* Header.valueAsType seems like it doesn't need to be exposed publicly
* How much of the conversion stuff should be in the Header class vs as
generic utilities available in another class. Having them in the Header API
makes it obvious they are available and headers seem like they may be the
most common use case. But none of that functionality is really specific to
headers and seems like it could be useful in writing connectors that
robustly handle different formats (e.g. keys might be a good example of
something you want to preserve, but a connector could easily encounter int,
long, and string keys under very common circumstances).
* In the Headers class, why deviate from the naming used in the core
Headers class? Specifically, at least allWithName and lastWithName are
different.
* Headers.apply - this seems like a departure from other APIs that don't
have map-like functionality. Is the reason for this to avoid allocating a
new Headers object or do you get a new one out? I think we need to take
care when doing this since if we mutate the existing Headers object, then
connectors that may allocate a single Headers object and use it repeatedly
would see it changing out from under them (and something like
prefixing/suffixing a header as part of a transform could result in it
being done repeatedly). If it allocates a new Headers object anyway, I'm
not sure I see that much value in the method.
* HeaderTo - I think you need to update the remove.headers config to be
operation
* AddHeader has some inconsistent InsertHeader terminology. InsertHeader is
more consistent with the existing InsertField, but either one works.
Alternatively, the naming isn't great but you could also structure adding a
header as an InsertField$Header transformation.
* We have ReplaceField for changing or dropping fields. Would the same
approach/naming make sense instead of DropHeader?

In general I think this is the right direction for making headers work both
flexibly but also easily in the default case.

-Ewen


On Tue, Jan 2, 2018 at 8:42 AM, Gwen Shapira <gwen@confluent.io> wrote:

> I got the impression that use of Strings in headers is really common, so
> the SimpleHeaderConverter makes a lot of sense to me. Agree that this
> introduces overhead, but perhaps simply documenting an easy "optimization=
"
> will be enough to help those who are concerned about it? Since the
> connector-devs decide whether they'll use the header data or not, they ca=
n
> override the converter as needed.
>
> Gwen
>
>
> On Tue, Jan 2, 2018 at 3:52 PM Randall Hauch <rhauch@gmail.com> wrote:
>
> > There's been a bit of discussion on the PR about the choice of the
> default
> > header converter. The proposal currently uses the new
> > `SimpleHeaderConverter` so that by default connector devs and users get
> > meaningful header values by default without much work. An alternative i=
s
> to
> > default to `ByteArrayConverter` so that by default the framework doesn'=
t
> > have to do much effort if headers aren't used/needed.
> >
> > Thoughts?
> >
> > On Tue, Dec 26, 2017 at 11:47 AM, Randall Hauch <rhauch@gmail.com>
> wrote:
> >
> > > Does anyone have any thoughts about this proposal for Connect header
> > > support?
> > >
> > > On Thu, Dec 21, 2017 at 4:14 PM, Randall Hauch <rhauch@gmail.com>
> wrote:
> > >
> > >> All,
> > >>
> > >> I've updated KIP-145 to reflect my proposal. The proposal addresses
> SMTs
> > >> and a different HeaderConverter default, but I'll be updating my PR =
(
> > >> https://github.com/apache/kafka/pull/4319) soon. Feedback is very
> > >> welcome!
> > >>
> > >> Best regards,
> > >>
> > >> Randall
> > >>
> > >> On Thu, Dec 14, 2017 at 10:20 AM, Randall Hauch <rhauch@gmail.com>
> > wrote:
> > >>
> > >>> Hi, Michael. Yeah, I liked your PR a lot, and there definitely are =
a
> > lot
> > >>> of similarities. But here are the more significant differences from
> my
> > >>> perspective (none of which are really that big):
> > >>>
> > >>> First, your `SubjectConverter` and my `HeaderConverter` are pretty
> > >>> similar -- mine is just more closely tied to headers. Also, we used
> > >>> slightly different approaches to dealing with the fact that the
> > `Converter`
> > >>> interface does not extend `Configurable`, which Connect now uses fo=
r
> > >>> transforms, connectors, etc. And our implementations take very
> > different
> > >>> approaches (see below).
> > >>>
> > >>> Second, I tried to follow Kafka client's `Header` and `Headers`
> > >>> interfaces (at least in concept) so that ConnectRecord has a
> `Headers`
> > >>> rather than a list of headers. It's a minor distinction, but I do
> think
> > >>> it's important for future-proofing to have an interface for the
> > collection
> > >>> to abstract and encapsulate logic/behavior as well as leaving room
> for
> > >>> alternative implementations. It also a convenient place to add
> methods
> > for
> > >>> source connectors and SMTs to easily add/modify/remove/transform
> > headers.
