If you'd like to contribute a patch to Impala, but aren't sure what you want to work on, you can look at Impala's newbie issues: https://issues.apache.org/jira/issues/?filter=12341668. You can find detailed instructions on submitting patches at https://cwiki.apache.org/confluence/display/IMPALA/Contributing+to+Impala. This is a walkthrough of a ticket a new contributor could take on, with hopefully enough detail to get you going but not so much to take away the fun.
How can we fix https://issues.apache.org/jira/browse/IMPALA-5392, "Stack depth for threads printed in the Catalog UI under JVM Threads is not deep enough"? First, set up your development environment and start a development impala cluster by running bin/start-impala-cluster.py. Once it is running, check out http://localhost:25020/jvm-threadz, which you will see referenced offhand in http://impala.apache.org/docs/build/html/topics/impala_webui.html. That page has the stack traces the ticket (IMPALA-5392) is talking about. You can see that several end in ellipses, indicating they are cut off. Fixing that is the aim of this ticket. In www/jvm-threadz.tmpl, you will see the template for creating this page. The section to fix is "{{summary}}". To see where this is populated, git grep jvm-threadz. There you will see it is referenced in be/src/util/thread.cc. The references to summary in that file are getting that information from a TJvmThreadInfo object, so we'll need to trace where the summary field of that object is populated. That object is referenced in common/thrift/Frontend.thrift, which is its definition, and in fe/src/main/java/org/apache/impala/common/JniUtil.java. In that file, you will see setSummary called with the result of a call to java.lang.management.ThreadInfo.toString(), which is described here: https://docs.oracle.com/javase/8/docs/api/java/lang/management/ThreadInfo.html#toString-- Investigate those docs and find a way to add more stack trace information. Once you think you have it, you will need to rebuild and restart the cluster: ./buildall.sh -notests -noclean -ninja -start_impala_cluster Reload the webpage and admire your handiwork! Once you're satisfied, submit your patch for review following the instructions on https://cwiki.apache.org/confluence/display/IMPALA/Contributing+to+Impala.
