kandi X-RAY | flink-cep Summary
kandi X-RAY | flink-cep Summary
Top functions reviewed by kandi - BETA
- Entry point for testing
- Gets the value type
flink-cep Key Features
flink-cep Examples and Code Snippets
Trending Discussions on flink-cep
I'm trying to use Flink to consume a bounded data from a message queue in a streaming passion. The data will be in the following format:...
ANSWERAnswered 2021-Nov-04 at 08:56
There are a couple of things getting in the way of what you want:
(1) Flink's window operators produce append streams, rather than update streams. They're not designed to update previously emitted results. CEP also doesn't produce update streams.
(2) Flink's file system abstraction does not support overwriting files. This is because object stores, like S3, don't support this operation very well.
I think your options are:
(1) Rework your job so that it produces an update (changelog) stream. You can do this with toChangelogStream, or by using Table/SQL operations that create update streams, such as
GROUP BY (when it's used without a time window). On top of this, you'll need to choose a sink that supports retractions/updates, such as a database.
(2) Stick to producing an append stream and use something like the
FileSink to write the results to a series of rolling files. Then do some scripting outside of Flink to get what you want out of this.
In this project, I'm trying to consume data from a Kafka topic using Flink and then process the stream to detect a pattern using Flink CEP. The part of using Kafka connect works and data is being fetched, but the CEP part doesn't work for some reason. I'm using scala in this project.
ANSWERAnswered 2021-Apr-12 at 11:46
pattern.get("first") you are selecting a pattern named "first" from the pattern sequence, but the pattern sequence only has one pattern, which is named "start". Trying changing "first" to "start".
Also, CEP has to be able to sort the stream into temporal order in order to do pattern matching. You should define a watermark strategy. For processing time semantics you can use
I am newbie to Flink i am trying a POC in which if no event is received in x amount of time greater than time specified in within time period in CEP...
ANSWERAnswered 2020-Oct-17 at 20:26
Your application is using event time, so you will need to arrange for a sufficiently large Watermark to be generated despite the lack of incoming events. You could use this example if you want to artificially advance the current watermark when the source is idle.
Given that your events don't have event-time timestamps, why don't you simply use processing time instead, and thereby avoid this problem? (Note, however, the limitation mentioned in https://stackoverflow.com/a/50357721/2000823).
first of all I have read this post about the same issue and tried to follow the same solution that works for him (create a new quickstart with mvn and migrate the code there) and is not working eighter when out-of-the-box of IntelliJ.
Here is my pom.xml mixed with my dependencies from the other pom.xml. What am I doing wrong?...
ANSWERAnswered 2020-Aug-27 at 06:54
The error appears when
flink-clients is not in the classpath. Can you double-check if your profile is working as expected by inspecting the actual classpath? Btw for IntelliJ you don't need the profile at all. Just tick the option to include provided dependencies in the Run/Debug dialog.
Running Flink 1.9.0 with Scala 2.12 and attempting to publish data to Kafka using the
flink-connector-kafka, everything works fine when debugging locally. Once I submit the job to the cluster, I get the following
java.lang.LinkageError at runtime which fails to run the job:
ANSWERAnswered 2020-Aug-24 at 11:04
For an unknown reason, setting the
classloader.resolve-order property to
parent-first as mentioned in the Apache Flink mailing list resolves the issue. I am still baffled as to why it works, as there should be no dependency clashes between the child and parent classloader loading different versions of this dependency (as it is not provided out of the box with the
flink-dist I am using).
In the Flink documentation under "Debugging Classloading", there's a section which talks about this parent-child relationship:
In setups where dynamic classloading is involved (plugin components, Flink jobs in session setups), there is a hierarchy of typically two ClassLoaders: (1) Java’s application classloader, which has all classes in the classpath, and (2) the dynamic plugin/user code classloader. for loading classes from the plugin or the user-code jar(s). The dynamic ClassLoader has the application classloader as its parent.
By default, Flink inverts classloading order, meaning it looks into the dynamic classloader first, and only looks into the parent (application classloader) if the class is not part of the dynamically loaded code.
The benefit of inverted classloading is that plugins and jobs can use different library versions than Flink’s core itself, which is very useful when the different versions of the libraries are not compatible. The mechanism helps to avoid the common dependency conflict errors like IllegalAccessError or NoSuchMethodError. Different parts of the code simply have separate copies of the classes (Flink’s core or one of its dependencies can use a different copy than the user code or plugin code). In most cases, this works well and no additional configuration from the user is needed.
I have yet to understand why loading
ProducerRecord happens more than once, or what this "different type" in the exception message refers to (greping on the result of
-verbose:class yielded only a single path for
I started studying Apache Flink's CEP libraries in Scala language, and as I was trying to create a PatternStream by executing
CEP.pattern(input,pattern) as shown in the tutorial at https://ci.apache.org/projects/flink/flink-docs-stable/dev/libs/cep.html, the IDE says that it "Cannot resolve overloaded method", referring to the
pattern method. According to the implementation of
Pattern[String].begin('line').where(_.length == 10), both of which I used to create the input and pattern respectively, there shouldn't be any problems with the method's arguments or generic types.
Here goes the code I wrote. I know it isn't complete, but I couldn't complete it anyways since this problem came up....
ANSWERAnswered 2020-Jan-14 at 08:41
No vulnerabilities reported
You can use flink-cep like any standard Java library. Please include the the jar files in your classpath. You can also use any IDE and you can run and debug the flink-cep component as you would do with any other Java program. Best practice is to use a build tool that supports dependency management such as Maven or Gradle. For Maven installation, please refer maven.apache.org. For Gradle installation, please refer gradle.org .
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