> > >>>
> > >>> Third, our "header converter" implementations are where most of the
> > >>> differences lie. Again, this goes back to my assertion that we shou=
ld
> > make
> > >>> the serdes and cast/conversion orthogonal. If we allow sink
> connectors
> > and
> > >>> SMTs to get header values in the type they want (e.g.,
> > >>> `Header.valueAsFloat()`), then we can tolerate a bit more variation
> in
> > how
> > >>> the header values are serialized and deserialized, since the serdes
> > >>> mechanism doesn't have to get the type exactly right for the sink
> > connector
> > >>> and SMT. My `SimpleHeaderConverter` serializes all of the types to
> > strings,
> > >>> but during deserialization it attempts to infer the schemas (easy f=
or
> > >>> primitive values, a bit harder for structured types). IIUC, neither
> > your
> > >>> approach or mine is really able to maintain Struct schemas, but IMO
> we
> > can
> > >>> add that over time with improved/different header converters if
> people
> > >>> really need it.
> > >>>
> > >>> Fourth, we use different defaults for the serdes implementation. I
> > >>> dislike the StringConverter because it converts everything to strin=
gs
> > that
> > >>> are then difficult to convert back to the original form, especially
> > for the
> > >>> structured types. This is why I created the `SimpleHeaderConverter`
> > >>> implementation, which doesn't need explicit configuration or explic=
it
> > >>> mapping of header names to types, and thus can be used as the
> default.
> > >>>
> > >>> Finally, while I hope that `SimpleHeaderConverter` and its schema
> > >>> inference will work most of the time with no special configuration,
> > >>> especially since the `Header` interface makes it easy to cast/conve=
rt
> > in
> > >>> sink connectors and SMTs, I do like how your
> > `PrimativeSubjectConverter`
> > >>> allows the user to manually control how the values are serialized. =
I
> > >>> thought of doing something similar, but I think that can be done at=
 a
> > later
> > >>> time if/when needed.
> > >>>
> > >>> I hope that makes sense.
> > >>>
> > >>> Randall
> > >>>
> > >>> On Tue, Dec 12, 2017 at 11:35 PM, Michael Andr=C3=A9 Pearce <
> > >>> michael.andre.pearce@me.com> wrote:
> > >>>
> > >>>> Hi Randall
> > >>>>
> > >>>> What=E2=80=99s the main difference between this and my earlier alt=
ernative
> > >>>> option PR
> > >>>> https://github.com/apache/kafka/pull/2942/files
> > >>>>
> > >>>> If none then +1.
> > >>>> From what I can tell the only difference I make is the headers you
> > >>>> support being able to cross convert primitive types eg if value
> after
> > >>>> conversion is integer you can still ask for float and it will type
> > concert
> > >>>> if possible.
> > >>>>
> > >>>> Cheers
> > >>>> Mike
> > >>>>
> > >>>>
> > >>>> Sent from my iPhone
> > >>>>
> > >>>> > On 13 Dec 2017, at 01:36, Randall Hauch <rhauch@gmail.com> wrote=
:
> > >>>> >
> > >>>> > Trying to revive this after several months of inactivity....
> > >>>> >
> > >>>> > I've spent quite a bit of time evaluating the current KIP-145
> > >>>> proposal and
> > >>>> > several of the suggested PRs. The original KIP-145 proposal is
> > >>>> relatively
> > >>>> > minimalist (which is very nice), and it adopts Kafka's approach =
to
> > >>>> headers
> > >>>> > where header keys are strings and header values are byte arrays.
> > IMO,
> > >>>> this
> > >>>> > places too much responsibility on the connector developers to kn=
ow
> > >>>> how to
> > >>>> > serialize and deserialize, which means that it's going to be
> > >>>> difficult to
> > >>>> > assemble into pipelines connectors and stream processors that ma=
ke
> > >>>> > different, incompatible assumptions. It also makes Connect heade=
rs
> > >>>> very
> > >>>> > different than Connect's keys and values, which are generally
> > >>>> structured
> > >>>> > and describable with Connect schemas. I think we need Connect
> > headers
> > >>>> to do
> > >>>> > more.
