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Posted to github@datafusion.apache.org by "andygrove (via GitHub)" <gi...@apache.org> on 2025/12/30 20:26:54 UTC
[PR] perf: Improve performance of `md5` [datafusion]
andygrove opened a new pull request, #19568:
URL: https://github.com/apache/datafusion/pull/19568
## Which issue does this PR close?
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- Closes #.
## Rationale for this change
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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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There is no need to duplicate the description in the issue here but it 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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Re: [PR] perf: Improve performance of `md5` [datafusion]
Posted by "viirya (via GitHub)" <gi...@apache.org>.
viirya commented on code in PR #19568:
URL: https://github.com/apache/datafusion/pull/19568#discussion_r2654161351
##########
datafusion/functions/src/crypto/basic.rs:
##########
@@ -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.
Review Comment:
It's a bit weird to put the comment here. Maybe put on top of `HEX_CHARS_LOWER` lookup code.
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Re: [PR] perf: Improve performance of `md5` [datafusion]
Posted by "andygrove (via GitHub)" <gi...@apache.org>.
andygrove commented on code in PR #19568:
URL: https://github.com/apache/datafusion/pull/19568#discussion_r2653924382
##########
datafusion/functions/src/crypto/basic.rs:
##########
@@ -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 {
Review Comment:
I tried this, but the difference is tiny, so it may not be worth it.
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Re: [PR] perf: Improve performance of `md5` [datafusion]
Posted by "comphead (via GitHub)" <gi...@apache.org>.
comphead commented on code in PR #19568:
URL: https://github.com/apache/datafusion/pull/19568#discussion_r2653906392
##########
datafusion/functions/src/crypto/basic.rs:
##########
@@ -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 {
Review Comment:
great, curious if that would be more performance if create a string directly from bytes without utf checks(which is redundant ) and extract casts?
```
let bytes = data.as_ref();
let mut out = Vec::with_capacity(bytes.len() * 2);
for &b in bytes {
out.push(HEX_CHARS_LOWER[(b >> 4) as usize]);
out.push(HEX_CHARS_LOWER[(b & 0x0f) as usize]);
}
unsafe { String::from_utf8_unchecked(out) }
```
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Re: [PR] perf: Improve performance of `md5` [datafusion]
Posted by "Dandandan (via GitHub)" <gi...@apache.org>.
Dandandan merged PR #19568:
URL: https://github.com/apache/datafusion/pull/19568
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