Hi all,
This has certainly taken quite a turn! I wish we could get this done
without adding another pluggable interface but if the benefit is that now
any SMT--new or pre-existing--can be conditionally applied, it seems like
it might be worth it.
As far as the proposed design goes, some thoughts:
1. There isn't a clear reason why exceptions thrown from predicates should
be treated differently from exceptions thrown by transformations. We have
reasonable error-tolerance mechanisms in the Connect framework; why
silently swallow errors, especially if the risk is publishing potentially
corrupted data to Kafka or an external system because an SMT that should
have been applied wasn't?
2. It might be worth noting that the interface is a worker plugin, and that
presumably it would be loaded in the same way as other worker plugins such
as converters, connectors, and REST extensions. This would include aliasing
behavior that would allow users to specify predicates using their simple
class names as long as no two predicate plugins with the same simple name
were available on the worker.
3. Why would the Filter SMT explicitly take in a predicate in its
configuration if predicates can be applied to all SMTs? Just reading the
idea for a filter SMT, it seemed like the behavior would be that the SMT
would take in no configuration parameters and just blindly drop everything
that it sees, but typical use would involve pairing it with a predicate.
4. The question mark syntax seems a little cryptic, and combining the
configuration properties for the predicate and the transformation in the
same namespace ("transforms.<name>.*) seems a little noisy. What do you
think about allowing predicates to be configured in their own namespace,
and referenced by name in a single "predicate" (or maybe "?predicate" if we
really want to avoid risking backwards compatibility concerns) property?
This would also enable them to be more easily reused across several SMTs.
For example, you might configure a worker with these properties (assuming
plugin aliasing is supported for predicates in the same way that it is for
transformations):
transforms: t2
transforms.t2.predicate: has-my-prefix
transforms.t2.type:ExtractField$Key
transforms.t2.field: c1
predicates: has-my-prefix
predicates.has-my-prefix.type: TopicNameMatch
predicates.has-my-prefix.negate: true
predicates.has-my-prefix.pattern: my-prefix-.*
Excited to see how this is evolving and I think we're heading towards
something really useful for the Connect framework.
Cheers,
Chris
On Fri, May 1, 2020 at 9:51 AM Andrew Schofield <andrew_schofi...@live.com>
wrote:
> Hi Tom,
> Looks good to me.
>
> Thanks,
> Andrew
>
> On 01/05/2020, 16:24, "Tom Bentley" <tbent...@redhat.com> wrote:
>
> Hi,
>
> I've updated the KIP to reflect recent discussions. Please note the
> following:
>
> 1. I've described a HasHeaderKey predicate rather than HeaderKeyMatches
> because at the moment Headers doesn't expose the whole set of headers,
> only
> those with a specific name. Exposing this would significantly increase
> the
> scope of this KIP but relatively little extra benefit.
> 2. I used org.apache.kafka.connect.transformer.predicates rather than
> org.apache.kafka.connect.predicates, since I thought it better
> reflected
> the use of predicates within transforms. I'm flexible on this one if
> someone has a good case for the original name. For example the original
> package name would be more appropriate if we were expecting Connectors
> to
> make use of Predicates somehow.
> 3. I've dropped the special case of not needing to provide a FQN for
> predicate classes in that package, since this isn't something
> supported by
> transformations themselves as far as I know. I like the idea, but it
> seemed
> inconsistent to need it for transformations but not for predicates.
> 4. Chris, I've used your suggestions for a validate() method for the
> extra
> configurability needed. I've also added this to Predicate (even though
> I
> don't need it) for consistency with Connector and Transformation.
> 5. For negating the result of a predicate I decided it was clearer to
> just
> have a "negate" config parameter, supported by all predicates, than to
> reach for more punctuation.
>
> I'd be grateful for any more feedback people might have.
>
> Kind regards,
>
> Tom
>
> On Tue, Apr 28, 2020 at 3:50 PM Andrew Schofield <
> andrew_schofi...@live.com>
> wrote:
>
> > Hi Tom,
> > I think we should go for a consistent naming convention for the
> > predicates, maybe so they
> > read nicely if you say "IF" first. Here's a suggestion for
> predicates that
> > the KIP could introduce:
> > - TopicNameMatches
> > - HeaderKeyMatches
> > - RecordIsTombstone
> >
> > On naming, I also suggest using
> > org.apache.kafka.connect.predicates.Predicate
> > as the name for the interface.
> >
> > I hadn't settled on a preference for negation. I suppose there are
> three
> > results
> > from evaluating a predicate - true, false or an exception caught by
> Kafka
> > Connect.
> > I suggest the exception case is always a predicate fail so the
> guarded
> > transformation
> > is skipped. Initially I'd preferred having the predicate be
> configured to
> > return a
> > negated result to give a "not match" behaviour. Thinking again now, I
> > prefer something like:
> >
> > transforms: t1
> > transforms.t1.?type: RecordIsTombstone
> > transforms.t1.type:
> org.apache.kafka.connect.transforms.InsertField$Value
> > transforms.t1.static.field: deleted
> > transforms.t1.static.value: true
> >
> > The "?" means the transform guarded by the predicate runs in the
> Predicate
> > returns true.
> >
> > transforms: t2
> > transforms.t2.?!type:
> org.apache.kafka.connect.predicates.TopicNameMatch
> > transforms.t2.?regex: my-prefix-.*
> > transforms.t2.type:
> org.apache.kafka.connect.transforms.ExtractField$Key
> > transforms.t2.field: c1
> >
> > The "?!" means the transform guarded by the predicate runs if the
> Predicate
> > returns false.
> >
> > I think adding a Filter SMT that uses a Predicate is a nice idea.
> >
> > Cheers,
> > Andrew
> >
> > On 28/04/2020, 09:44, "Tom Bentley" <tbent...@redhat.com> wrote:
> >
> > Hi Andrew and Chris,
> >
> > Firstly, thanks for the input.
> >
> > To me, the ?type syntax has some pros and cons. On the pros side:
> > * it's pretty succinct
> > * it's flexible enough for the use cases we've identified so far.
