perf: improve performance of spark hex function
#19738
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Jefffrey
reviewed
Jan 11, 2026
| let hex_string = hex_encode(bytes, lowercase); | ||
| Ok(hex_string) | ||
| /// Generic hex encoding for int64 type | ||
| fn hex_encode_int64<I>(iter: I, len: usize) -> Result<ColumnarValue, DataFusionError> |
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nit: this doesnt need to be generic since its only used for int64 arrays
| for v in iter { | ||
| if let Some(num) = v { | ||
| buffer.clear(); | ||
| hex_int64(num, &mut buffer); |
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I find it a little interesting how we have this buffer across iterations here, but then inside hex_int64 we have another buffer, which is used to copy into this outer buffer. Can we unify them somehow?
| buffer.clear(); | ||
| hex_int64(num, &mut buffer); | ||
| unsafe { | ||
| builder.append_value(from_utf8_unchecked(&buffer)); |
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nit: would be good to add a safety comment, even if its just something like
SAFETY: all chars are from
HEX_CHARS_UPPERwhich are valid ascii
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| while n != 0 { | ||
| i -= 1; | ||
| let digest = (n & 0xF) as u8; | ||
| temp[i] = HEX_CHARS_UPPER[digest as usize]; | ||
| n >>= 4; | ||
| } |
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Would it make a performance difference if we unroll this loop manually, given we know the upper limit of iterations needed?
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Which issue does this PR close?
Rationale for this change
The current
hexfunction implementation usesformat!macro andStringArray::fromiterator pattern, which causes:Stringviaformat!What changes are included in this PR?
This PR optimizes the
hexencoding by:format!("{num:X}")with a fast lookup table approachStringBuilderBenchmark Results
Are these changes tested?
Yes. Existing units and sqllogictest tests pass. New benchmarks added.
Are there any user-facing changes?
No.