Again, great feedback Chris. Much appreciated.
Added my comments below:
On Tue, 5 Apr 2022 at 20:22, Chris Egerton <fearthecel...@gmail.com> wrote:
> Hi Jorge,
>
> Looking good! I have a few comments left but all but one or two are minor.
>
> 1. The motivation section states "This KIP is aimed to include support for
> nested structures on the existing SMTs... and to include the abstractions
> to reuse this in future SMTs". A good implementation of this KIP will
> definitely isolate reusable logic into a separate abstraction that can be
> easily pulled in to the SMTs we want to add nested field support to, but
> unless we plan on making this kind of abstraction publicly available as
> some kind of utility method or class that external SMT developers can
> leverage, we can probably leave this part out as it's more of an
> implementation detail.
>
Make sense, will leave this out of the KIP.
>
> 2. The Cast example is a little misleading, isn't it? It demonstrates the
> escape syntax for fields with dot literals in their names, but it doesn't
> demonstrate a way to actually use the Cast (or any other) SMT to access a
> nested field in a record, which is the whole point of the KIP. I like the
> example of escape syntax but we should probably also add one for nested
> field access.
>
Agree. I have added examples to each SMT to be more clear about how it
affects each function
.
>
> 3. With the InsertField SMT, I'm wondering what the specific behavior will
> be when some or all of the "middle layer" nested fields are missing. For
> example, if I have a record with a value of { "k1": "v1 } and I apply
> InsertField with topic.field = n1.n2.n3.topic, what will happen? Will the
> updated value become { "k1": "v1", "n1": { "n2": { "n3": "topic" }}}, will
> an exception be thrown, or something else? This seems analogous to the
> command line mkdir command, which (at least on some operating systems)
> fails by default if you try to create a new nested directory where anything
> but the last element in the path doesn't exist, but can be invoked with a
> flag that instructs it to go ahead and create all levels of nested
> directory instead. I'm leaning on the side of "just create everything" but
> would be interested in your thoughts, and either way, we should probably
> make sure the intended behavior is well-defined before voting.
>
This is an interesting case, thanks for catching this!
The default behavior I see is to create parents if they are missing and
overwrite fields
if they already exist.
I'm planning to include the following two flags if there is a need to
overwrite this behavior:
- `on_missing_parent` = (CREATE|IGNORE), default=CREATE
- `on_existing_field` = (OVERWRITE|IGNORE), default=OVERWRITE
>
> 4. Similarly, what will the behavior be if any of the field elements
> specified with InsertField already exist in the record value? Will we just
> overwrite them? What's the behavior of InsertField today under similar
> circumstances?
>
The current behavior is to overwrite the value.
>
> Cheers,
>
> Chris
>
> On Thu, Mar 31, 2022 at 4:15 PM Jorge Esteban Quilcate Otoya <
> quilcate.jo...@gmail.com> wrote:
>
> > Thanks, Chris! Much appreciated all the feedback here.
> >
> > 1. You nailed it setting the design goal here: "it shouldn't be
> impossible
> > to use this new feature for any field name, no matter how convoluted.
> It's
> > fine if edge cases introduce difficulty (such as less-readable
> > configurations), but it's not fine if they can't be addressed at all."
> > Back to the previous proposals (using only dots as separators) we have 2
> > alternatives:
> > 1. escaping with backslashes
> > 2. escaping with dots itself
> >
> > I'll lean for alternative 2, as you proposed before. Feels to me that
> > backslashes have more potential to lead to confusion in JSON configs, and
> > CSV seems like a good precedent to use the same character to escape
> itself.
> > KIP is updated to reflect this.
> >
> > 2. Thanks! I'll add an example, and stick with the current approach
> > defining the style per individual transform configuration.
> >
> > 3. Yes, thanks! KIP updated.
> >
> > 4. Of course. KIP updated.
> >
> > On Mon, 28 Mar 2022 at 21:59, Chris Egerton <fearthecel...@gmail.com>
> > wrote:
> >
> > > Hi Jorge,
> > >
> > > Thanks for addressing my comments; the KIP looks up-to-date and pretty
> > > readable now, and the rejected alternatives section does a great job of
> > > outlining the discussion so far and providing context for anyone else
> who
> > > might want to join in.
> > >
> > > 1. Thoughts on choice of delimiter:
> > > - I like the optimization for simple cases, but I think the new
> proposal
> > is
> > > a little too restrictive. What if there's a field whose name contains
> all
> > > of the permitted options (currently just ".", ",", and "/")?