> >
> > On the cons side:
> > * it's a bit cryptic; I don't think people who didn't know it
> already
> > would
> > be able to guess what ?type meant.
> > * it doesn't work so well if there is a whole chain of
> transformations
> > which need to be applied conditionally (that can still be done,
> of
> > course,
> > but the user has to duplicate the configuration for each SMT).
> Nor
> > does it
> > work if you need something akin to a "nested if" (you could fake
> it
> > using
> > And), but we don't really expect people to need that.
> >
> > Andrew, you didn't give an example of a negated match. Would you
> use
> > something like !?type for that, or did you have another idea?
> >
> > On balance, I think this is a reasonable trade off.
> >
> > I agree that exposing RecordPredicate as a public API, while
> providing
> > common implementation(s) would allow most use cases to be covered
> > without
> > coding, but also allow people with specific unaddressed needs to
> > implement
> > their own without having to write a streaming application to do
> so.
> > Again,
> > I think this is a reasonable trade off.
> >
> > It would be helpful to have a consensus about exactly which
> condition
> > implementations the KIP should provide. I think we all agree that
> > TopicMatches (or should it be TopicNameMatches?) should be
> included.
> > HasHeader (or should it be HasHeaderWithName or
> HasHeaderMatching for a
> > regex version?), And and Or all seem like they could be useful,
> even
> > though
> > no one has pointed to concrete use cases. It might also be worth
> > considering that it would be natural to add a Filter SMT which
> filtered
> > records using a RecordPredicate. Perhaps that provides
> motivation for
> > conditions on the record key as well? If people think the Filter
> SMT
> > would
> > be useful I'm willing to include it in this KIP, since it seems
> > straightforward.
> >
> > If people are happy with this approach, I'll update the KIP.
> >
> > Kind regards,
> >
> > Tom
> >
> > On Sun, Apr 26, 2020 at 3:00 PM Andrew Schofield <
> > andrew_schofi...@live.com>
> > wrote:
> >
> > > Hi,
> > > I'm suggesting that RecordPredicate be another pluggable
> interface
> > that
> > > users
> > > could conceivably implement on their own, and that the KIP
> > introduces the
> > > most likely ones as supplied implementations, much as there
> are SMT
> > > implementations such as HoistField. I don't really see users
> > implementing
> > > their own RecordPredicate, but the supplied ones would
> probably have
> > a
> > > common
> > > interface and it seems a pity not to expose that as an
> external API.
> > >
> > > SMT is essentially a toolkit for Kafka Connect and I think
> > RecordPredicate
> > > would be a nice minor enhancement and I'd be happy to
> contribute
> > code.
> > >
> > > In order to make it simpler to configure, I suggest that the
> class
> > name
> > > configured
> > > using "?type" would be assumed to be in package
> > > org.apache.kafka.connect.predicates
> > > in the absence of a package name so that shorter names such as
> > > "TopicMatches"
> > > could be used.
> > >
> > > Cheers,
> > > Andrew Schofield
> > > IBM Event Streams
> > >
> > > On 25/04/2020, 21:22, "Christopher Egerton" <
> chr...@confluent.io>
> > wrote:
> > >
> > > Hi Andrew,
> > >
> > > I know a DSL seems like overkill, and I'm not attached to
> it by
> > any
> > > means,
> > > but I do think it serves a vital purpose in that it allows
> > people who
> > > don't
> > > know how or have the time to write Java code to act on
> data being
> > > processed
> > > by connectors.
> > >
> > > Are you proposing that the "RecordPredicate" be another
> pluggable
> > > interface
> > > that users could then implement on their own? Or, would
> this be
> > purely
> > > a
> > > syntactic expansion to SMT configuration with some subset
> of
> > hard-coded
> > > predicates provided by the framework? I think there's
> value in
> > the
> > > latter,
> > > but the former doesn't seem like it'd bring much to the
> table as
> > far as
> > > users are concerned, and for developers, it is an
> improvement,
> > but not
> > > a
> > > major one.
> > >
> > > Cheers,
> > >
> > > Chris
> > >
> > > On Fri, Apr 24, 2020 at 12:04 PM Andrew Schofield <
> > > schofieldandr...@gmail.com> wrote:
> > >
> > > > I wonder whether we're getting a bit overcomplicated with
> > this. I
> > > think all
> > > > that's required here is to add an optional guard
> predicate for
> > a
> > > > Transformation.
> > > > The predicate cannot end the Transformation chain, but
> it can
> > allow
> > > or
> > > > prevent a particular
> > > > Transformation from running.
> > > >
> > > > How about this as syntax?
> > > > transforms: extractInt
> > > > transforms.extractInt.?type:
> > > > org.apache.kafka.connect.predicates.TopicMatches
> > > > transforms.extractInt.?regex: my-prefix-.*
> > > > transforms.extractInt.type:
> > > > org.apache.kafka.connect.transforms.ExtractField$Key
> > > > transforms.extractInt.field: c1
> > > >
> > > > The idea is that a Transformation can have an optional
> > > RecordPredicate.
> > > > The RecordPredicate
> > > > can have configuration items, in a similar way to a
> > Transformation.
> > > The
> > > > syntax of
> > > > using a '?' prefix to separate configuration for the
> > RecordPredicate
> > > from
> > > > the configuration
> > > > for the Transformation could conceivably clash with an
> existing
> > > > Transformation
> > > > but the chances are minimal.
> > > >
> > > > This syntax doesn't allow for an 'else', but if the KIP
> offers
> > say a
> > > > TopicMatches predicate
> > > > then that can be configured to return FALSE if the
> predicate
> > matches.
> > > >
> > > > I feel that a DSL for SMTs is overkill. If you need
> something
> > that
> > > > complex, it's
> > > > perhaps too complex for a transformation chain and it's
> really
> > a
> > > streaming
> > > > application.