> > >>>> >
> > >>>> > The other proposals attempt to do more, but even my first propos=
al
> > >>>> doesn't
> > >>>> > seem to really provide a solution that works for Connect users a=
nd
> > >>>> > connector developers. After looking at this feature from a varie=
ty
> > of
> > >>>> > perspectives over several months, I now assert that Connect must
> > >>>> solve two
> > >>>> > orthogonal problems:
> > >>>> >
> > >>>> > 1) Serialization: How different data types are (de)serialized as
> > >>>> header
> > >>>> > values
> > >>>> > 2) Conversion: How values of one data type are converted to valu=
es
> > of
> > >>>> > another data type
> > >>>> >
> > >>>> > For the serialization problem, Ewen suggested quite a while back
> > that
> > >>>> we
> > >>>> > use something akin to `Converter` for header values. Unfortunate=
ly
> > we
> > >>>> can't
> > >>>> > directly reuse `Converters` since the method signatures don't
> allow
> > >>>> us to
> > >>>> > supply the header name and the topic name, but we could define a
> > >>>> > `HeaderConverter` that is similar to and compatible with
> `Converter`
> > >>>> such
> > >>>> > that a single class could implement both. This would align
> Connector
> > >>>> > headers with how message keys and values are handled. Each
> connector
> > >>>> could
> > >>>> > define which converter it wants to use; for backward compatibili=
ty
> > >>>> purposes
> > >>>> > we use a header converter by default that serialize values to
> > >>>> strings. If
> > >>>> > you want something other than this default, you'd have to specif=
y
> > the
> > >>>> > header converter options as part of the connector configuration;
> > this
> > >>>> > proposal changes the `StringConverter`, `ByteArrayConverter`, an=
d
> > >>>> > `JsonConverter` to all implement `HeaderConverter`, so these are
> all
> > >>>> > options. This approach supposes that a connector will serialize
> all
> > >>>> of its
> > >>>> > headers in the same way -- with string-like representations by
> > >>>> default. I
> > >>>> > think this is a safe assumption for the short term, and if we ne=
ed
> > >>>> more
> > >>>> > control to (de)serialize named headers differently for the same
> > >>>> connector,
> > >>>> > we can always implement a different `HeaderConverter` that gives
> > >>>> users more
> > >>>> > control.
> > >>>> >
> > >>>> > So that would solve the serialization problem. How about
> connectors
> > >>>> and
> > >>>> > transforms that are implemented to expect a certain type of head=
er
> > >>>> value,
> > >>>> > such as an integer or boolean or timestamp? We could solve this
> > >>>> problem
> > >>>> > (for the most part) by adding methods to the `Header` interface =
to
> > >>>> get the
> > >>>> > value in the desired type, and to support all of the sensible
> > >>>> conversions
> > >>>> > between Connect's primitives and logical types. So, a connector =
or
> > >>>> > transform could always call `header.valueAsObject()` to get the
> raw
> > >>>> > representation from the converter, but a connector or transform
> > could
> > >>>> also
> > >>>> > get the string representation by calling `header.valueAsString()=
`,
> > or
> > >>>> the
> > >>>> > INT64 representation by calling `header.valueAsLong()`, etc. We
> > could
> > >>>> even
> > >>>> > have converting methods for the built-in logical types (e.g.,
> > >>>> > `header.valueAsTimestamp()` to return a java.util.Date value tha=
t
> is
> > >>>> > described by Connect's Timestamp logical type). We can convert
> > >>>> between most
> > >>>> > primitive and logical types (e.g., anything to a STRING, INT32 t=
o
> > >>>> FLOAT32,
> > >>>> > etc.), but there are a few that don't make sense (e.g., ARRAY to
> > >>>> FLOAT32,
> > >>>> > INT32 to STRUCT, BYTE_ARRAY to anything, etc.), so these can
> throw a
> > >>>> > `DataException`.
> > >>>> >
> > >>>> > I've refined this approach over the last few months, and have a =
PR
> > >>>> for a
> > >>>> > complete prototype that demonstrates these concepts and
> techniques:
> > >>>> > https://github.com/apache/kafka/pull/4319
> > >>>> >
> > >>>> > This PR does *not* update the documentation, though I can add th=
at
> > if
> > >>>> we
> > >>>> > approve of this approach. And, we probably want to define (at
> least
> > >>>> on the
> > >>>> > KIP) some relatively obvious SMTs for copying header values into
> > >>>> record
> > >>>> > key/value fields, and extracting record key/value fields into
> header
> > >>>> values.
