Hi Tom, hi Chris, in principle an expression language sounds good, as it would allow us to cover pretty much any use-case that we could possibly come up with. And bearing in mind that I was the one who originally started talking about more complex use-cases, I should be happy about that :)
That being said, I have my doubts, whether we'd be doing the world a favor by heading down this road. There are or have been quite a few data transformation DSLs out there, there is Camel's simple [1], Cloudera had a try with Morphlines (or later KiteSDK) [2], Heka [3] and Logstash [4] both allow defining transformation pipelines - and those are just the ones I came up with of the top of my head. Instead of trying to evolve SMTs into the direction these tools have taken, maybe there is worth in keeping these transforms simple and limited and if more complex processing is needed pick something that is better suited - Kafka Streams would definitely be an option as well for example. I hope that makes sense? Happy to elaborate more if this just reads like gibberish :) Best regards, Sönke [1] https://livebook.manning.com/book/camel-in-action-second-edition/appendix-a/1 [2] https://blog.cloudera.com/introducing-morphlines-the-easy-way-to-build-and-integrate-etl-apps-for-hadoop/ [3] https://hekad.readthedocs.io/en/v0.10.0/ [4] https://www.elastic.co/guide/en/logstash/current/pipeline.html On Thu, 2 Apr 2020 at 18:48, Tom Bentley <tbent...@redhat.com> wrote: > 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 > > > > > > > > > > > > > > > > -- Sönke Liebau Partner Tel. +49 179 7940878 OpenCore GmbH & Co. KG - Thomas-Mann-Straße 8 - 22880 Wedel - Germany
