feat(iceberg): log warning when available_parallelism falls back to default#2520
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blackmwk merged 1 commit intoMay 28, 2026
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…efault When `std::thread::available_parallelism()` fails, `available_parallelism()` silently falls back to `DEFAULT_PARALLELISM` (= 1). Both call sites (`TableScanBuilder::new`, `ArrowReaderBuilder::new`) use this value to size their internal concurrency, so a silent fallback turns parallel execution into serial with no signal to the operator. Emit a `tracing::warn!` carrying the underlying error so the degraded state is observable. Resolves the existing `TODO` in `util::available_parallelism`. The `iceberg` crate gains a direct `tracing` dependency; `tracing` is already declared at the workspace level and is the agreed logging facade (see apache#482).
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Thanks @huan233usc for this pr!
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Which issue does this PR close?
Resolves the in-code
TODOatcrates/iceberg/src/util/mod.rs:40(no tracking issue).What changes are included in this PR?
When
std::thread::available_parallelism()fails,available_parallelism()falls back toDEFAULT_PARALLELISM(= 1). Both call sites —TableScanBuilder::newandArrowReaderBuilder::new— use this value to size their internal concurrency, so a silent fallback turns parallel execution into serial with no signal to the operator.This PR emits a
tracing::warn!carrying the underlying error so the degraded state is observable, e.g.:The
icebergcrate gains a directtracingdependency.tracingis already declared at the workspace level and is the agreed logging facade (per the conclusion of #482).Are these changes tested?
No new unit test.
std::thread::available_parallelism()succeeds on every standard CI environment and cannot be forced to fail without mocking the standard library, so a fallback-path test would require either:cfg(test)indirection layer to inject a mockavailable_parallelism(), orBoth seemed disproportionate for a one-line observability change. Existing callers (
TableScanBuilder,ArrowReaderBuilder) continue to receive a validNonZeroUsizeon success, exercised by the existing test suite. Happy to add either approach if reviewers prefer.Verified locally:
cargo check -p icebergcargo test -p iceberg --lib util::cargo clippy -p iceberg --all-targets -- -D warningscargo fmt -p iceberg --check