> > >>>> >
> > >>>> > @Michael, would you mind if I edited KIP-145 to reflect this
> > >>>> proposal? I
> > >>>> > would be happy to keep the existing proposal at the end of the
> > >>>> document (or
> > >>>> > remove it if you prefer, since it's already in the page history)=
,
> > and
> > >>>> we
> > >>>> > can revise as we choose a direction.
> > >>>> >
> > >>>> > Comments? Thoughts?
> > >>>> >
> > >>>> > Best regards,
> > >>>> >
> > >>>> > Randall
> > >>>> >
> > >>>> >
> > >>>> > On Thu, Oct 19, 2017 at 2:10 PM, Michael Andr=C3=A9 Pearce <
> > >>>> > michael.andre.pearce@me.com> wrote:
> > >>>> >
> > >>>> >> @rhauch
> > >>>> >>
> > >>>> >> Here is the previous discussion thread, just reigniting so we c=
an
> > >>>> discuss
> > >>>> >> against the original kip thread
> > >>>> >>
> > >>>> >>
> > >>>> >> Cheers
> > >>>> >>
> > >>>> >> Mike
> > >>>> >>
> > >>>> >> Sent from my iPhone
> > >>>> >>
> > >>>> >>> On 5 May 2017, at 02:21, Michael Pearce <Michael.Pearce@ig.com=
>
> > >>>> wrote:
> > >>>> >>>
> > >>>> >>> Hi Ewen,
> > >>>> >>>
> > >>>> >>> Did you get a chance to look at the updated sample showing the
> > idea?
> > >>>> >>>
> > >>>> >>> Did it help?
> > >>>> >>>
> > >>>> >>> Cheers
> > >>>> >>> Mike
> > >>>> >>>
> > >>>> >>> Sent using OWA for iPhone
> > >>>> >>> ________________________________________
> > >>>> >>> From: Michael Pearce <Michael.Pearce@ig.com>
> > >>>> >>> Sent: Wednesday, May 3, 2017 10:11:55 AM
> > >>>> >>> To: dev@kafka.apache.org
> > >>>> >>> Subject: Re: [DISCUSS] KIP 145 - Expose Record Headers in Kafk=
a
> > >>>> Connect
> > >>>> >>>
> > >>>> >>> Hi Ewen,
> > >>>> >>>
> > >>>> >>> As code I think helps, as I don=E2=80=99t think I explained wh=
at I meant
> > >>>> very
> > >>>> >> well.
> > >>>> >>>
> > >>>> >>> I have pushed what I was thinking to the branch/pr.
> > >>>> >>> https://github.com/apache/kafka/pull/2942
> > >>>> >>>
> > >>>> >>> The key bits added on top here are:
> > >>>> >>> new ConnectHeader that holds the header key (as string) and th=
en
> > >>>> header
> > >>>> >> value object header value schema
> > >>>> >>>
> > >>>> >>> new SubjectConverter which allows exposing a subject, in this
> case
> > >>>> the
> > >>>> >> subject is the key. - this can be used to register the header
> type
> > >>>> in repos
> > >>>> >> like schema registry, or in my case below in a property file.
> > >>>> >>>
> > >>>> >>>
> > >>>> >>> We can default the subject converter to String based of Byte
> based
> > >>>> where
> > >>>> >> all header values are treated safely as String or byte[] type.
> > >>>> >>>
> > >>>> >>> But this way you could add in your own converter which could b=
e
> > more
> > >>>> >> sophisticated and convert the header based on the key.
> > >>>> >>>
> > >>>> >>> The main part is to have access to the key, so you can look up
> the
> > >>>> >> header value type, based on the key from somewhere, aka a
> > properties
> > >>>> file,
> > >>>> >> or some central repo (aka schema repo), where the repo subject
> > could
> > >>>> be the
> > >>>> >> topic + key, or just key if key type is global, and the schema
> > could
> > >>>> be
> > >>>> >> primitive, String, byte[] or even can be more elaborate.
> > >>>> >>>
> > >>>> >>> Cheers
> > >>>> >>> Mike
> > >>>> >>>
> > >>>> >>> On 03/05/2017, 06:00, "Ewen Cheslack-Postava" <
> ewen@confluent.io>
> > >>>> wrote:
> > >>>> >>>
> > >>>> >>>   Michael,
> > >>>> >>>
> > >>>> >>>   Aren't JMS headers an example where the variety is a problem=
?
