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heap-profile

Sampling Heap Profiler

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EXPERIMENTAL

This module adds supports for the experimental Sampling Heap Profiler in V8. This works by taking a random sample of objects, as they are allocated, to keep a statistical sample of what is live in the heap at any given time. This also keeps track of the stack that allocated a given sampled object. This means that you know not only what is live, but what code path allocated it. This is motivated by, and functions similarly to, the heap profiler built into tcmalloc.

  • The generated snapshots can be opened in DevTools.
  • This is supposed to be lightweight enough for in-production use on servers.

Usage

const heapProfile = require('heap-profile');
 
heapProfile.start();
 
// Write a snapshot to disk every hour
setInterval(() => {
  heapProfile.write((err, filename) => {
    console.log(`heapProfile.write. err: ${err} filename: ${filename}`);
  });
}, 60 * 60 * 1000).unref();

start()

Starts sampling. You probably want to call this as close to the program startup as possible.

get()

Returns the profile composed of a tree of nodes.

write([filename], cb)

Writes the current heap sample to a file. If the filename parameter is omitted, a default pattern of heap-profile-${Date.now()}.heapprofile.

The callback returns error if profiling was not active at the time of call. Otherwise the name of the file is returned via the callback.

stop()

Stops sampling and discard the current set of tracked sampled objects. You can call start again to start sampling again, but any objects allocated before start is called cannot be sampled, which means that the profile will not be representative of the state of the heap.

The sampling overhead is low enough that you probably don't need to use stop.