V8 Compile Cache

[rauchg]

The idea is that we can emit not just .js files, but also the v8 code cache blobs.
And unlike v8-compile-cache, we could benefit from making all bootups fast, including the first one. Also unlike it, we can use the new createCachedData APIs which have some benefits.

• Make sure we disable the optimization gracefully when invoking in old Node versions
• Make sure to add a flag to disable it (--no-v8-cache)

More:

• vm: add Script.createCodeCache() nodejs/node#20300
• nodejs/node@4f67c6f
• Adopt createCachedData when possible microsoft/vscode#62643
• https://nodejs.org/dist/latest-v10.x/docs/api/vm.html#vm_script_createcacheddata
• (legacy) https://nodejs.org/api/vm.html#vm_new_vm_script_code_options produceCachedData
• (legacy) https://www.npmjs.com/package/v8-compile-cache

[rauchg]

It'd be neat to self-host this as well. Right now ncc takes 350ms~ to boot up, and the TypeScript compiler adds another 350ms~.

[guybedford]

I just ran a simple test of the following code:

create-cache.js

const fs = require('fs');
const { Script } = require('vm');
const script = new Script(fs.readFileSync('./index.js').toString());
fs.writeFileSync('./index-cache', script.createCachedData());

index-cached.js

const fs = require('fs');
const source = fs.readFileSync('./index.js').toString();
const cachedData = fs.readFileSync('./index-cache');
const fs = require('fs');
const { Script } = require('vm');
const source = fs.readFileSync('./index.js').toString();
const cachedData = fs.readFileSync('./index-cache');
var s = new Script(source, { cachedData });
s.runInNewContext({
  module,
  exports,
  require,
  process,
  Buffer,
  console,
  global
});

where we then compare running time node index-cached.js and time node index.js.

Here are the results:

• Analytics-node: 137ms uncached, 130ms cached
• Twilio: 400ms uncached, 280ms cached
• Canvas: 145ms uncached, 145ms cached

So it seems the benefit only really applies for very large builds... but it does seem like there is a benefit there in some cases, which may be enough to justify it as a custom flag.

I can basically replicate the above as a flag option... will do a PR now.

[simlu]

We're getting a TypeError: (intermediate value).createCachedData is not a function.

Is anyone still using this or has an idea what is going on?

Edit: This is potentially a problem with the node version (we are using node 8.10 since that is used on AWS Lambda). When running it with v10.15.3 we get a Error: ENOENT: no such file or directory, open '/tmp/tmp-83405GC5OuSR09SSO/index.js.cache.js' (which is our temporary test directory).

[simlu]

I'm guessing this doesn't work when executing programmatically?

[guybedford]

@simlu are you explicitly using the --v8-cache flag here with an ncc build workflow? Yes it would not be supported in Node 8 though, as this is a recent v8 feature.

[sourcevault]

how big has the build has to be useful ? 0.5 MB, 2 MB ? 100 MB ?