> > > >
> > > > Andrew Schofield
> > > > IBM Event Streams
> > > >
> > > > On 2020/04/08 21:39:31, Christopher Egerton <
> > chr...@confluent.io>
> > > wrote:
> > > > > Hi Tom,
> > > > >
> > > > > With regards to the potential Transformation::validate
> > method, I
> > > don't
> > > > > quite follow your objections. The AbstractHerder class,
> > > ConnectorConfig
> > > > > class, and embedding of ConfigDefs that happens with
> the two
> > is all
> > > > > internal logic and we're allowed to modify it however
> we
> > want, as
> > > long as
> > > > > it doesn't alter any public-facing APIs (and if it
> does, we
> > just
> > > have to
> > > > > document those changes in a KIP). We don't have to
> embed the
> > > ConfigDef
> > > > for
> > > > > a transformation chain inside another ConfigDef if the
> API
> > we want
> > > to
> > > > > present to our users doesn't play well with that part
> of the
> > code
> > > base.
> > > > > Additionally, beyond aligning with the existing API
> provided
> > for
> > > > > connectors, another advantage is that it becomes
> possible to
> > > validate
> > > > > properties for a configuration in the context of all
> other
> > > properties, so
> > > > > to be clear, it's not just about preserving what may be
> > perceived
> > > as a
> > > > > superficial similarity and comes with real functional
> > benefits
> > > that can't
> > > > > be provided (at least, not as easily) by dynamic
> > construction of a
> > > > > ConfigDef object.
> > > > >
> > > > > As far as the new proposal goes, I hate to say it, but
> I
> > think
> > > we're
> > > > stuck
> > > > > with the worst of both worlds here. Adding the new
> > RecordPredicate
> > > > > interface seems like it defeats the whole purpose of
> SMTs,
> > which
> > > is to
> > > > > allow manipulation of a connector's event stream by
> users
> > who don't
> > > > > necessarily know how or have the time to write Java
> code of
> > their
> > > own.
> > > > This
> > > > > is also why I'm in favor of adding a lightweight DSL
> for the
> > > condition;
> > > > > emphasizing readability for people who aren't very
> familiar
> > with
> > > Connect
> > > > > and just want to get something going quickly should be
> a
> > priority
> > > for
> > > > SMTs.
> > > > > But if that's not going to happen with this KIP, I'd
> still
> > choose
> > > the
> > > > > simpler, less-flexible approach initially outlined, in
> order
> > to
> > > keep
> > > > things
> > > > > simple for people creating connectors and try to let
> them
> > > accomplish what
> > > > > they want via configuration, not code.
> > > > >
> > > > > With regards to the question about where the line
> should be
> > drawn
> > > and how
> > > > > much is too much and comparisons to other stream
> processing
> > > frameworks, I
> > > > > think the nature of SMTs draws the line quite nicely:
> you
> > can only
> > > > process
> > > > > one message at a time. There's plenty of use cases out
> there
> > for
> > > > > heavier-duty processing frameworks like Kafka Streams,
> with
> > > aggregate
> > > > > operations, joining of streams, expanding a single
> message
> > into
> > > multiple
> > > > > messages, etc. With SMTs, none of this is possible; the
> > general
> > > use case
> > > > is
> > > > > to filter and clean a stream of data. If any of the
> > heavier-weight
> > > logic
> > > > > provided by, e.g., Streams, isn't required for a
> project, it
> > > should be
> > > > > possible to get along with just a collection of sink
> > connectors,
> > > source
> > > > > connectors, a converter or two, and SMTs that smooth
> over any
> > > differences
> > > > > in data format between what source connectors produce
> and
> > what sink
> > > > > connectors expect. This is why I'm comfortable
> suggesting
> > heavy
> > > expansion
> > > > > of the out-of-the-box SMTs that we provide with
> Connect; as
> > long as
> > > > they're
> > > > > reasonable to configure, they can greatly reduce the
> > operational
> > > burden
> > > > on
> > > > > anyone running and/or using a Connect cluster since
> they
> > might
> > > entirely
> > > > > replace additional services that would otherwise be
> required.
> > > > >
> > > > > All that said--this is a huge ask of someone who just
> wants
> > to
> > > support
> > > > the
> > > > > SMT equivalent of an "if" statement, and it's totally
> > > understandable if
> > > > > that's too much to ask. The one concern I have left is
> that
> > if we
> > > expand
> > > > > the SMT in the future, there become compatibility
> concerns
> > since
> > > SMTs are
> > > > > pretty tightly-coupled with the worker on which they
> run
> > (although
> > > > > technically, with some classpath/plugin path
> shuffling, you
> > can run
> > > > > different versions of the out-of-the-box SMTs from the
> > Connect
> > > worker on
> > > > > which they're run). Someone might write a connector
> config
> > with the
> > > > > If/Conditional/Whatever SMT with a condition type that
> works
> > on one
> > > > worker,
> > > > > but that doesn't work on another worker that's running
> an
> > earlier
> > > version
> > > > > of Connect. This is why I'm in favor of adding extra
> > predicates now
> > > > instead
> > > > > of later; if we're going to implement what has the
> potential
> > to be
> > > a bit
> > > > of
> > > > > a Swiss army knife SMT with room for future expansion
> of
> > > configuration,
> > > > and
> > > > > we can think of a reasonable way to add that
> functionality
> > now, it
> > > seems
> > > > > better for users and administrators of Connect to try
> to do
> > that
> > > now
> > > > > instead of later.
> > > > >
> > > > > Cheers,
> > > > >
> > > > > Chris
> > > > >
> > > > > On Wed, Apr 8, 2020 at 9:45 AM Tom Bentley <
> > tbent...@redhat.com>
> > > wrote:
> > > > >
> > > > > > Since no one objected I've updated the KIP with the
> > revised way
> > > to
> > > > > > configure this transformation.
