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new b818f93416 perf: Improve performance of `md5` (#19568)
b818f93416 is described below
commit b818f93416d18d06374a0707f5ef571f8a384070
Author: Andy Grove <[email protected]>
AuthorDate: Wed Dec 31 02:24:34 2025 -0700
perf: Improve performance of `md5` (#19568)
## Which issue does this PR close?
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enhancements and this helps us generate change logs for our releases.
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- Part of https://github.com/apache/datafusion/issues/19569
## Rationale for this change
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Why are you proposing this change? If this is already explained clearly
in the issue then this section is not needed.
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I ran microbenchmarks comparing DataFusion with DuckDB for string
functions (see https://github.com/apache/datafusion-benchmarks/pull/26)
and noticed that DF was very slow for `md5`.
This PR improves performance:
| Benchmark | Before | After | Speedup |
|----------------------------|--------|--------|-------------|
| md5_array (1024 strings) | 206 µs | 100 µs | 2.1x faster |
| md5_scalar (single string) | 337 ns | 221 ns | 1.5x faster |
## What changes are included in this PR?
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is sometimes worth providing a summary of the individual changes in this
PR.
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Avoid using `write!` with a format string and use a more efficient
approach
## Are these changes tested?
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## Are there any user-facing changes?
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---
datafusion/functions/src/crypto/basic.rs | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/datafusion/functions/src/crypto/basic.rs
b/datafusion/functions/src/crypto/basic.rs
index 5a7d891e0c..bda16684c8 100644
--- a/datafusion/functions/src/crypto/basic.rs
+++ b/datafusion/functions/src/crypto/basic.rs
@@ -33,7 +33,7 @@ use datafusion_common::{
use datafusion_expr::ColumnarValue;
use md5::Md5;
use sha2::{Sha224, Sha256, Sha384, Sha512};
-use std::fmt::{self, Write};
+use std::fmt;
use std::str::FromStr;
use std::sync::Arc;
@@ -157,14 +157,18 @@ pub fn md5(args: &[ColumnarValue]) ->
Result<ColumnarValue> {
})
}
-/// this function exists so that we do not need to pull in the crate hex. it
is only used by md5
-/// function below
+/// Hex encoding lookup table for fast byte-to-hex conversion
+const HEX_CHARS_LOWER: &[u8; 16] = b"0123456789abcdef";
+
+/// Fast hex encoding using a lookup table instead of format strings.
+/// This is significantly faster than using `write!("{:02x}")` for each byte.
#[inline]
fn hex_encode<T: AsRef<[u8]>>(data: T) -> String {
- let mut s = String::with_capacity(data.as_ref().len() * 2);
- for b in data.as_ref() {
- // Writing to a string never errors, so we can unwrap here.
- write!(&mut s, "{b:02x}").unwrap();
+ let bytes = data.as_ref();
+ let mut s = String::with_capacity(bytes.len() * 2);
+ for &b in bytes {
+ s.push(HEX_CHARS_LOWER[(b >> 4) as usize] as char);
+ s.push(HEX_CHARS_LOWER[(b & 0x0f) as usize] as char);
}
s
}
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