Leak Hunting - Finding and debugging a memory leak in Nodejs.pdf

N O V E M B E R 2 3
, 2 0 1 8 C O N F I D E N T I A L Leak Hunting Finding and debugging a memory leak in Node.js

C O N F I D E N T I
A L © 2018 NodeSource Developers/Companies (not all) don’t consider how diﬀicult could be to track and fix a memory leak until it happens

C O N F I D E N T I
A L © 2018 NodeSource Developers/Companies (not all) don’t consider how diﬀicult could be to track and fix a memory leak until it happens … a day before the release date

C O N F I D E N T I
A L © 2018 NodeSource Developers/Companies (not all) don’t consider how diﬀicult could be to track and fix a memory leak until it happens … after a new cool feature is pushed

C O N F I D E N T I
A L © 2018 NodeSource Developers/Companies (not all) don’t consider how diﬀicult could be to track and fix a memory leak until it happens … in production on Friday night

C O N F I D E N T I
A L © 2018 NodeSource Developers/Companies (not all) don’t consider how diﬀicult could be to track and fix a memory leak until it happens … prod gets more client request than dev tests

© 2018 NodeSource C O N F I D E
N T I A L Quick brief around Memory in Node.js

N T I A L Garbage Collection Every program that consumes memory requires a mechanism for reserving and freeing space.

N T I A L How GC works: • Root R

N T I A L How GC works: • Root. • Object. R O O O O

N T I A L How GC works: • Root. • Object. • Primitives. R O O O O P P

N T I A L How GC works: • Root • Object. • Primitives. • Non referenced object. R O O O O P P O P

N T I A L Memory scheme (v8): • Resident Set R E S ID E N T SE T

N T I A L Memory scheme (v8): • Resident Set • Code Segment R E S ID E N T SE T CO DE S E GM E NT

N T I A L Memory scheme (v8): • Resident Set • Code Segment • Stack R E S ID E N T SE T CO DE S E GM E NT STACK

N T I A L Memory scheme (v8): • Resident Set • Code Segment • Stack • Heap R E S ID E N T SE T CO DE S E GM E NT STACK H E AP

N T I A L Memory scheme (v8): • Resident Set • Code Segment • Stack • Heap • Used heap R E S ID E N T SE T CO DE S E GM E NT STACK H E AP RSS   H E APTOTA L   H E AP US E D  E XT E R N AL

N T I A L Relation between GC and a memory leak? • Impossible to remove non referenced data. • Portion of memory allocated not released when no longer needed.

N T I A L Memory Leak causes: • Registered event handlers • Function closures • Leaking connections

N T I A L Types of production issues

N T I A L 1. Runtime performance: • The website/app is slow. • Not giving a great/fast experience to the user.

N T I A L Things you can do on Runtime performance issues: • --perf-basic-prof-only-functions. • A system tool like Perf Events in Linux. • Spare the traces that are really important in your situation.

N T I A L 2. Runtime crashes: • Uptime is critical. • Not easily to reproduce. • Resume the process asap.

N T I A L Things you can do on Runtime crashes: • --abort-on-uncaught-exception. • Use some system tooling llbd, gbd, mdb.

N T I A L 3. Memory leaks: • This will be our focus today.

N T I A L Let’s do it!

N T I A L 27 Process to investigate an issue: • Think and construct an hypothesis • Collect data • Analyze the data (duh) • Draw a conclusion • Repeat (profit?)

N T I A L 28 Strategy for Memory Leaks detection: • Inspect objects for more context. • Look for weird objects on heap • Growing object counts are likely leaking • Walk reverse references to find the root object • Compare object counts !important

N T I A L Node.js Using V8 Inspector & Chrome Dev Tools • Run your node process with --inspect • Check chrome://inspect • Run it!

N T I A L Taking Snapshots of the V8 Memory • Check the Memory tab • Take heap snapshot • Profit!

N T I A L What is happening? • On the first snapshot, there are already/almost 7-8MB allocated before any request is processed. • Memory keeps growing while the server is running • Date and Objects have been allocated between the two load sessions.

N T I A L Possible solution: • Reduce Date • The solution for this example is to store the logs not in memory, but on the filesystem

N T I A L • As you can see, the memory growth is far slower! • This said, the API takes more time to respond. Reading and writing to the disk comes with a cost, so do other API calls or database requests.

N T I A L Do something before it happens 34

N T I A L Endurance Testing Primary goal of Endurance testing is to check for memory leaks.

N T I A L 36 Goals • Discover how the system performs under sustained usage • Ensure that after a long period, the system response time will remain the same or better than the start of the test. • Manage the future loads, we need to understand how many additional resources are necessary to support usage in future

N T I A L k6 is your friend • Can output more granular metrics than what is printed on stdout • Testing tool for testing the performance of   your backend infrastructure • Written in Go and JavaScript

N T I A L 38 N|Solid to the rescue! • Monitoring and diagnostic tools to help identify and tackle tricky issues. • Production friendly. • Shows performance insights. • Helps you build highly reliable applications and minimize infrastructure costs.

N T I A L Name you functions.. or not?

N T I A L • Var test = function () {}

N T I A L • Var test = function () {} • test.protory.biz = function () {}

N T I A L • Var test = function () {} • test.protory.biz = function () {} • fs.writeFile(chunck, function(err) {})

N T I A L • Var test = function () {} • test.protory.biz = function () {} • fs.writeFile(chunck, function(err) {}) • What about arrow functions?

N T I A L Don’t block on I/O

N T I A L I/O operations are… • Expensive. • A waste of resources if your program is unable to do other work. • Usually a hidden operation.

N T I A L Blocking the Event Loop • Totally possible • Happens more times we want it to happen (who wants to block it in first place?) • Iterations and complex calculations would prevent the process from handling other events

N T I A L Succeed doing I/O operations: • Choose asynchronous over synchronous • Opt for parallel I/O wherever possible • Don't hog the JavaScript thread with long-running calculations and iterations

N T I A L Async FTW! Modern applications spend most of their time waiting for I/O

N T I A L • Better work scheduling • Reduces thread CPU overhead • V8 can only do one thing at a time • Spend as little time in V8 as possible

N T I A L What we can learn from this: • Is never a good idea wait for Friday at night to learn about memory in Node.js

C O N F I D E N T I
A L Thank you. Giovanny Gongora [email protected] @Gioyik

Leak Hunting - Finding and debugging a memory l...

Leak Hunting - Finding and debugging a memory leak in Nodejs.pdf

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