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How to Improve Problem Solving Skills - Developer Guide

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How to Improve Problem Solving Skills

Jeffery Yuan

April 24, 2019

Why Problem-solving skills matters

Problem Solving and troubleshooting

Is fun

Is part of daily work

Solve the problem, get things done

Work More efficiently

With more confidence

Less pressure

Go home earlier

Solve the problem when needed

It’s your responsibility if it blocks you, the team

How to Solve a Problem

Understand the problem/environment first

Understand the problem before google search otherwise it may just lead you to totally wrong directions.

Find related log/data

Copy/Save logs/info/findings that may be related

Check the Log and Error Message

Read/Understand the error message

Where to find log

Common places: /var/log

From command line:

-Dcassandra.logdir=/var/log/cassandra

Case Study – The Log and Error Message

Problem: Failed to talk Cassandra server: 10.10.10.10

Where 10.10.10.10 comes from?

gfind . -iname '*.jar' -printf "unzip -c %p | grep -q 10.10.10.10' && echo %p\n"

or search in corporate github/code base

It comes from commons2 project; check what’s the current settings in Github

Now the problem and solution is clear

Just upgrade commons2 to latest version

Source code is always the ultimate truth

Find related code in Github

Find examples/working code

Understand how/why the code works by running and debug the code

Check the log with the code

Most problems can be solved by checking log and source code

Reproduce the problem

Find easier way to reproduce them

main method, unit test, mock

Simplify the suspect code

Find the code related, remove things not realtedUse

Reproduce locally

Connect to the remote data in local dev

Remote debug

Last resort, slow

Solving Problem from Different Angles

Sometime we find problem in production and we need code change to fix it

Try to find a workaround by changing database/Solr or other configuration

We can fix code later

Find Information Effectively

Google search: error message, exception

Search source code in Github/Eclipse

Search log

Search in IDE

Cmd+alt+h, cmd+h

Search command history

history | grep git | grep erase

history | grep ssh | grep 9042

history | grep kubectl | awk ‘{$1="";print}’ | sort -u

Find Information Effectively Cont.

Know company’s internal resource

where to find them

Know some experts (in company) you can ask help from

How to Troubleshoot and Debug

Don’t overcomplicate it.

In most cases, the solution/problem is quite simple

Troubleshooting is about thinking what may go wrong.

Track what change you have made

Resource About Troubleshooting

Debug It!: Find, Repair, and Prevent Bugs in Your Code

Urgent Issues in Production

Collaborate and share update timely

Let others know what you are testing/checking, the progress, what you have found, what you will do next

Ask for help

Before

Try to understand the problem and fix it by yourself first

If this applies: not urgent

Where and Who

Coworkers

Involve more people: the team, related teams

Stackoverflow

Specific forums

http://bit.ly/2QHXwq4

Google Groups

Github issues

Ask in multiple channels

How to Ask Help

Provide more context and info

log, stack trace or any information that may help others understand the problem

Provide what you have found, tried

Ask help once for same/similar/related issues

Learn more

The knowledge: root cause, etc

Learn their thinking process

how they approach this problem (logs, code), tools

Fix same/similar/related problems in other places

People make same mistakes in different places

Example: GetMapping(value = "/config/{name:.+}")

Knowledge

Be prepared

Learn how to debug/troubleshooting

Learn tools used for debugging

Learn framework, library, products, services used in your project

Apache/Tomcat configuration

How to manage/troubleshoot Cassandra/Kafka/Solr

Know what problem may happen, code change recently

Knowledge cont.

Common Problems

Different versions of same library

mvn dependency:tree

mvn dependency:tree -Dverbose -Dincludes=com.amazonaws:aws-java-sdk-core

Tools

Tools - Eclipse

Use Conditional Breakpoint to Execute Arbitrary Code (and automatically)

Use Display View to Execute Arbitrary Code

Find which jar containing the class and the application is using

MediaType.class.getProtectionDomain().getCodeSource().getLocation()

Breakpoint doesn’t work

Multiple versions of same class or library

Practice - Connect to the remote data in local dev

Create a tunnel to zookeeper and solr nodes

Add a conditional breakpoint at CloudSolrClient.sendRequest(SolrRequest, String)

before LBHttpSolrClient.Req req = new LBHttpSolrClient.Req(request, theUrlList);

theUrlList.clear(); theUrlList.add("http://localhost:18983/solr/searchItems/"); theUrlList.add("http://localhost:28983/solr/searchItems/"); return false;

Tools - Decompiler

GUI: Bytecode-Viewer

alias decom=“java -jar /Users/jyuan/apple/tools/misc/Bytecode-Viewer-2.9.11.jar”

CFR

Best, Support java8

Tools - Java

jcmd: One JDK Command-Line Tool to Rule Them All

jcmd Thread.print

jcmd GC.heap_dump

Thread dump Analyzer

http://fastthread.io/

Heap dump Analyzer

Eclipse MAT

VisualVM

Tools - Splunk

Syntax

Expand messages to show all fields

Click Format on the top and select All lines for the Max Lines setting

After search and find the problem, use nearby Events +/- x seconds to show context

Tools - Misc

Search Contents of .jar Files for Specific String gfind . -iname '*.jar' -printf "unzip -c %p | grep -q 'string_to_search' && echo %p\n" | s

nc -zv, lsof, df, find, grep

Fiddler

Problem Solving in Practice

Example: Redis cache.put Hangs

Get thread dump, figure out what’s happening when read from cache

Read related code to figure out how Spring implements @Cacheable(sync=true) RedisCache$RedisCachePutCallback

Check whether there’s cacheName~lock in redis

When use some feature, know how it’s implemented.

Practice - Iterator vs Iterable

What’s the problem in the following Code?

@Cacheable(key = "#appName") public Iterator<Message> findActiveMessages(final String appName) {}

Practice - Iterator vs Iterable

How to find the root cause

Symptoms: The function only works once in a while: when cache is refreshed

Difference between Iterator vs Iterable

Don’t use Iterator when need traverse multiple times

Don’t use Iterator as cache value

Practice 2 - Spring Cacheable Not Working

The class using cache annotation inited too early

Add a breakpoint at the default constructor of the bean, then from the stack trace we can figure out why and which bean (or configuration class) causes this bean to be created

Understand how spring cache works internally, spring proxy

CacheAspectSupport

Post Mortem

Reflection: Lesson Learned

How we find the root causeWhy it takes so long

What we have learned

What’s the root cause

Why we made the mistake

How we can prevent this happens again

Share the knowledge in the team via wiki, quip, email etc.

Take time to solve problem, find the root cause, but only (take time to) solve it once

Think More

Think over the code/problem, try to find better solution even the issue’s solved

Everything that stops you from working effectively is a problem

Fix them

Bonus

Building Troubleshooting-Friendly Application

Return meaningful error code and response

Return debug info that can check from response when requested

Should be safe to use or protected

Add requested_id in client (automatically when provide client application)

Mock User Feature

Preview Feature

How to write test efficiently

Learn and Use Hamcrest, Mockito, JUnit, TestNG, REST Assured

Add Static Import in Eclipse

Preferences > Java > Editor > Content Assist > Favorites, then add:

org.hamcrest org.hamcrest.Matchers.* org.hamcrest.CoreMatchers.* org.junit.* org.junit.Assert.* org.junit.Assume.* org.junit.matchers.JUnitMatchers.* org.mockito.Mockito org.mockito.Matchers org.mockito.ArgumentMatchers io.restassured.RestAssured

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