> > >>>> Unless
> > >>>> >> I'm
> > >>>> >>>   misunderstanding, there's not even a fixed serialization
> format
> > >>>> >> expected
> > >>>> >>>   for them since JMS defines the runtime types, not the wire
> > >>>> format. For
> > >>>> >>>   example, we have JMSCorrelationID (String), JMSExpires (Long=
),
> > and
> > >>>> >>>   JMSReplyTo (Destination). These are simply run time types, s=
o
> > we'd
> > >>>> >> need
> > >>>> >>>   either (a) a different serializer/deserializer for each or
> (b) a
> > >>>> >>>   serializer/deserializer that can handle all of them (e.g.
> Avro,
> > >>>> JSON,
> > >>>> >> etc).
> > >>>> >>>
> > >>>> >>>   What is the actual serialized format of the different fields=
?
> > And
> > >>>> if
> > >>>> >> it's
> > >>>> >>>   not specified anywhere in the KIP, why should using the
> > well-known
> > >>>> >> type for
> > >>>> >>>   the header key (e.g. use StringSerializer, IntSerializer, et=
c)
> > be
> > >>>> >> better or
> > >>>> >>>   worse than using a general serialization format (e.g. Avro,
> > JSON)?
> > >>>> >> And if
> > >>>> >>>   the latter is the choice, how do you decide on the format?
> > >>>> >>>
> > >>>> >>>   -Ewen
> > >>>> >>>
> > >>>> >>>   On Tue, May 2, 2017 at 12:48 PM, Michael Andr=C3=A9 Pearce <
> > >>>> >>>   michael.andre.pearce@me.com> wrote:
> > >>>> >>>
> > >>>> >>>> Hi Ewan,
> > >>>> >>>>
> > >>>> >>>> So on the point of JMS the predefined/standardised JMS and JM=
SX
> > >>>> headers
> > >>>> >>>> have predefined types. So these can be serialised/deserialise=
d
> > >>>> >> accordingly.
> > >>>> >>>>
> > >>>> >>>> Custom jms headers agreed could be a bit more difficult but o=
n
> > the
> > >>>> 80/20
> > >>>> >>>> rule I would agree mostly they're string values and as anyhow
> you
> > >>>> can
> > >>>> >> hold
> > >>>> >>>> bytes as a string it wouldn't cause any issue, defaulting to
> > that.
> > >>>> >>>>
> > >>>> >>>> But I think easily we maybe able to do one better.
> > >>>> >>>>
> > >>>> >>>> Obviously can override the/config the headers converter but w=
e
> > can
> > >>>> >> supply
> > >>>> >>>> a default converter could take a config file with key to type
> > >>>> mapping?
> > >>>> >>>>
> > >>>> >>>> Allowing people to maybe define/declare a header key with the
> > >>>> expected
> > >>>> >>>> type in some property file? To support string, byte[] and
> > >>>> primitives?
> > >>>> >> And
> > >>>> >>>> undefined headers just either default to String or byte[]
> > >>>> >>>>
> > >>>> >>>> We could also pre define known headers like the jms ones
> > mentioned
> > >>>> >> above.
> > >>>> >>>>
> > >>>> >>>> E.g
> > >>>> >>>>
> > >>>> >>>> AwesomeHeader1=3Dboolean
> > >>>> >>>> AwesomeHeader2=3Dlong
> > >>>> >>>> JMSCorrelationId=3DString
> > >>>> >>>> JMSXGroupId=3DString
> > >>>> >>>>
> > >>>> >>>>
> > >>>> >>>> What you think?
> > >>>> >>>>
> > >>>> >>>>
> > >>>> >>>> Cheers
> > >>>> >>>> Mike
> > >>>> >>>>
> > >>>> >>>>
> > >>>> >>>>
> > >>>> >>>>
> > >>>> >>>>
> > >>>> >>>>
> > >>>> >>>> Sent from my iPhone
> > >>>> >>>>
> > >>>> >>>>> On 2 May 2017, at 18:45, Ewen Cheslack-Postava <
> > ewen@confluent.io
> > >>>> >
> > >>>> >>>> wrote:
> > >>>> >>>>>
> > >>>> >>>>> A couple of thoughts:
> > >>>> >>>>>
> > >>>> >>>>> First, agreed that we definitely want to expose header
> > >>>> functionality.
