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75 lines
3.2 KiB
Markdown
75 lines
3.2 KiB
Markdown
# Semantic Diff Problems (Mini-Summit)
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### Performance (most significant problem)
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- SES / Alignment are biggest time / space consumers.
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- Profiling small subsets of code paths rather than the full context.
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- Adding more criterion benchmarks for code paths not currently profiled (like Diff Summaries).
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##### Alignment performance
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- Has to visit each child of each remaining line.
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##### [SES](https://github.com/github/semantic-diff/files/22485/An.O.ND.Difference.Algorithm.and.its.Variations.pdf) Performance
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- n^3 the size of the tree.
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- Can try bounded SES (looks ahead by a fixed size of nodes).
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- Identify more comparisons we can skip (i.e. don't compare functions with array literals).
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- Does not look like there are more easy wins here (algorithm is already implemented to prevent unnecessary comparisions).
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- In some cases, the diffing is expensive because we don't have more fine-grain identifiers for certain diffs. (e.g. a test file with 100 statement expressions).
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- Diffing against identifiers (use the edit distance to determine whether to compare terms with SES or not).
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- This could result in us missing a function rename though.
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- Not a catchall, but it can help increase performance in a larger number of cases.
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##### [RWS](https://github.com/github/semantic-diff/files/325837/RWS-Diff.Flexible.and.Efficient.Change.Detection.in.Hierarchical.Data.pdf) Performance
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- Random Walk Similarity.
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- computes approximation to the minimal edit script.
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- O(log N) rather than O(n^3).
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- RWS does not rely on identifiers.
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- RWS solves our performance problem in the general form.
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- Can allow us to diff patches of patches (something we cannot do currently with our implementation of SES).
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##### Diff summaries performance
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- Performance of DS is dependent on diffing (Diff Terms, Interpreter, cost functions)
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### Failing too hard
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- Request is not completing if Semantic Diff fails.
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- How can we fail better on dotcom?
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- How can we fail better when parsing? (both in Semantic Diff and dotcom)
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### Responsiveness
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- Async fetch diff summaries / diffs / progressive diffs or diff summaries
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### Improving grammars
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- Fix Ruby parser.
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- Testing and verifying other grammars.
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### Measure effectiveness of grammars
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### Tooling
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- Why isn't parallelization of SES having the expected effect?
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- Should focus on low hanging fruit but we're not going to write a debugger.
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### Time limitations with respect to solutions and team
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### Ramp up time is extremely variable.
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### Onboarding
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- Pairing has been fantastic.
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- SES algorithm requires some context and background to understand the code at the general / macro level.
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- Plan a bit before pairing to gain context.
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### Pre-launch Ideas
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- Test on a couple file server nodes and run semantic diff on javascript repos.
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- Collect repos, files, shas that contain error nodes to gain a % of error rates and expose errors in tree sitter grammars.
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- If sources have errors, can we use a parser that validates the source is correct?
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- Configure a script that is as language independent as possible that can automate the error collection process but allows us to specify an independent validating parser for each language.
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