> > > - If we expand the set of permitted delimiters to allow for any
> > > single-character string, configuration complexity will increase and
> > > readability may decrease
> > > - Also worth pointing out that there is some convention for doubling a
> > > delimiter character as an escape mechanism with formats like CSV [1]
> > > - Overall I think we may be approaching the saturation point for
> > productive
> > > discussion on delimiter syntax so I don't want to spend too much more
> of
> > > your time on it. I think the one point I'd like to leave for now is
> that
> > it
> > > shouldn't be impossible to use this new feature for any field name, no
> > > matter how convoluted. It's fine if edge cases introduce difficulty
> (such
> > > as less-readable configurations), but it's not fine if they can't be
> > > addressed at all.
> > >
> > > 2.
> > > The configuration style where you define "transforms.field.style" in
> the
> > > connector config, and then this applies to all SMTs for the connector,
> is
> > > very interesting. However, it doesn't follow convention for existing
> > SMTs.
> > > Right now, if you want to configure an SMT, you define its name in the
> > > connector config (for example, "transforms": "smt1"), and then define
> all
> > > of the properties for that SMT in the connector config using a
> > namespacing
> > > mechanism specific to that SMT (for example, "transforms.smt1.prop1":
> > > "val1"). That SMT then sees only the properties defined in that
> > namespace,
> > > with the prefix stripped (for example, "prop1": "val1") in its
> configure
> > > [2] [3] method.
> > > If we want to continue to follow this convention, then instead of
> > > specifying "transforms.field.style" in a connector config, we would
> > expect
> > > users to configure "transforms.<name>.field.style", for each SMT that
> > they
> > > want to configure a field style for. This would require more work on
> the
> > > part of the user, but would be simpler to reason about and easier to
> > > implement.
> > > If we want to explore an alternative where users can specify global
> > > properties that apply to all transforms in a connector config, then the
> > > semantics for this need to be defined in the KIP. This would have to
> > > include whether this will apply only for the special case of the
> > > "field.style" and possibly "field.separator" properties or if it would
> be
> > > available more generally for other properties, whether it will apply
> only
> > > for the SMTs outlined in the KIP or if the "field.style" and possibly
> > > "field.separator" properties would also be passed into custom SMTs so
> > that
> > > they could choose to act on them if applicable, how edge cases like
> > having
> > > an SMT named "field" in your connector config would be handled, etc.
> > > Either way, it might help to have an example in the KIP outlining how
> one
> > > of the to-be-augmented SMTs can be configured with this new feature
> and a
> > > before/after of how a record value would be transformed with that
> > > configuration.
> > >
> > > 3. The docstring for the "transforms.field.style" property mentions
> that
> > > the permitted values are "plain" and "nested", but then describes
> > behavior
> > > with a value of "root". Should that be "plain" instead?
> > >
> > > 4. The docstring for the "transforms.field.separator" property
> > exclusively
> > > mentions structs, but the feature is intended to work with maps as
> well.
> > > Can we update it to reflect this?
> > >
> > > References:
> > >
> > > [1] - https://stackoverflow.com/a/17808731
> > > [2] -
> > >
> > >
> >
> https://github.com/apache/kafka/blob/7243facb8d69a7252e6b9556b5eaee13e41bab7f/connect/api/src/main/java/org/apache/kafka/connect/transforms/Transformation.java#L30
> > > [3] -
> > >
> > >
> >
> https://github.com/apache/kafka/blob/7243facb8d69a7252e6b9556b5eaee13e41bab7f/clients/src/main/java/org/apache/kafka/common/Configurable.java#L26-L29
> > >
> > > Cheers,
> > >
> > > Chris
> > >
> > > On Mon, Mar 28, 2022 at 1:32 PM Jorge Esteban Quilcate Otoya <
> > > quilcate.jo...@gmail.com> wrote:
> > >
> > > > Thanks, Chris!
> > > >
> > > > 1. I'd argue "this..field.child" could be harder to grasp than
> > > > "this.field/child" + separator: "/".
> > > > Even though this represents additional information, it follows a
> > similar
> > > > approach as the "Flatten#delimeter" configuration.
> > > > I want to give the separator approach another try, so I have updated
> > the
> > > > KIP with the separator proposal, sticking to only 2 alternatives that
> > > > should hopefully cover most scenarios.