> > > > > >
> > > > > > On Mon, Apr 6, 2020 at 2:52 PM Tom Bentley <
> > tbent...@redhat.com>
> > > > wrote:
> > > > > >
> > > > > > > To come back about a point Chris made:
> > > > > > >
> > > > > > > 1. Instead of the new "ConfigDef config(Map<String,
> > String>
> > > props)"
> > > > > > method,
> > > > > > >> what would you think about adopting a similar
> approach
> > as the
> > > > framework
> > > > > > >> uses with connectors, by adding a "Config
> > validate(Map<String,
> > > > String>
> > > > > > >> props)" method that can perform custom validation
> > outside of
> > > what
> > > > can be
> > > > > > >> performed by the ConfigDef's
> single-property-at-a-time
> > > validation?
> > > > It
> > > > > > may
> > > > > > >> be a little heavyweight for use with this
> particular
> > SMT, but
> > > it'd
> > > > > > provide
> > > > > > >> more flexibility for other SMT implementations
> and would
> > > mirror an
> > > > API
> > > > > > >> that
> > > > > > >> developers targeting the framework are likely
> already
> > > familiar with.
> > > > > > >>
> > > > > > >
> > > > > > > The validate() + config() approach taken for
> Connectors
> > > doesn't quite
> > > > > > work
> > > > > > > for Transformations.
> > > > > > >
> > > > > > > The default Connector.validate() basically just
> calls
> > > > > > > `config().validate(connectorConfigs)` and returns a
> > Config.
> > > > Separately
> > > > > > the
> > > > > > > AbstractHeader also calls `config()` and uses the
> Config
> > and
> > > > ConfigDef to
> > > > > > > build the ConfigInfos. The contract is not really
> > defined well
> > > > enough in
> > > > > > > the javadoc, but this means a connector can use
> > validate() to
> > > build
> > > > the
> > > > > > > ConfigDef which it will return from config().
> > > > > > >
> > > > > > > For Transformations we don't really want
> validate() to
> > perform
> > > > validation
> > > > > > > at all since ultimately the transformations config
> will
> > be
> > > embedded
> > > > in
> > > > > > the
> > > > > > > connector's and will be validated by the connector
> > itself. It
> > > > wouldn't be
> > > > > > > harmful if it _did_ perform validation, just
> > unnecessary. But
> > > having
> > > > a
> > > > > > > validate() method that ought not to validate()
> seems
> > like a
> > > recipe
> > > > for
> > > > > > > confusion.
> > > > > > >
> > > > > > > Also problematic is that there's no use for the
> Config
> > > returned from
> > > > > > > Transformations.validate().
> > > > > > >
> > > > > > > So I'm not convinced that the superficial
> similarity
> > really
> > > gains
> > > > > > anything.
> > > > > > >
> > > > > > > Kind regards,
> > > > > > >
> > > > > > > Tom
> > > > > > >
> > > > > > > On Mon, Apr 6, 2020 at 2:29 PM Tom Bentley <
> > > tbent...@redhat.com>
> > > > wrote:
> > > > > > >
> > > > > > >> Hi,
> > > > > > >>
> > > > > > >> Hi all,
> > > > > > >>
> > > > > > >> Thanks for the discussion so far.
> > > > > > >>
> > > > > > >> It seems a bit weird to me that when configuring
> the
> > > Conditional SMT
> > > > > > with
> > > > > > >> a DSL you would use a concise, intuitive DSL for
> > expressing
> > > the
> > > > > > condition,
> > > > > > >> but not for the transforms that it's guarding. It
> also
> > seems
> > > > natural, if
> > > > > > >> you support this for conditionally applying SMTs,
> that
> > you'd
> > > soon
> > > > want
> > > > > > to
> > > > > > >> support the same thing for a generic filter
> transformer.
> > > Then, if
> > > > you
> > > > > > can
> > > > > > >> configure a filter transformation using this DSL,
> it
> > becomes
> > > odd
> > > > that
> > > > > > you
> > > > > > >> can't do this for mapping transformations. I
> think it
> > would
> > > be a
> > > > > > mistake to
> > > > > > >> go specifying an expression language for
> conditions when
> > > really that
> > > > > > might
> > > > > > >> just be part of a language for transformations.
> > > > > > >>
> > > > > > >> I think it would be possible today to write an
> SMT which
> > > allowed
> > > > you to
> > > > > > >> express the transformation in a DSL. Concretely,
> it's
> > > possible to
> > > > > > imagine a
> > > > > > >> single transformation taking a DSL something like
> this:
> > > > > > >>
> > > > > > >> compose(
> > > > > > >> Flatten.Key(delimiter: ':'),
> > > > > > >> If(condition: TopicMatches(pattern:
> "blah-.*"),
> > > > > > >> then: Flatten.Value(delimiter: '/')))
> > > > > > >>
> > > > > > >> All I've really done here, beyond what was already
> > proposed,
> > > is
> > > > rename
> > > > > > >> Conditional to If, imagine a couple more bits of
> syntax
> > > > > > >> (SMTs being constructed by class name and named
> argument
> > > invocation
> > > > > > >> syntax to support SMT constructors) and add a
> higher
> > level
> > > compose()
> > > > > > >> function for chaining SMTs (which could easily be
> > replaced
> > > with
> > > > brace
> > > > > > >> delimited blocks).
> > > > > > >>
> > > > > > >> That may be a discussion we should have, but I
> think in
> > > _this_ KIP
> > > > we
> > > > > > >> should focus on the conditional part, since the
> above
> > example
> > > > hopefully
> > > > > > >> shows that it would be possible to reuse it in a
> DSL if
> > there
> > > was
> > > > > > appetite
> > > > > > >> for that.
> > > > > > >>
> > > > > > >> With that in mind, and since my original
> suggestion for
> > an
> > > > abbreviated
> > > > > > >> config syntax didn't appeal to people, I propose
> that we
> > > stick with
> > > > the
> > > > > > >> existing norms for configuring this.
