feat(profiling): add ProfilesDictionary #1349
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BenchmarksComparisonBenchmark execution time: 2025-11-19 22:08:07 Comparing candidate commit 89b7a8e in PR branch Found 0 performance improvements and 1 performance regressions! Performance is the same for 54 metrics, 2 unstable metrics. scenario:benching deserializing traces from msgpack to their internal representation
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BaselineOmitted due to size. |
Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## main #1349 +/- ##
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- Coverage 71.19% 71.15% -0.04%
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Files 392 396 +4
Lines 62677 62798 +121
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+ Hits 44622 44685 +63
- Misses 18055 18113 +58
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Artifact Size Benchmark Reportaarch64-alpine-linux-musl
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KowalskiThomas
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KowalskiThomas
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What I see makes sense to me but I'll let someone better versed in Rust make review!
danielsn
reviewed
Nov 18, 2025
| /// Pprof representations. Omits the start line to save space because Datadog | ||
| /// doesn't use this in any way. | ||
| #[derive(Copy, Clone, Debug, Default, Eq, PartialEq, Hash)] | ||
| #[repr(C)] |
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Is there a reason for this to be repr[c]?
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Yes, although I haven't looked to see if this messes up cbindgen. Sometimes a repr(C) will cause it to pick up this definition instead of some other definition, since it doesn't understand modules and namespaces.
The reason is that it makes Function and Function2 layout-compatible, aside from the case of a null StringId2. Converting from Function to Function2 is free, and the reverse is just the code required to coerce nulls into empty strings.
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Just checked and no differences in API (yet):
cargo clean
git switch levi/profiles_dictionary
cargo run --bin release --features profiling --release -- --out $PWD/release2
cargo clean
git switch main
cargo run --bin release --features profiling --release -- --out $PWD/release1
diff release{1,2}/include/datadog/profiling.h
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Do we have an assertion or test that would fail if the two are not compatible?
| } | ||
| } | ||
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| impl From<Function2> for Function { |
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Not for this PR, but it feels like someone OUGHT to have a crate to do this
| /// `FunctionId2` converts to a `None`. | ||
| /// | ||
| /// # Safety | ||
| /// The pointer object must still be alive. In general this means the |
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I don't think so. If the profiles dictionary is alive, this should be safe.
danielsn
reviewed
Nov 21, 2025
| /// Pprof representations. Omits the start line to save space because Datadog | ||
| /// doesn't use this in any way. | ||
| #[derive(Copy, Clone, Debug, Default, Eq, PartialEq, Hash)] | ||
| #[repr(C)] |
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Do we have an assertion or test that would fail if the two are not compatible?
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| /// performed on; it is not generally guaranteed that ids from one dictionary | ||
| /// can be used in another dictionary, even if it happens to work by | ||
| /// implementation detail. |
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Is there any way to detect this error?
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What does this PR do?
This adds the ProfilesDictionary data structure, which holds deduplicated functions, mappings, and strings and gives back IDs to the inserted elements.
Motivation
This is another stepping stone for my new profiling API with long-lived functions, mappings, and strings.
Additional Notes
This is stacked on top of PR #1347.
How to test the change?
Regular testing applies, just additions here (that are currently unused).