> > > >
> > > > 2. Agree. KIP has been updated with this improvement.
> > > >
> > > > 3. You're right. I have updated this section accordingly.
> > > >
> > > > 4. Good catch! I've replaced it with `DropHeaders`.
> > > >
> > > > Looking forward to your feedback.
> > > >
> > > > Thanks,
> > > > Jorge.
> > > >
> > > > On Wed, 9 Mar 2022 at 21:33, Chris Egerton <fearthecel...@gmail.com>
> > > > wrote:
> > > >
> > > > > Hi Jorge,
> > > > >
> > > > > Looking good! Got a few more thoughts.
> > > > >
> > > > > 1. Sorry to revisit this, but I think we may want to adopt a
> slightly
> > > > > different escape syntax style. Backslashes are great, but since
> > they're
> > > > > already used by JSON, using them as an escape sequence in field
> > > notation
> > > > > would also lead to some pretty ugly connector configs. Anyone who's
> > had
> > > > to
> > > > > write regular expressions with backslashes in Java is probably
> > already
> > > > > familiar with this: "this\\\\.is\\\\.not\\\\.very\\\\.readable".
> What
> > > do
> > > > > you think about using the dot character to escape itself? In other
> > > words,
> > > > > to access a single field named "this.field", instead of using the
> > > syntax
> > > > > "this\.field" (which in JSON would have to be expressed as
> > > > "this\\.field"),
> > > > > we could use "this..field", and for a single field named
> > "this\field",
> > > > > instead of using the syntax "this\\field" (or, in JSON,
> > > "this\\\\field"),
> > > > > we could use "this\field" (or, in JSON, "this\\field").
> > > > >
> > > > > 2. Could you flesh out the details on the new "field.style"
> property,
> > > > > including the type, default value, importance, and a preliminary
> > > > docstring?
> > > > > See
> > > > >
> > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-618%3A+Exactly-Once+Support+for+Source+Connectors#KIP618:ExactlyOnceSupportforSourceConnectors-Newproperties
> > > > > for an example.
> > > > >
> > > > > 3. Is the "Compatibility, Deprecation, and Migration Plan" section
> > > still
> > > > > accurate after the latest update? Seems like it's still written
> with
> > > the
> > > > > assumption that nested field syntax will be hardcoded or opt-in,
> > which
> > > > IIUC
> > > > > isn't the case anymore.
> > > > >
> > > > > 4. Nit: The "These SMTs do not require nested structure support"
> > > section
> > > > > mentions a "Drop" SMT. I think this may be referring to the
> Confluent
> > > > Drop
> > > > > SMT, which isn't a part of Apache Kafka. Should we drop (heh) that
> > SMT
> > > > from
> > > > > the list? Or perhaps just replace it with "DropHeaders", which is
> > > > currently
> > > > > missing from the list and shouldn't require any nested-field
> related
> > > > > updates?
> > > > >
> > > >
> > > > > Cheers,
> > > > >
> > > > > Chris
> > > > >
> > > > > On Mon, Feb 28, 2022 at 2:12 PM Jorge Esteban Quilcate Otoya <
> > > > > quilcate.jo...@gmail.com> wrote:
> > > > >
> > > > > > Thank you, Chris! and sorry for the delayed response.
> > > > > >
> > > > > > Please, find my comments below:
> > > > > >
> > > > > > On Mon, 14 Feb 2022 at 17:34, Chris Egerton
> > > > <chr...@confluent.io.invalid
> > > > > >
> > > > > > wrote:
> > > > > >
> > > > > > > Hi Jorge,
> > > > > > >
> > > > > > > Thanks for the KIP! I'd love to see support for nested fields
> > added
> > > > to
> > > > > > the
> > > > > > > out-of-the-box SMTs provided with Connect. Here are my initial
> > > > > thoughts:
> > > > > > >
> > > > > > > 1. I agree that there's a case to be made for expanding
> > HoistField
> > > > > with a
> > > > > > > new config property for identifying a nested, to-be-hoisted
> > field,
> > > > but
> > > > > > the
> > > > > > > example in the KIP doesn't really demonstrate why this would be
> > > > > > valuable. I
> > > > > > > think it'd be helpful to expand the example to add other fields
> > in
> > > > > order
> > > > > > to
> > > > > > > show how adding nested field support enables users to hoist a
> > > nested
> > > > > > field
> > > > > > > without dropping other fields from the value. Maybe something
> > like
> > > > > this:
> > > > > > >
> > > > > > > source = nested.val
> > > > > > > field = line
> > > > > > >
> > > > > > > value (before):
> > > > > > > {
> > > > > > > "nested": {
> > > > > > > "val": 42,
> > > > > > > "other val": 96
> > > > > > > }
> > > > > > > }
> > > > > > >
> > > > > > > value (after):
> > > > > > > {
> > > > > > > "nested": {
> > > > > > > "line": {
> > > > > > > "val": 42,
> > > > > > > }
> > > > > > > "other val": 96
> > > > > > > }
> > > > > > > }
> > > > > > >
> > > > > > > 2. Nit: I think "source" is a little strange for the new
> > HoistField
> > > > > > > property name. Maybe "hoisted" or "hoisted.field" would be more
> > > > > > > descriptive?
