yaommen a0a2942ad5 fix: respect max_batch_length for Rust vector and hybrid queries (#3172)
Fixes #1540

I could not reproduce this on current `main` from Python, but I could
still reproduce it from the Rust SDK.

Python no longer reproduces because the current Python vector/hybrid
query paths re-chunk results into a `pyarrow.Table` before returning
batches. Rust still reproduced because `max_batch_length` was passed
into planning/scanning, but vector search could still emit larger
`RecordBatch`es later in execution (for example after KNN / TopK), so it
was not enforced on the final Rust output stream.

This PR enforces `max_batch_length` on the final Rust query output
stream and adds Rust regression coverage.

Before the fix, the Rust repro produced:
`num_batches=2, max_batch=8192, min_batch=1808, all_le_100=false`

After the fix, the same repro produces batches `<= 100`.

## Runnable Rust repro

Before this fix, current `main` could still return batches like `[8192,
1808]` here even with `max_batch_length = 100`:

```rust
use std::sync::Arc;

use arrow_array::{
    types::Float32Type, FixedSizeListArray, RecordBatch, RecordBatchReader, StringArray,
};
use arrow_schema::{DataType, Field, Schema};
use futures::TryStreamExt;
use lancedb::query::{ExecutableQuery, QueryBase, QueryExecutionOptions};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let tmp = tempfile::tempdir()?;
    let uri = tmp.path().to_str().unwrap();

    let rows = 10_000;
    let schema = Arc::new(Schema::new(vec![
        Field::new("id", DataType::Utf8, false),
        Field::new(
            "vector",
            DataType::FixedSizeList(Arc::new(Field::new("item", DataType::Float32, true)), 4),
            false,
        ),
    ]));

    let ids = StringArray::from_iter_values((0..rows).map(|i| format!("row-{i}")));
    let vectors = FixedSizeListArray::from_iter_primitive::<Float32Type, _, _>(
        (0..rows).map(|i| Some(vec![Some(i as f32), Some(1.0), Some(2.0), Some(3.0)])),
        4,
    );
    let batch = RecordBatch::try_new(schema.clone(), vec![Arc::new(ids), Arc::new(vectors)])?;
    let reader: Box<dyn RecordBatchReader + Send> = Box::new(
        arrow_array::RecordBatchIterator::new(vec![Ok(batch)].into_iter(), schema),
    );

    let db = lancedb::connect(uri).execute().await?;
    let table = db.create_table("test", reader).execute().await?;

    let mut opts = QueryExecutionOptions::default();
    opts.max_batch_length = 100;

    let mut stream = table
        .query()
        .nearest_to(vec![0.0, 1.0, 2.0, 3.0])?
        .limit(rows)
        .execute_with_options(opts)
        .await?;

    let mut sizes = Vec::new();
    while let Some(batch) = stream.try_next().await? {
        sizes.push(batch.num_rows());
    }

    println!("{sizes:?}");
    Ok(())
}
```

Signed-off-by: yaommen <myanstu@163.com>
2026-03-30 15:43:58 -07:00
2023-03-17 18:15:19 -07:00
2025-03-10 09:01:23 -07:00

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