> > >>>> >>>> Thank
> > >>>> >>>>> you Mike for starting the conversation! Even if Connect
> doesn't
> > do
> > >>>> >>>> anything
> > >>>> >>>>> special with it, there's value in being able to access/set
> > >>>> headers.
> > >>>> >>>>>
> > >>>> >>>>> On motivation -- I think there are much broader use cases.
> When
> > >>>> >> thinking
> > >>>> >>>>> about exposing headers, I'd actually use Replicator as only =
a
> > >>>> minor
> > >>>> >>>>> supporting case. The reason is that it is a very uncommon ca=
se
> > >>>> where
> > >>>> >>>> there
> > >>>> >>>>> is zero impedance mismatch between the source and sink of th=
e
> > data
> > >>>> >> since
> > >>>> >>>>> they are both Kafka. This means you don't need to think much
> > >>>> about data
> > >>>> >>>>> formats/serialization. I think the JMS use case is a better
> > >>>> example
> > >>>> >> since
> > >>>> >>>>> JMS headers and Kafka headers don't quite match up. Here's a
> > >>>> quick list
> > >>>> >>>> of
> > >>>> >>>>> use cases I can think of off the top of my head:
> > >>>> >>>>>
> > >>>> >>>>> 1. Include headers from other systems that support them: JMS
> (or
> > >>>> really
> > >>>> >>>> any
> > >>>> >>>>> MQ), HTTP
> > >>>> >>>>> 2. Other connector-specific headers. For example, from JDBC
> > maybe
> > >>>> the
> > >>>> >>>> table
> > >>>> >>>>> the data comes from is a header; for a CDC connector you mig=
ht
> > >>>> include
> > >>>> >>>> the
> > >>>> >>>>> binlog offset as a header.
> > >>>> >>>>> 3. Interceptor/SMT-style use cases for annotating things lik=
e
> > >>>> >> provenance
> > >>>> >>>> of
> > >>>> >>>>> data:
> > >>>> >>>>> 3a. Generically w/ user-supplied data like data center, host=
,
> > app
> > >>>> ID,
> > >>>> >>>> etc.
> > >>>> >>>>> 3b. Kafka Connect framework level info, such as the
> > connector/task
> > >>>> >>>>> generating the data
> > >>>> >>>>>
> > >>>> >>>>> On deviation from Connect's model -- to be honest, the KIP-8=
2
> > also
> > >>>> >>>> deviates
> > >>>> >>>>> quite substantially from how Kafka handles data already, so =
we
> > may
> > >>>> >>>> struggle
> > >>>> >>>>> a bit to rectify the two. (In particular, headers specify so=
me
> > >>>> >> structure
> > >>>> >>>>> and enforce strings specifically for header keys, but then
> > >>>> require you
> > >>>> >> to
> > >>>> >>>>> do serialization of header values yourself...).
> > >>>> >>>>>
> > >>>> >>>>> I think the use cases I mentioned above may also need
> different
> > >>>> >>>> approaches
> > >>>> >>>>> to how the data in headers are handled. As Gwen mentions, if
> we
> > >>>> expose
> > >>>> >>>> the
> > >>>> >>>>> headers to Connectors, they need to have some idea of the
> format
> > >>>> and
> > >>>> >> the
> > >>>> >>>>> reason for byte[] values in KIP-82 is to leave that decision
> up
> > >>>> to the
> > >>>> >>>>> organization using them. But without knowing the format,
> > >>>> connectors
> > >>>> >> can't
> > >>>> >>>>> really do anything with them -- if a source connector assume=
s
> a
> > >>>> format,
> > >>>> >>>>> they may generate data incompatible with the format used by
> the
> > >>>> rest of
> > >>>> >>>> the
> > >>>> >>>>> organization. On the other hand, I have a feeling most peopl=
e
> > >>>> will just
> > >>>> >>>> use
> > >>>> >>>>> <String, String> headers, so allowing connectors to embed
> > >>>> arbitrarily
> > >>>> >>>>> complex data may not work out well in practice. Or maybe we
> > leave
> > >>>> it
> > >>>> >>>>> flexible, most people default to using StringConverter for t=
he
> > >>>> >> serializer
> > >>>> >>>>> and Connectors will end up defaulting to that just for
> > >>>> compatibility...