> > > > > > >
> > > > > > >
> > > > > > About 1. and 2.:
> > > > > > Agree. The example for this SMT is updated and have added the
> > > `hoisted`
> > > > > > configuration.
> > > > > >
> > > > > >
> > > > > > > 3. Is there a reasonable use case for expanding Flatten to be
> > able
> > > to
> > > > > > > flatten specific fields? My understanding is that it's mostly
> > > useful
> > > > > for
> > > > > > > writing to systems like databases that don't support nested
> > values
> > > > and
> > > > > > > require everything to be a flat list of key-value pairs. Being
> > able
> > > > to
> > > > > > > flatten a nested field wouldn't provide any advantage for that
> > use
> > > > > case.
> > > > > > > Are there other cases where it would?
> > > > > > >
> > > > > > > 4. I don't think we should unconditionally change the default
> > > > delimiter
> > > > > > for
> > > > > > > Flatten. It's a backwards-incompatible, breaking change that
> > could
> > > > > cause
> > > > > > > headaches for users. It might be reasonable to change the
> default
> > > > value
> > > > > > > dynamically based on whether the user has specified a value for
> > the
> > > > > > "field"
> > > > > > > property, but considering the motivation for changing the
> default
> > > is
> > > > > that
> > > > > > > it creates conflicts with the to-be-introduced nested field
> > syntax
> > > > > (which
> > > > > > > could arise with downstream SMTs regardless of whether the user
> > has
> > > > > > > explicitly configured Flatten with the "field" property), I
> don't
> > > > know
> > > > > > that
> > > > > > > this would be too useful either. I have some thoughts below on
> > how
> > > to
> > > > > > > handle possible conflicts between names with dots in their
> names
> > > and
> > > > > > dotted
> > > > > > > syntax for nested field references that should hopefully make
> > > either
> > > > > > change
> > > > > > > unnecessary.
> > > > > > >
> > > > > > >
> > > > > > Fair enough. With the support for nested fields in other SMTs,
> > > Flatten
> > > > > > could stay as it is.
> > > > > > This removes the need for (4) changing Flatten config as well.
> > > > > >
> > > > > >
> > > > > > > 5. I think it's fine to expand ExtractField to support nested
> > > > notation,
> > > > > > but
> > > > > > > it might be worth noting in the rejected alternatives section
> > that
> > > > this
> > > > > > > isn't strictly necessary since you can replace any single
> > > invocation
> > > > of
> > > > > > > that SMT that uses nested field notation with multiple
> > invocations
> > > of
> > > > > it
> > > > > > > that use non-nested notation.
> > > > > > >
> > > > > >
> > > > > > Agree. Adding it.
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > 6. Nit: "RegerRouter" should be "RegexRouter" in the list of
> SMTs
> > > > that
> > > > > do
> > > > > > > not require nested structure support.
> > > > > > >
> > > > > > >
> > > > > > Ack. Fixing it.
