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dart-sdk/runtime/docs/snapshot_profiling.md
Samir Jindel 526b11d28e [vm] Add doc for snapshot profiling. 
Change-Id: Ib33dffd5d7ad4bb6c3fc9eb83a8b321b6a85495c
Reviewed-on: https://dart-review.googlesource.com/c/86024
Auto-Submit: Samir Jindel <sjindel@google.com>
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
2018-12-12 12:38:13 +00:00

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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 ".heapsnaphsot" 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 https://developers.google.com/web/tools/chrome-devtools/memory-problems/heap-snapshots 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.