> > > > > > >> The previous example would look like this:
> > > > > > >>
> > > > > > >> transformation: flattenKey,if
> > > > > > >> transformation.flattenKey.type: Flatten.Key
> > > > > > >> transformation.flattenKey.delimiter: :
> > > > > > >> transformation.if.type: If
> > > > > > >> transformation.if.condition.type: TopicMatches
> > > > > > >> transformation.if.condition.pattern: blah-.*
> > > > > > >> transformation.if.then: flattenValue
> > > > > > >> transformation.if.then.flattenValue.type:
> Flatten.Value
> > > > > > >> transformation.if.then.flattenValue.delimiter: /
> > > > > > >>
> > > > > > >> Also, I'm inclined to think we should stick to
> just
> > supporting
> > > > > > >> TopicMatches and Not, since we've not identified
> an
> > actual
> > > need for
> > > > > > >> 'has-header', 'or' and 'and'.
> > > > > > >>
> > > > > > >> An example of the usage of Not would look like
> this:
> > > > > > >>
> > > > > > >> transformation: flattenKey,if
> > > > > > >> transformation.flattenKey.type: Flatten.Key
> > > > > > >> transformation.flattenKey.delimiter: :
> > > > > > >> transformation.if.type: If
> > > > > > >> transformation.if.condition.type: Not
> > > > > > >> transformation.if.condition.operand:
> startsWithBlah
> > > > > > >>
> transformation.if.condition.operand.startsWithBlah.type:
> > > > TopicMatches
> > > > > > >>
> > transformation.if.condition.operand.startsWithBlah.pattern:
> > > blah-.*
> > > > > > >> transformation.if.then: flattenValue
> > > > > > >> transformation.if.then.flattenValue.type:
> Flatten.Value
> > > > > > >> transformation.if.then.flattenValue.delimiter: /
> > > > > > >>
> > > > > > >> Hopefully we can agree that this allows the
> conditional
> > SMT
> > > part to
> > > > make
> > > > > > >> progress without getting bogged down.
> > > > > > >>
> > > > > > >> Thoughts? If this seems broadly reasonable, I'll
> update
> > the
> > > KIP.
> > > > > > >>
> > > > > > >> Kind regards,
> > > > > > >>
> > > > > > >> Tom
> > > > > > >>
> > > > > > >> On Fri, Apr 3, 2020 at 5:55 PM Gunnar Morling <
> > > gun...@hibernate.org
> > > > >
> > > > > > >> wrote:
> > > > > > >>
> > > > > > >>> Hi all,
> > > > > > >>>
> > > > > > >>> Thanks a lot for this initiative, Tom!
> > > > > > >>>
> > > > > > >>> To shed some light, the use case where this
> first came
> > up,
> > > were
> > > > issues
> > > > > > >>> we saw with SMTs being applied to the different
> topics
> > > produced by
> > > > the
> > > > > > >>> Debezium change data capture connectors. There
> are
> > different
> > > kinds
> > > > of
> > > > > > >>> topics (for change data, schema history,
> heartbeats
> > etc.)
> > > and the
> > > > > > >>> record structure to expect may vary between
> those.
> > Hence we
> > > saw
> > > > issues
> > > > > > >>> with SMTs like ExtractField, which for instance
> only
> > should
> > > be
> > > > applied
> > > > > > >>> to all change data topics but not the other ones.
> > > > > > >>>
> > > > > > >>> I like the overall approach; for Debezium's
> purposes,
> > the
> > > simple
> > > > topic
> > > > > > >>> matching and negation operators would be
> sufficient
> > already.
> > > I
> > > > agree
> > > > > > >>> with Chris and would prefer one single condition
> > attribute,
> > > which
> > > > > > >>> contains a single condition or potentially a
> logical
> > > expression
> > > > with
> > > > > > >>> not, and, etc. I think it's less ambiguous, in
> > particular
> > > when it
> > > > > > >>> comes to ordering of the different conditions and
> > > determining their
> > > > > > >>> precedence.
> > > > > > >>>
> > > > > > >>> Would love to see this feature in one or another
> way in
> > > Connect.
> > > > > > >>>
> > > > > > >>> Best,
> > > > > > >>>
> > > > > > >>> --Gunnar
> > > > > > >>>
> > > > > > >>>
> > > > > > >>>
> > > > > > >>> Am Do., 2. Apr. 2020 um 18:48 Uhr schrieb Tom
> Bentley <
> > > > > > >>> tbent...@redhat.com>:
> > > > > > >>> >
> > > > > > >>> > Hi Chris and Sönke,
> > > > > > >>> >
> > > > > > >>> > Using the numbering from Chris's email...
> > > > > > >>> >
> > > > > > >>> > 1. That's a good point, I'll see what is
> needed to
> > make
> > > that
> > > > work.
> > > > > > >>> >
> > > > > > >>> > 2. I'm happy enough to add support for "and"
> and
> > "or" as
> > > part of
> > > > this
> > > > > > >>> KIP
> > > > > > >>> > if people can see a need for it.
> > > > > > >>> >
> > > > > > >>> > In a similar vein, I was wondering about
> whether it
> > would
> > > be
> > > > > > worthwhile
> > > > > > >>> > having the equivalent of an "else" clause
> (what's in
> > the
> > > KIP is
> > > > > > >>> basically
> > > > > > >>> > an "if" statement). Without support for "else"
> I
> > think
> > > people
> > > > would
> > > > > > >>> often
> > > > > > >>> > need two conditionals, with the condition of
> one
> > being the
> > > > negation
> > > > > > of
> > > > > > >>> the
> > > > > > >>> > condition of another.
> > > > > > >>> >
> > > > > > >>> > 3. I can see the attraction of an expression
> > language. The
> > > pros
> > > > > > include
> > > > > > >>> > being terse and familiar to programmers and
> > potentially
> > > very
> > > > flexible
> > > > > > >>> if
> > > > > > >>> > that's needed in the future. I had a play and
> > implemented
> > > it
> > > > using
> > > > > > >>> ANTLR
> > > > > > >>> > and it's not difficult to write a grammar and
> > implement the
> > > > functions
> > > > > > >>> we've
> > > > > > >>> > already discussed and get decent error
> messages when
> > the
> > > > expression
> > > > > > is
> > > > > > >>> > malformed. So on the one hand I quite like the
> idea.
> > On
> > > the other
> > > > > > hand
> > > > > > >>> it
> > > > > > >>> > feels like overkill for the use cases that have
> > actually
> > > been
> > > > > > >>> identified so
> > > > > > >>> > far.