> > >>>> >>>>>
> > >>>> >>>>> I'm not sure I have a real proposal yet, but I do think
> > >>>> understanding
> > >>>> >> the
> > >>>> >>>>> impact of using a Converter for headers would be useful, and
> we
> > >>>> might
> > >>>> >>>> want
> > >>>> >>>>> to think about how this KIP would fit in with transformation=
s
> > (or
> > >>>> if
> > >>>> >> that
> > >>>> >>>>> is something that can be deferred, handled separately from t=
he
> > >>>> existing
> > >>>> >>>>> transformations, etc).
> > >>>> >>>>>
> > >>>> >>>>> -Ewen
> > >>>> >>>>>
> > >>>> >>>>> On Mon, May 1, 2017 at 11:52 AM, Michael Pearce <
> > >>>> Michael.Pearce@ig.com
> > >>>> >>>
> > >>>> >>>>> wrote:
> > >>>> >>>>>
> > >>>> >>>>>> Hi Gwen,
> > >>>> >>>>>>
> > >>>> >>>>>> Then intent here was to allow tools that perform similar ro=
le
> > to
> > >>>> >> mirror
> > >>>> >>>>>> makers of replicating the messaging from one cluster to
> > >>>> another.  Eg
> > >>>> >>>> like
> > >>>> >>>>>> mirror make should just be taking and transferring the
> headers
> > >>>> as is.
> > >>>> >>>>>>
> > >>>> >>>>>> We don't actually use this inside our company, so not
> exposing
> > >>>> this
> > >>>> >>>> isn't
> > >>>> >>>>>> an issue for us. Just believe there are companies like
> > confluent
> > >>>> who
> > >>>> >>>> have
> > >>>> >>>>>> tools like replicator that do.
> > >>>> >>>>>>
> > >>>> >>>>>> And as good citizens think we should complete the work and
> > >>>> expose the
> > >>>> >>>>>> headers same as in the record to at least allow them to
> > >>>> replicate the
> > >>>> >>>>>> messages as is. Note Steph seems to want it.
> > >>>> >>>>>>
> > >>>> >>>>>> Cheers
> > >>>> >>>>>> Mike
> > >>>> >>>>>>
> > >>>> >>>>>> Sent using OWA for iPhone
> > >>>> >>>>>> ________________________________________
> > >>>> >>>>>> From: Gwen Shapira <gwen@confluent.io>
> > >>>> >>>>>> Sent: Monday, May 1, 2017 2:36:34 PM
> > >>>> >>>>>> To: dev@kafka.apache.org
> > >>>> >>>>>> Subject: Re: [DISCUSS] KIP 145 - Expose Record Headers in
> Kafka
> > >>>> >> Connect
> > >>>> >>>>>>
> > >>>> >>>>>> Hi,
> > >>>> >>>>>>
> > >>>> >>>>>> I'm excited to see the community expanding Connect in this
> > >>>> direction!
> > >>>> >>>>>> Headers + Transforms =3D=3D Fun message routing.
> > >>>> >>>>>>
> > >>>> >>>>>> I like how clean the proposal is, but I'm concerned that it
> > kinda
> > >>>> >>>> deviates
> > >>>> >>>>>> from how Connect handles data elsewhere.
> > >>>> >>>>>> Unlike Kafka, Connect doesn't look at all data as
> byte-arrays,
> > >>>> we have
> > >>>> >>>>>> converters that take data in specific formats (JSON, Avro)
> and
> > >>>> turns
> > >>>> >> it
> > >>>> >>>>>> into Connect data types (defined in the data
> > <https://maps.google.com/?q=3Dct+data+types+(defined+in+the+
> data&entry=3Dgmail&source=3Dg>
> > api). I think it
> > >>>> will be
> > >>>> >>>> more
> > >>>> >>>>>> consistent for connector developers to also get headers as
> some
> > >>>> kind
> > >>>> >> of
> > >>>> >>>>>> structured or semi-structured data (and to expand the
> > converters
> > >>>> to
> > >>>> >>>> handle
> > >>>> >>>>>> header conversions as well).
> > >>>> >>>>>> This will allow for Connect's separation of concerns -
> > Connector
> > >>>> >>>> developers
> > >>>> >>>>>> don't worry about data formats (because they get the intern=
al
> > >>>> connect
> > >>>> >>>>>> objects) and Converters do all the data format work.
