Heap snapshot is missing ability to navigate around

[rmacnak-google]

Cannot look at an object and follow successors, predecessors, dominator parent, dominator children, etc.

[polina-c]

@rmacnak-google

Will memory analysis tool meet your goals:

% git clone https://dart.googlesource.com/sdk.git
% cd sdk/runtime/tools/heapsnapshot
sdk/runtime/tools/heapsnapshot % dart pub get
sdk/runtime/tools/heapsnapshot % dart bin/explore.dart
The Dart VM *.heapsnapshot analysis tool
Type `exit` or use Ctrl+D to exit.

(hsa) load <*.heapsnapshot>

See video demo at timestamp 3:28 of go/day-1:-dash-team-summit-cam

[polina-c]

cc @mkustermann

[polina-c]

We could reference the tool in DevTools for those who want to explore the snapshot.

[rmacnak-google]

No, the existence of the ability to navigate snapshots in tools/heapsnapshot, Graph Explorer and Observatory does not fix its absence in DevTools. The ability to just look at what's in the snapshot is the fundamental operation. Analysis is secondary.

[mkustermann]

There are close parallels between examining an application live and examining a snapshot of a live application state (which we use heap snapshots for).

In the ideal case I'd say that most/all debugger features we have (for a live application) could also be implemented for a snapshot of a live application state (a heapsnapshot). Inspecting an object is one such thing. The only? exception would be debugger features that require actually executing dart code.

While making the runtime/tools/heapsnapshot tool I have run into some limitations of the heap snapshot format that makes it difficult to build some of those features. I think it may be a good idea to extend the heapsnapshot format a little to support more such use cases (filed dart-lang/sdk#50546 for what came to my mind so far). Some things I had in mind were already done by @rmacnak-google - e.g. adding Smis in cl/265562

[mkustermann]

Cannot look at an object and follow successors, predecessors, dominator parent, dominator children, etc.

As a side note:

Personally I have found that dominator functionality of individual objects to be of limited use. If there's e.g. a string object that happens to be referred to by two objects, one may get a dominator that doesn't tell anything about how the string is referenced (dominator may be ObjectPool or something else very high up).
=> For individual objects I found shortest-retaining-path a much more useful functionality.

For aggregate views on memory the dominator-based graphexplorer functionality of boxes is more useful. Though it would be good to be able to make a heapsnapshot generation configurable to exclude VM-internal objects. That would prevent one to see ObjectPool or other such things dominating a lot of other objects (one of bullet points in dart-lang/sdk#50546 I filed)

[polina-c]

We can think of reusing/adopting an existing graph exploration language/tool.

For example:

• https://gephi.org/
• https://neo4j.com/developer/cypher/

[polina-c]

@bkonyi , can you itemize use cases and attach video demo on how observatory address them?

[polina-c]

Supported formats:
https://gephi.org/users/supported-graph-formats/