> > > > > > >>> >
> > > > > > >>> > @Sönke what do you make of the expression
> language
> > idea?
> > > > > > >>> >
> > > > > > >>> > Kind regards,
> > > > > > >>> >
> > > > > > >>> > Tom
> > > > > > >>> >
> > > > > > >>> > On Wed, Apr 1, 2020 at 9:49 PM Christopher
> Egerton <
> > > > > > >>> chr...@confluent.io>
> > > > > > >>> > wrote:
> > > > > > >>> >
> > > > > > >>> > > Hi Tom,
> > > > > > >>> > >
> > > > > > >>> > > This looks great and I'd love to see the
> > out-of-the-box
> > > SMTs
> > > > become
> > > > > > >>> even
> > > > > > >>> > > more powerful with the improvements you've
> > proposed! Got
> > > a few
> > > > > > >>> remarks and
> > > > > > >>> > > would be interested in your thoughts:
> > > > > > >>> > >
> > > > > > >>> > > 1. Instead of the new "ConfigDef
> config(Map<String,
> > > String>
> > > > props)"
> > > > > > >>> method,
> > > > > > >>> > > what would you think about adopting a similar
> > approach
> > > as the
> > > > > > >>> framework
> > > > > > >>> > > uses with connectors, by adding a "Config
> > > validate(Map<String,
> > > > > > >>> String>
> > > > > > >>> > > props)" method that can perform custom
> validation
> > > outside of
> > > > what
> > > > > > >>> can be
> > > > > > >>> > > performed by the ConfigDef's
> > single-property-at-a-time
> > > > validation?
> > > > > > >>> It may
> > > > > > >>> > > be a little heavyweight for use with this
> > particular
> > > SMT, but
> > > > it'd
> > > > > > >>> provide
> > > > > > >>> > > more flexibility for other SMT
> implementations and
> > would
> > > > mirror an
> > > > > > >>> API that
> > > > > > >>> > > developers targeting the framework are likely
> > already
> > > familiar
> > > > > > with.
> > > > > > >>> > > 2. The possibility for adding the logical
> operators
> > > "and" and
> > > > "or"
> > > > > > is
> > > > > > >>> > > mentioned, but only as a potential future
> change
> > and not
> > > one
> > > > > > >>> proposed by
> > > > > > >>> > > this KIP. Why not include those operators
> sooner
> > rather
> > > than
> > > > later?
> > > > > > >>> > > 3. The syntax for named conditions that are
> then
> > > referenced in
> > > > > > >>> logical
> > > > > > >>> > > operators is... tricky. It took me a few
> attempts
> > to
> > > grok the
> > > > > > example
> > > > > > >>> > > provided in the KIP after reading Sönke's
> question
> > about
> > > the
> > > > > > example
> > > > > > >>> for
> > > > > > >>> > > negation. What about a more sophisticated
> but less
> > > verbose
> > > > syntax
> > > > > > >>> that
> > > > > > >>> > > supports a single configuration for the
> condition,
> > even
> > > with
> > > > > > logical
> > > > > > >>> > > operators? I'm thinking something like
> > > > > > >>> > > "transforms.conditionalExtract.condition:
> > > > > > not(has-header:my-header)"
> > > > > > >>> > > instead of the
> > "transforms.conditionalExtract.condition:
> > > > > > >>> not:hasMyHeader"
> > > > > > >>> > > and
> > "transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> > > has-header:my-header" properties. If support
> for a
> > > logical
> > > > "and" is
> > > > > > >>> added,
> > > > > > >>> > > this could then be expanded to something like
> > > > > > >>> > > "transforms.conditionalExtract.condition:
> > > > > > and(has-header(my-header),
> > > > > > >>> > > not(topic-matches(my-prefix-.*)))". There
> would be
> > > additional
> > > > > > >>> complexity
> > > > > > >>> > > here with the need to escape parentheses and
> > commas that
> > > are
> > > > > > >>> intended to be
> > > > > > >>> > > treated literally (as part of a header name,
> for
> > example)
> > > > instead
> > > > > > of
> > > > > > >>> as
> > > > > > >>> > > part of the syntax for the condition itself,
> but a
> > little
> > > > > > additional
> > > > > > >>> > > complexity for edge cases like that may be
> > warranted if
> > > it
> > > > heavily
> > > > > > >>> reduces
> > > > > > >>> > > complexity for the common cases. The
> rationale for
> > the
> > > proposed
> > > > > > >>> > > parentheses-based syntax here instead of
> what's
> > > mentioned in
> > > > the
> > > > > > KIP
> > > > > > >>> > > (something like "and: <condition1>,
> <condition2>")
> > is to
> > > help
> > > > with
> > > > > > >>> > > readability; we probably wouldn't need that
> with
> > the
> > > approach
> > > > of
> > > > > > >>> naming
> > > > > > >>> > > conditions via separate properties, but
> things may
> > get a
> > > little
> > > > > > >>> nasty with
> > > > > > >>> > > literal conditions included there,
> especially with
> > the
> > > > possibility
> > > > > > of
> > > > > > >>> > > nesting. Finally, the shift in syntax here
> should
> > make it
> > > > easier to
> > > > > > >>> handle
> > > > > > >>> > > cases like the header value matching brought
> up by
> > > Sönke; it
> > > > might
> > > > > > >>> look
> > > > > > >>> > > something like "header-matches(header-name,
> > > > header-value-pattern)".
> > > > > > >>> > >
> > > > > > >>> > > Cheers,
> > > > > > >>> > >
> > > > > > >>> > > Chris
> > > > > > >>> > >
> > > > > > >>> > > On Wed, Apr 1, 2020 at 9:00 AM Tom Bentley <
> > > > tbent...@redhat.com>
> > > > > > >>> wrote:
> > > > > > >>> > >
> > > > > > >>> > > > Hi Sönke,
> > > > > > >>> > > >
> > > > > > >>> > > > Thanks for taking a look.