> > >>>> >>>>>>
> > >>>> >>>>>> Another thing, in my experience, APIs work better if they a=
re
> > >>>> put into
> > >>>> >>>> use
> > >>>> >>>>>> almost immediately - so difficulties in using the APIs are
> > >>>> immediately
> > >>>> >>>>>> surfaced. Are you planning any connectors that will use thi=
s
> > >>>> feature
> > >>>> >>>> (not
> > >>>> >>>>>> necessarily in Kafka, just in general)? Or perhaps we can
> think
> > >>>> of a
> > >>>> >>>> way to
> > >>>> >>>>>> expand Kafka's file connectors so they'll use hea
> > <https://maps.google.com/?q=3Dfile+connectors+so+they'll+
> use+hea&entry=3Dgmail&source=3Dg>ders
> > somehow
> > >>>> (can't
> > >>>> >>>> think
> > >>>> >>>>>> of anything, but maybe?).
> > >>>> >>>>>>
> > >>>> >>>>>> Gwen
> > >>>> >>>>>>
> > >>>> >>>>>> On Sat, Apr 29, 2017 at 12:12 AM, Michael Pearce <
> > >>>> >> Michael.Pearce@ig.com
> > >>>> >>>>>
> > >>>> >>>>>> wrote:
> > >>>> >>>>>>
> > >>>> >>>>>>> Hi All,
> > >>>> >>>>>>>
> > >>>> >>>>>>> Now KIP-82 is committed I would like to discuss extending
> the
> > >>>> work to
> > >>>> >>>>>>> expose it in Kafka Connect, its primary focus being so
> > >>>> connectors
> > >>>> >> that
> > >>>> >>>>>> may
> > >>>> >>>>>>> do similar tasks as MirrorMakers, either Kafka->Kafka or
> > >>>> JMS-Kafka
> > >>>> >>>> would
> > >>>> >>>>>> be
> > >>>> >>>>>>> able to replicate the headers.
> > >>>> >>>>>>> It would be ideal but not mandatory for this to go in 0.11
> > >>>> release so
> > >>>> >>>> is
> > >>>> >>>>>>> available on day one of headers being available.
> > >>>> >>>>>>>
> > >>>> >>>>>>> Please find the KIP here:
> > >>>> >>>>>>> https://cwiki.apache.org/confluence/display/KAFKA/KIP-
> > >>>> >>>>>>> 145+-+Expose+Record+Headers+in+Kafka+Connect
> > >>>> >>>>>>>
> > >>>> >>>>>>> Please find an initial implementation as a PR here:
> > >>>> >>>>>>> https://github.com/apache/kafka/pull/2942
> > >>>> >>>>>>>
> > >>>> >>>>>>> Kind Regards
> > >>>> >>>>>>> Mike
> > >>>> >>>>>>> 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 n=
ot
> > >>>> 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, compan=
y
> > >>>> 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.
> > >>>> >>>>>>>
> > >>>> >>>>>>
> > >>>> >>>>>>
> > >>>> >>>>>>
> > >>>> >>>>>> --
> > >>>> >>>>>> *Gwen Shapira*
> > >>>> >>>>>> Product Manager | Confluent
> > >>>> >>>>>> 650.450.2760 <(650)%20450-2760> <(650)%20450-2760> |
> @gwenshap
> > >>>> >>>>>> Follow us: Twitter <https://twitter.com/ConfluentInc> | blo=
g
> > >>>> >>>>>> <http://www.confluent.io/blog>
> > >>>> >>>>>> 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 send=
er
> > 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 no=
t
> > >>>> 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) a=
nd
> > 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 confidenti=
al
> > >>>> and for
> > >>>> >> the use of the addressee only, unless otherwise indicated. If y=
ou
> > >>>> are not
> > >>>> >> the intended recipient, please do not read, copy, use or disclo=
se
> > to
> > >>>> others
> > >>>> >> this message or any attachment. Please also notify the sender b=
y
> > >>>> replying
> > >>>> >> to this email or by telephone (+44(020 7896 0011) and then dele=
te
> > >>>> 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 neithe=
r
> > >>>> 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 I=
G
> > >>>> Index
> > >>>> >> Limited (a company registered in England and Wales, company
> number
> > >>>> >> 01190902). Registered address at Cannon Bridge House, 25 Dowgat=
e
> > >>>> Hill,
> > >>>> >> London EC4R 2YA. Both IG Markets Limited (register number 19535=
5)
> > >>>> and IG
> > >>>> >> Index Limited (register number 114059) are authorised and
> regulated
> > >>>> by the
> > >>>> >> Financial Conduct Authority.
> > >>>> >>
> > >>>>
> > >>>
> > >>>
> > >>
> > >
> >
>

--001a113f929c48619e0561d1ffba--