AOT Snapshot Size Profiling

The VM supports profiling the size of AOT snapshots by leveraging the object-graph based file format introduced by V8.

Recording a profile

To generate a snapshot profile, simply pass the --write-v8-snapshot-profile-to=<filename> flag to gen_snapshot. The profile will be written in JSON format to the requested file. Make sure to use the “.heapsnapshot” extension for the file to open it in Chrome DevTools.

Examining a profile in Chrome

Open Chrome DevTools, navigate to the “Memory” tab, right-click on the “Profiles” panel, click Load..." and select the snapshot profile file. See for details on how to use the tool.

Examining a profile programmatically

A Dart library to parse the snapshot profile format is provided in pkg/vm/lib/v8_snaphsot_profile.dart. The dart2js_info package has some useful code for calculating retainers and other graph statistics.