[GitHub] [spark-website] sririshindra commented on a change in pull request #280: Add documentation for debugging with Maven and IntelliJ.

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sririshindra commented on a change in pull request #280:
URL: https://github.com/apache/spark-website/pull/280#discussion_r453796365



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File path: developer-tools.md
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@@ -435,6 +435,44 @@ Error:(147, 9) value q is not a member of StringContext
         q"""
         ^ 
 ```
+
+<h4>Debugging Spark unit tests with Intellj and Maven</h4>
+This part will show how to debug spark locally with maven.
+
+- Once the spark project in imported as a maven project install spark using the following command.
+    ```
+    $ ./build/mvn -DskipTests clean install
+    ``` 
+    Then open the maven tab in Intellij(usually present in the top right corner) and reload all maven projects.
+    Now, open any unit test and right click on the play button for debugging options. A good way to test 
+    your changes or understand some part of the code is to write a dummy unit test, add a few breakpoints
+    to the part of the code that you are interested in and run the debugger. You could right click on a test Suite
+    and debug/run all tests in that Suite
+
+- To keep your development spark from polluting your .m2 cache you can specify a custom maven repository location
+during install.
+    ```
+    $ ./build/mvn -DskipTests clean install -Dmaven.repo.local=/Users/dummyuser/repos/Jiras/SPARK-xyz/.m2
+    ```
+    Accordingly Intellij has to be configured to point to this custom location of m2 cache. To do this
+
+    Go to Preferences> search for maven > Local Repository > Click the override button> update the new location 
+
+-  It is sometimes necessary to stop only a specific thread at a break point. For example, you might want to see the 
+Spark UI at particular break point during your debugging session. In that case right click on the break point and select
+"Thread" option. This will cause the execution in the current thread to pause and will let the other threads continue.   
+
+- When running unit tests for the whole project or a module you might run something like this in a terminal
+    ```
+    $ ./build/mvn -pl sql/hive clean test
+    ``` 
+    You can run the same in Intellij instead of terminal. 
+    Go to Maven Tab > Click on the 'm'(execute maven goal) icon and paste your maven command.
+    The advantage of running there maven command here instead of the terminal is that you get a clickable stacktrace 
+    when there are test failures. This helps in navigating the code easily. You might want to increase the size limit
+    of your console output so that the logs will not be swallowed. Typically, setting it to 10MB is good enough. 

Review comment:
       Yes, you are right. This is more of a side note. We could run and a specific unit test or an entire Suite directly in Intellij.
   But, I haven't been able to figure out to how to run all the tests in a module with in Intellij directly. When I right click on module and run All Scala tests, Intellij eventually fails with something like the following exception. 
   
   `Unable to load a Suite class. This could be due to an error in your runpath. Missing class: org.apache.spark.unsafe.types.UTF8StringPropertyCheckSuite
   java.lang.ClassNotFoundException: org.apache.spark.unsafe.types.UTF8StringPropertyCheckSuite`
   
   Clicking on the test goal in the maven lifecycle of a module runs the module and fails with something like the following.
   `Failed to execute goal org.scalatest:scalatest-maven-plugin:2.0.0:test (test) on project spark-hive_2.12: There are test failures`
   Even when there are no test failures. It says that there are some test failures. 
   
   My guess is that there is something wrong with the configuration in both cases and I haven't figured out a way to fix it.
   
   The only work around that I can come up with is use the above technique. I can remove it if you think, this is trivial.




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