> > > > > > >>> > > >
> > > > > > >>> > > > Let me answer in reverse order, since I
> think it
> > might
> > > make
> > > > more
> > > > > > >>> sense
> > > > > > >>> > > that
> > > > > > >>> > > > way...
> > > > > > >>> > > >
> > > > > > >>> > > > Also, while writing that, I noticed that
> you
> > have a
> > > version
> > > > with
> > > > > > >>> and
> > > > > > >>> > > > > without "name" for your transformation
> in the
> > KIP:
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> > > has-header:my-header
> > > > > > >>> > > > > and
> > > > > > >>> > > > > transforms.conditionalExtract.condition:
> > > > has-header:my-header
> > > > > > >>> > > > >
> > > > > > >>> > > >
> > > > > > >>> > > > The example
> > > > > > >>> > > >
> transforms.conditionalExtract.condition:
> > > > has-header:my-header
> > > > > > >>> > > > is a "has-header" condition (the prefix of
> the
> > config
> > > value),
> > > > > > >>> which will
> > > > > > >>> > > > match records with a "my-header" header
> (given
> > in the
> > > > suffix).
> > > > > > >>> > > >
> > > > > > >>> > > > The other example given is:
> > > > > > >>> > > >
> transforms.conditionalExtract.condition:
> > > not:hasMyHeader
> > > > > > >>> > > >
> > > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> > > > has-header:my-header
> > > > > > >>> > > > The root of the condition is a "not"
> condition
> > (the
> > > prefix
> > > > of the
> > > > > > >>> value
> > > > > > >>> > > for
> > > > > > >>> > > > the
> transforms.conditionalExtract.condition key)
> > of
> > > another
> > > > named
> > > > > > >>> > > condition
> > > > > > >>> > > > called "hasMyHeader" (the suffix). Any name
> > could be
> > > used
> > > > for the
> > > > > > >>> other
> > > > > > >>> > > > condition. That other condition is
> configured at
> > > > > > >>> > > >
> > > "transforms.conditionalExtract.condition.<conditionName>".
> > > > That
> > > > > > >>> condition
> > > > > > >>> > > > is a "has-header" condition (the prefix),
> which
> > will
> > > match
> > > > > > records
> > > > > > >>> with a
> > > > > > >>> > > > "my-header" header (given in the suffix).
> So the
> > > > "has-header:"
> > > > > > >>> condition
> > > > > > >>> > > > type would always require a suffix, as
> would the
> > "not:"
> > > > condition
> > > > > > >>> type.
> > > > > > >>> > > > Hypothetically you could have a "true"
> condition
> > type
> > > (which
> > > > > > would
> > > > > > >>> not
> > > > > > >>> > > > require a suffix), and the hypothetical
> binary
> > > conditions
> > > > "and:"
> > > > > > >>> and
> > > > > > >>> > > "or:"
> > > > > > >>> > > > would require a pair of other condition
> names.
> > > > > > >>> > > >
> > > > > > >>> > > > So what's proposed is a scheme for encoding
> > conditions
> > > where
> > > > the
> > > > > > >>> > > condition
> > > > > > >>> > > > type is the prefix of the value of some
> > "....condition"
> > > > config
> > > > > > >>> key, and
> > > > > > >>> > > the
> > > > > > >>> > > > optional suffix provides parameters for the
> > condition.
> > > This
> > > > makes
> > > > > > >>> those
> > > > > > >>> > > > parameters a bit inflexible, but is
> relatively
> > > succinct.
> > > > > > >>> > > >
> > > > > > >>> > > > This leads on to your first point. You're
> right
> > that
> > > use
> > > > cases
> > > > > > >>> might
> > > > > > >>> > > appear
> > > > > > >>> > > > which need other conditions, and we should
> make
> > it
> > > flexible
> > > > > > enough
> > > > > > >>> to be
> > > > > > >>> > > > able to cope with future use cases. On the
> other
> > hand,
> > > I was
> > > > > > >>> concerned
> > > > > > >>> > > that
> > > > > > >>> > > > we end up with something which is quite
> > complicated to
> > > > configure.
> > > > > > >>> (There
> > > > > > >>> > > > comes a point where it might makes more
> sense
> > for the
> > > user to
> > > > > > >>> write their
> > > > > > >>> > > > own SMT).
> > > > > > >>> > > >
> > > > > > >>> > > > Just of the top of my head it might look
> like:
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> type:has-header
> > > > > > >>> > > > >
> > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> > > > header-name:my-header
> > > > > > >>> > > > >
> > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> > > field-value:my-value
> > > > > > >>> > > > >
> > > > > > >>> > > >
> > > > > > >>> > > > That won't work because the format is
> basically a
> > > > > > >>> Properties/Map<String,
> > > > > > >>> > > > String> and what you've suggested has
> duplicate
> > keys.