> > > > > >
> > > > > >
> > > > > > > 7. It may be rare for dots in field names to occur in the wild
> > > > > (although
> > > > > > I
> > > > > > > wouldn't be so certain of this), but unless we want to inflict
> > > > > headaches
> > > > > > on
> > > > > > > users of Flatten, I think we're going to have to think about
> > > > conflicts
> > > > > > > between dotted notation and non-nested fields whose names
> contain
> > > > > dots. I
> > > > > > > don't think this is actually such a bad thing, though. I agree
> > that
> > > > > > dotted
> > > > > > > notation is intuitive and pretty commonplace (in tools like jq,
> > for
> > > > > > > example), so I'd like it if we could stick to it. What about
> > > > > introducing
> > > > > > > escape syntax, using a backslash? That way, users could
> > > disambiguate
> > > > > > > between "this.field" (which would refer to the nested field
> > "field"
> > > > > under
> > > > > > > the top-level "this" field), and "this\.field" (which would
> refer
> > > to
> > > > > the
> > > > > > > field named "this.field"). Like with most languages that use
> the
> > > > > > backslash
> > > > > > > for escape sequences, it could also be used to escape itself,
> in
> > > the
> > > > > > event
> > > > > > > that a field name contains a backslash. I think this is more
> > > > intuitive
> > > > > > and
> > > > > > > simpler than, e.g., adding a new config property to toggle the
> > > > > delimiter
> > > > > > to
> > > > > > > be used when parsing nested field references.
> > > > > > >
> > > > > >
> > > > > > I like this approach. Adding to the KIP.
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > 8. I don't think we can unconditionally turn this feature on.
> The
> > > > risk
> > > > > of
> > > > > > > breaking existing pipelines (especially ones that involve, for
> > > > > example, a
> > > > > > > combination of the Flatten and Cast SMTs) is pretty high. I
> think
> > > > this
> > > > > > > should be an opt-in feature, at least until the next major
> > release.
> > > > One
> > > > > > way
> > > > > > > we could accomplish this is by introducing a new "field.style"
> > > (name
> > > > > > > obviously subject to change) property with values of "plain"
> > > > (default)
> > > > > > and
> > > > > > > "nested". If set to "plain" then the current non-nested
> behavior
> > is
> > > > > used,
> > > > > > > and if set to "nested", then the proposed nested behavior is.
> We
> > > can
> > > > > > > consider updating the default value to "nested" in a future
> major
> > > > > release
> > > > > > > (or even codify that plan in this KIP, if there's enough
> support
> > > for
> > > > > it).
> > > > > > > This would also leave the door open for adding recursive
> support
> > to
> > > > > SMTs
> > > > > > in
> > > > > > > the future by adding a permitted value of "recursive".
> > > > > > >
> > > > > > > 9. One of the linked tickets in the "Motivation" section,
> > > > > > > https://issues.apache.org/jira/browse/KAFKA-10640, has an open
> > PR
> > > > and
> > > > > > KIP
> > > > > > > that propose adding recursive support to some SMTs. Have you
> > > > considered
> > > > > > > this type of functionality for your KIP? Or is your aim to
> stick
> > > > solely
> > > > > > to
> > > > > > > nested field support?
> > > > > > >
> > > > > >
> > > > > > I like the `field.style` configuration flag approach.
> > > > > > Thanks for pointing out the `recursive` approach. Will add
> `nested`
> > > at
> > > > > the
> > > > > > moment, let's check the demand for `recursive` to consider it as
> > part
> > > > of
> > > > > > this or another KIP.
> > > > > >
> > > > > > I have added the following on the KIP:
> > > > > >
> > > > > > ```
> > > > > > Future KIPs could extend this support for:
> > > > > >
> > > > > > - Recursive notation: name a field and apply it to all fields
> > across
> > > > the
> > > > > > schema matching that name.
> > > > > > - Access to arrays: Adding `[]` notation to represent access to
> > > arrays
> > > > > and
> > > > > > applying SMTs to fields within an array.
> > > > > > ```
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > Cheers,
> > > > > > >
> > > > > > > Chris
> > > > > > >
> > > > > > > On Tue, Feb 8, 2022 at 1:23 PM Jorge Esteban Quilcate Otoya <
> > > > > > > quilcate.jo...@gmail.com> wrote:
> > > > > > >
> > > > > > > > Hi Dev team,
> > > > > > > >
> > > > > > > > I'd like to start a new discussion thread on Kafka Connect
> > > KIP-821:
> > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> https://cwiki.apache.org/confluence/display/KAFKA/KIP-821%3A+Connect+Transforms+support+for+nested+structures
> > > > > > > >
> > > > > > > > This KIP is aimed to include support for nested structures on
> > the
> > > > > > > existing
> > > > > > > > SMTs — where this make sense.
> > > > > > > >
> > > > > > > > Looking forward to your feedback.
> > > > > > > >
> > > > > > > > Regards,
> > > > > > > > Jorge.
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>
