GH-32381: [C++] Improve error handling for hash table merges

[kris-gaudel]

Rationale for this change

Fixes#32381

What changes are included in this PR?

Proper error handling in util/hashing.h and unit test for said error handling in util/hashing_test.cc

Are these changes tested?

Yes, via included unit test

Are there any user-facing changes?

Yes, error handling in hashing utilities

• GitHub Issue: [C++] Improve error handling for hash table merges #32381

[github-actions]

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[zanmato1984]

Thanks — the fix direction looks right to me overall, but I think there are two follow-ups worth addressing inline.

[kris-gaudel]

@zanmato1984 Anything else? I think I addressed everything

[zanmato1984]

General comment (helper refactor idea)

Nice work on propagating merge-time failures. One follow-up suggestion to make BinaryMemoTable::MergeTable a bit less awkward: since VisitValues(...) is void, the current implementation has to capture a Status and early-exit the visitor.

Consider adding a small helper that allows a fallible visitor, e.g.:

// Like VisitValues but allows the visitor to fail.// Visitor signature: Status(std::string_view).template <typename VisitFunc>
Status VisitValuesStatus(int32_t start, VisitFunc&& visit) const {
for (int32_t i = start; i < size(); ++i) {
RETURN_NOT_OK(visit(binary_builder_.GetView(i)));
}
returnStatus::OK();
}

and then implement merge as:

return other_table.VisitValuesStatus(0, [this](std::string_view v) {
int32_t unused;
returnthis->GetOrInsert(v, &unused);
});

(Your existing logic is totally fine; this is just a readability/style cleanup.)

[kris-gaudel]

@zanmato1984 thank you for the suggestions! Lmk what you think

[zanmato1984]

+1

Thanks for working on this!

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 3 benchmarking runs that have been run so far on merge-commit 70113a6.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 25 possible false positives for unstable benchmarks that are known to sometimes produce them.