Skip zero-init of output buffer#7996
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`BufferMut::with_capacity(total_len).push_n(0u8, total_len)` issues a
memset of the entire output range, only to have every byte overwritten
by the encoders. The encoders cover every byte by construction:
- Fixed-width non-null slots: sentinel + value bytes.
- Fixed-width null slots: sentinel + explicit per-byte zero-fill loop.
- Varlen blocks: full blocks are written by `encode_varlen_value`; the
partial-block tail is zero-padded by that same function.
- Struct/FSL null bodies: zero-filled after the child encoders run.
Switch to `unsafe { out_buf.set_len(total_len) }` with a SAFETY comment
recording the invariant. Reclaims a `total_len`-byte memset per call;
for varlen-heavy inputs (multiple MB of output) this saves real time.
dict_utf8 (varlen heavy) throughput: ~3.74 GB/s → ~4.55 GB/s.
Signed-off-by: Claude <noreply@anthropic.com>
This was referenced May 18, 2026
This was referenced May 18, 2026
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Merging this PR will not alter performance
|
| Mode | Benchmark | BASE |
HEAD |
Efficiency | |
|---|---|---|---|---|---|
| ⚡ | Simulation | chunked_varbinview_into_canonical[(100, 100)] |
358.4 µs | 325 µs | +10.26% |
| ⚡ | Simulation | chunked_varbinview_canonical_into[(1000, 10)] |
197.9 µs | 161.9 µs | +22.25% |
| ❌ | Simulation | chunked_varbinview_canonical_into[(100, 100)] |
273.3 µs | 309 µs | -11.56% |
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Comparing claude/row-c11-skip-zero-init (a358479) with develop (faf7e42)1
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Part 11 of 25 in the stacked PR series adding
vortex-row.This PR contains exactly one commit; review just that diff in isolation.
What this commit does
BufferMut::with_capacity(total_len).push_n(0u8, total_len)issues a memset of the entire output range, only to have every byte overwritten by the encoders. The encoders cover every byte by construction:encode_varlen_value; the partial-block tail is zero-padded by that same function.Switches to
unsafe { out_buf.set_len(total_len) }with a SAFETY comment recording the invariant. Reclaims atotal_len-byte memset per call; for varlen-heavy inputs (multiple MB of output) this saves real time. dict_utf8 (varlen heavy) throughput: ~3.74 GB/s → ~4.55 GB/s.Stack
claude/row-c01-crate-scaffoldingclaude/row-c02-sortfield-optionsclaude/row-c03-codec-fixed-widthclaude/row-c04-codec-varlenclaude/row-c05-codec-nestedclaude/row-c06-rowsize-scalarfnclaude/row-c07-rowencode-scalarfnclaude/row-c08-convert-columns-tests-benchclaude/row-c09-skip-listview-validationclaude/row-c10-validity-fast-pathclaude/row-c11-skip-zero-initclaude/row-c12-vectorize-pure-fixed-offsetsclaude/row-c13-vectorize-mixed-offsetsclaude/row-c14-varlen-block-copy-nonoverlappingclaude/row-c15-walk-varbinview-directlyclaude/row-c16-arith-write-fast-pathclaude/row-c17-specialize-constant-arithclaude/row-c18-kernel-dispatch-helpersclaude/row-c19-inventory-registryclaude/row-c20-constant-kernelclaude/row-c21-dict-kernelclaude/row-c22-patched-kernelclaude/row-c23-runend-kernelclaude/row-c24-bitpacked-kernelclaude/row-pr3-kernelsBase of this PR: #7995 (
claude/row-c10-validity-fast-path)Next in stack: #7997 (
claude/row-c12-vectorize-pure-fixed-offsets)Combined context
For the full design + rationale, see PR #7985 (top of stack).