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…pl::Validate() `std::vector::reserve(delta_)` only guarantees `capacity() >= delta_`, not `capacity() == delta_`. When the standard library/allocator uses size-returning allocations (such as C++23 `allocate_at_least`), `reserve(delta_)` can immediately set `capacity() > delta_`, causing `TDigestImpl::Validate()` to fail with "oversized tdigest buffer" even when the number of centroids is at most `delta_`. Check `size() > delta_` instead of `capacity() > delta_` to verify that the tdigest buffer did not expand past `delta_` elements.
dmitry-chirkov-dremio
approved these changes
Oct 7, 2026
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Rationale for this change
std::vector::reserve(delta_)only guaranteescapacity() >= delta_, notcapacity() == delta_. When the C++ standard library and allocator use size-returning allocations (such as C++23allocate_at_least),reserve(delta_)can immediately setcapacity() > delta_, causingTDigestImpl::Validate()to fail with"oversized tdigest buffer"even when the number of centroids is at mostdelta_.What changes are included in this PR?
Check
tdigests_[0].size() > delta_ || tdigests_[1].size() > delta_instead ofcapacity() > delta_inTDigest::TDigestImpl::Validate().Are these changes tested?
Yes, covered by existing
TDigestTestunit tests incpp/src/arrow/util/tdigest_test.cc.Are there any user-facing changes?
No.
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