timsaucer opened a new pull request, #7437:
URL: https://github.com/apache/arrow-rs/pull/7437
# Which issue does this PR close?
None, but I can open one if necessary.
# Rationale for this change
The ordering of metadata is not consistent since it uses a HashMap. It can
be useful in unit tests to verify an output from a known hash of it's
serialized values. With metadata this is not consistent.
# What changes are included in this PR?
Adds ordering to the hashmap keys when encoding.
# Are there any user-facing changes?
No.
# Example
If you run this example multiple times, you will see the encoding changes
from run to run based on the non-deterministic ordering of the hashmap iterator.
```rust
use std::{hash::Hasher, sync::Arc};
use arrow::{array::RecordBatch, datatypes::Schema};
fn main() {
let schema = Arc::new(
Schema::empty().with_metadata(
[
("a".to_owned(), "1".to_owned()), //
("b".to_owned(), "2".to_owned()), //
("c".to_owned(), "3".to_owned()), //
("d".to_owned(), "4".to_owned()), //
("e".to_owned(), "5".to_owned()), //
]
.into_iter()
.collect(),
),
);
let batch = RecordBatch::new_empty(schema.clone());
dbg!(&batch.schema().metadata().keys());
let mut bytes = Vec::new();
let mut w = arrow::ipc::writer::StreamWriter::try_new(&mut bytes,
&schema).unwrap();
w.write(&batch).unwrap();
w.finish().unwrap();
let mut h = std::hash::DefaultHasher::new();
h.write(&bytes);
let h = h.finish();
eprintln!("{} bytes -- h = {h:x}", bytes.len());
}
```
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