[release/9.0] Mitigate JsonObject performance regression. #108014
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Backport of #107944 to release/9.0
/cc @eiriktsarpalis
Customer Impact
In .NET 9 the
JsonObjectimplementation was retargeted to the newly publishedSystem.Collections.Generic.OrderedDictionarycollection, replacing a bespoke collection implementation. The change left a suboptimal implementation in its indexer, resulting in a ~70% performance regression when constructing new objects.Regression
Regressed by #103645.
Testing
Added relevant benchmarks to dotnet/performance.
Risk
Medium. The fix involves using different APIs on the brand new
OrderedDictionarytype so there is risk that this might surface other undiscovered bugs.