(arrow) branch main updated: [C++] Remove capacity() check in TDigest::TDigestImpl::Validate() (#52276)

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cyb70289 pushed a commit to branch main
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The following commit(s) were added to refs/heads/main by this push:
     new 740237e342c [C++] Remove capacity() check in 
TDigest::TDigestImpl::Validate() (#52276)
740237e342c is described below

commit 740237e342c647967279abf6b36f2e2fafe46181
Author: Evan Brown <e...@google.com>
AuthorDate: Thu Oct 15 23:05:56 2026 -0400

    [C++] Remove capacity() check in TDigest::TDigestImpl::Validate() (#52276)
    
    ### Rationale for this change
    
    `std::vector::reserve(delta_)` only guarantees `capacity() >= delta_`,
    not `capacity() == delta_`. When the C++ standard library and allocator
    use 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_`.
    
    Fixes issue #53777.
    
    ### What changes are included in this PR?
    
    Remove the check of `capacity() > delta_` in
    `TDigest::TDigestImpl::Validate()`.
    
    ### Are these changes tested?
    
    Yes, covered by existing `TDigestTest` unit tests in
    `cpp/src/arrow/util/tdigest_test.cc`.
    
    ### Are there any user-facing changes?
    
    No.
    
    ### Was AI used for this PR?
    
    **PR code and description written by:**
    
    - [x] Human
    - [x] AI
    
    **Reviewed before submission by:**
    
    - [x] Human
    - [ ] AI
    - [ ] Not reviewed
---
 cpp/src/arrow/util/tdigest.cc | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/cpp/src/arrow/util/tdigest.cc b/cpp/src/arrow/util/tdigest.cc
index 36a83fb336d..7d9e316cd30 100644
--- a/cpp/src/arrow/util/tdigest.cc
+++ b/cpp/src/arrow/util/tdigest.cc
@@ -168,10 +168,6 @@ class TDigest::TDigestImpl {
     if (total_weight != total_weight_) {
       return Status::Invalid("tdigest total weight mismatch");
     }
-    // check if buffer expanded
-    if (tdigests_[0].capacity() > delta_ || tdigests_[1].capacity() > delta_) {
-      return Status::Invalid("oversized tdigest buffer");
-    }
     // check k-size
     return merger_.Validate(tdigests_[current_], total_weight_);
   }