> > > > > > >>> > > >
> > > > > > >>> > > > One thing I did briefly consider what the
> > ability to
> > > treat
> > > > > > >>> conditions as
> > > > > > >>> > > > Configurable objects in their own right
> (opening
> > up the
> > > > > > >>> possibility of
> > > > > > >>> > > > people supplying their own Conditions,
> just like
> > they
> > > can
> > > > supply
> > > > > > >>> their
> > > > > > >>> > > own
> > > > > > >>> > > > SMTs). That might be configured something
> like
> > this:
> > > > > > >>> > > >
> > > > > > >>> > > >
> transforms.conditionalExtract.condition: not
> > > > > > >>> > > >
> > transforms.conditionalExtract.condition.not.type:
> > > Not
> > > > > > >>> > > >
> > > transforms.conditionalExtract.condition.not.negated: foo
> > > > > > >>> > > >
> > transforms.conditionalExtract.condition.foo.type:
> > > > > > >>> HasHeaderWithValue
> > > > > > >>> > > >
> > transforms.conditionalExtract.condition.foo.header:
> > > > my-header
> > > > > > >>> > > >
> > transforms.conditionalExtract.condition.foo.value:
> > > > my-value
> > > > > > >>> > > >
> > > > > > >>> > > > I didn't propose that I couldn't see the
> use
> > cases to
> > > justify
> > > > > > this
> > > > > > >>> kind
> > > > > > >>> > > of
> > > > > > >>> > > > complexity, especially as the common case
> would
> > surely
> > > be
> > > > > > matching
> > > > > > >>> > > against
> > > > > > >>> > > > topic name (to be honest I wasn't
> completely
> > convinced
> > > by the
> > > > > > need
> > > > > > >>> for
> > > > > > >>> > > > "has-header"). In the current version of
> the KIP
> > > that's just
> > > > > > >>> > > >
> > > > > > >>> > > >
> transforms.conditionalExtract.condition:
> > > topic-matches:
> > > > > > >>> my-prefix-.*
> > > > > > >>> > > >
> > > > > > >>> > > > but using the more flexible scheme that
> would
> > require
> > > > something
> > > > > > >>> more like
> > > > > > >>> > > > this:
> > > > > > >>> > > >
> > > > > > >>> > > >
> transforms.conditionalExtract.condition: bar
> > > > > > >>> > > >
> > transforms.conditionalExtract.condition.bar.type:
> > > > TopicMatch
> > > > > > >>> > > >
> > > transforms.conditionalExtract.condition.bar.pattern:
> > > > > > >>> my-prefix-.*
> > > > > > >>> > > >
> > > > > > >>> > > > If people know of use cases which would
> justify
> > more
> > > > > > >>> sophistication, I'm
> > > > > > >>> > > > happy to reconsider.
> > > > > > >>> > > >
> > > > > > >>> > > > Thanks again for taking a look!
> > > > > > >>> > > >
> > > > > > >>> > > > Tom
> > > > > > >>> > > >
> > > > > > >>> > > > On Wed, Apr 1, 2020 at 2:05 PM Sönke Liebau
> > > > > > >>> > > > <soenke.lie...@opencore.com.invalid>
> wrote:
> > > > > > >>> > > >
> > > > > > >>> > > > > Hi Tom,
> > > > > > >>> > > > >
> > > > > > >>> > > > > sounds useful to me, thanks for the KIP!
> > > > > > >>> > > > > The only thought that I had while
> reading was
> > that
> > > this
> > > > will
> > > > > > >>> probably
> > > > > > >>> > > > raise
> > > > > > >>> > > > > questions about more involved conditions
> fairly
> > > quickly.
> > > > For
> > > > > > >>> example
> > > > > > >>> > > the
> > > > > > >>> > > > > "has-header" will cause an appetite for
> > conditions
> > > like
> > > > > > >>> > > > > "this-header-has-that-value".
> > > > > > >>> > > > > This would necessitate two parameters to
> be
> > passed
> > > into the
> > > > > > >>> condition,
> > > > > > >>> > > > > which I think is not currently included
> in the
> > KIP.
> > > I am
> > > > not
> > > > > > >>> saying add
> > > > > > >>> > > > > this now, but might it make sense to
> discuss a
> > > concept of
> > > > how
> > > > > > >>> that
> > > > > > >>> > > might
> > > > > > >>> > > > > look now, to avoid potential changes
> later on.
> > > > > > >>> > > > >
> > > > > > >>> > > > > Just of the top of my head it might look
> like:
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> type:has-header
> > > > > > >>> > > > >
> > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> > > > header-name:my-header
> > > > > > >>> > > > >
> > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> > > field-value:my-value
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > > > > > >>> > > > > Also, while writing that, I noticed that
> you
> > have a
> > > version
> > > > > > with
> > > > > > >>> and
> > > > > > >>> > > > > without "name" for your transformation
> in the
> > KIP:
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > transforms.conditionalExtract.condition.hasMyHeader:
> > > > > > >>> > > has-header:my-header
> > > > > > >>> > > > > and
> > > > > > >>> > > > > transforms.conditionalExtract.condition:
> > > > has-header:my-header
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > > > > > >>> > > > > Is this intentional and the name is
> optional?
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > > > > > >>> > > > > Best regards,
> > > > > > >>> > > > >
> > > > > > >>> > > > > Sönke
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > > > > > >>> > > > > On Wed, 1 Apr 2020 at 11:12, Tom Bentley
> <
> > > > tbent...@redhat.com>
> > > > > > >>> wrote:
> > > > > > >>> > > > > >
> > > > > > >>> > > > > > Does anyone have any comments,
> feedback or
> > > thoughts about
> > > > > > this?
> > > > > > >>> > > > > >
> > > > > > >>> > > > > > Thanks,
> > > > > > >>> > > > > >
> > > > > > >>> > > > > > Tom
> > > > > > >>> > > > > >
> > > > > > >>> > > > > > On Tue, Mar 24, 2020 at 11:56 AM Tom
> Bentley
> > <
> > > > > > >>> tbent...@redhat.com>
> > > > > > >>> > > > > wrote:
> > > > > > >>> > > > > >
> > > > > > >>> > > > > > > Hi,
> > > > > > >>> > > > > > >
> > > > > > >>> > > > > > > I've opened KIP-585 which is
> intended to
> > provide
> > > a
> > > > > > mechanism
> > > > > > >>> to
> > > > > > >>> > > > > > > conditionally apply SMTs in Kafka
> Connect.
> > I'd be
> > > > grateful
> > > > > > >>> for any
> > > > > > >>> > > > > > > feedback:
> > > > > > >>> > > > > > >
> > > > > > >>> > > > >
> > > > > > >>> > > > >
> > > > > > >>> > > >
> > > > > > >>> > >
> > > > > > >>>
> > > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-585%3A+Conditional+SMT
> > > > > > >>> > > > > > >
> > > > > > >>> > > > > > > Many thanks,
> > > > > > >>> > > > > > >
> > > > > > >>> > > > > > > Tom
> > > > > > >>> > > > > > >
> > > > > > >>> > > > >
> > > > > > >>> > > >
> > > > > > >>> > >
> > > > > > >>>
> > > > > > >>>
> > > > > >
> > > > >
> > > >
> > >
> > >
> >
> >
>
>
