@rocicorp/heap-snapshot

It is often the case that we need to get a heap snapshot from running zero-cache processes.

Online guides and documentation suggest using the chrome-remote-interface package and then calling v8.writeHeapSnapshot().

Doing this for zero-cache yields much smaller snapshots than those you get if you connect to the node process in Chrome's devtools and get a snapshot that way. These smaller snapshots lack many core classes of zero-cache such as ViewSyncer.

I do not understand why but ChatGPT suggests that the implementation of v8.writeHeapSnapshot() is different and simpler than the HeapProfiler class that Chrome itself uses, and misses some "uncommon" allocation patterns 😬.

This tool automates using the lower-level HeapProfiler class to create a dump that contains all of zero-cache's objects.

Usage

1. kill -USR1 <pid-to-snapshot>
2. The targetted process prints out a message like: Debugger listening on ws://127.0.0.1:9229/a8712980-d35d-434f-824c-db212b277b5e
3. npx @rocicorp/heap-snapshot <that-url>