heapdump-analyser

heapdump-analyser dump.heapsnapshot

Enters interactive mode.

heapdump-analyser dump.heapsnapshot ClassToFind
heapdump-analyser dump.heapsnapshot ClosureToFind()
heapdump-analyser dump.heapsnapshot @IdToFind

Finds all ClassToFind classes or ClosureToFind closures in the heapsnapshot and prints out a colorful retainer trace for them.

heapdump-analyser a.heapsnapshot b.heapsnapshot c.heapsnapshot [ClassToFind|ClosureToFind()|@IdToFind]

Finds only retained objects in c.heapsnapshot that were allocated between a.heapsnapshot and b.heapsnapshot.

Compared to the v8 devtools it

• correctly analyses WeakMaps and circular dependencies within them.
• eliminates references between the classes/closures you are looking for.

Note that it may take a large amount of memory for the analysis so you may want to increase the max memory with NODE_OPTIONS=--max_old_space_size=16000. It takes about 16x size of heapsnapshot.

Creating a heapsnapshot

Note that creating a heapsnapshot is pretty slow and blocks execution of your code.

Node.js CLI

Since Node.js 16 you can use --heapsnapshot-near-heap-limit=1 to create a heapsnapshot when the process runs out of memory. Best reduce the available amount of memory via --max_old_space_size=500 to make it run out of memory faster and make the size of the heapsnapshot smaller.

node --max_old_space_size=500 --heapsnapshot-near-heap-limit=1 program.js

It also possible to create a heapsnapshot on a signal via --heapsnapshot-signal=SIGUSR2

node --heapsnapshot-signal=SIGUSR2 program.js

ps aux
kill -USR2 1234

heapdump package

The npm package heapdump allows to create a heapsnapshot from javascript:

console.log("creating heapdump...");
require("heapdump").writeSnapshot((err) => console.log("done", err));

Node.js devtools

Using the devtools is not recommended since the devtools affect the results, are very slow and crash when the heapsnapshot is too large.