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perf: use 8KB buffer for local ObjectWriter #5907

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perf: use 8KB buffer for local ObjectWriter #5907

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24 changes: 21 additions & 3 deletions rust/lance-io/src/object_writer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,8 @@ pub struct ObjectWriter {
buffer: Vec<u8>,
// TODO: use constant size to support R2
use_constant_size_upload_parts: bool,
/// Local filesystem writes don't need 5MB multipart buffers.
is_local: bool,
}

#[derive(Debug, Clone, Default)]
Expand Down Expand Up @@ -157,20 +159,34 @@ impl UploadState {

impl ObjectWriter {
pub async fn new(object_store: &LanceObjectStore, path: &Path) -> Result<Self> {
let is_local = object_store.is_local();
let initial_capacity = if is_local {
8 * 1024 // 8 KB - no S3/GCS minimum part size for local filesystem
} else {
initial_upload_size() // 5 MB for cloud (S3/GCS minimum part size)
};
Ok(Self {
state: UploadState::Started(object_store.inner.clone()),
cursor: 0,
path: Arc::new(path.clone()),
connection_resets: 0,
buffer: Vec::with_capacity(initial_upload_size()),
buffer: Vec::with_capacity(initial_capacity),
use_constant_size_upload_parts: object_store.use_constant_size_upload_parts,
is_local,
})
}

/// Returns the contents of `buffer` as a `Bytes` object and resets `buffer`.
/// The new capacity of `buffer` is determined by the current part index.
fn next_part_buffer(buffer: &mut Vec<u8>, part_idx: u16, constant_upload_size: bool) -> Bytes {
let new_capacity = if constant_upload_size {
fn next_part_buffer(
buffer: &mut Vec<u8>,
part_idx: u16,
constant_upload_size: bool,
is_local: bool,
) -> Bytes {
let new_capacity = if is_local {
8 * 1024 // 8 KB for local filesystem
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@westonpace westonpace Feb 9, 2026

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Is this going to chop up large writes into tiny 8KiB writes? From a syscall perspective that maybe isn't the best approach. We should probably just send the entire buffer to the OS?

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@wkalt wkalt Feb 10, 2026

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hmm, actually this is way worse than I thought. It is going to do a simulated multipart write on the local FS.

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@wjones127 wjones127 Feb 10, 2026

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I prototyped a specialized local writer here that doesn't do the multipart simulation. I didn't see an improvement in write throughput, so left it aside, but feel free to play around with it. wjones127@7d7e30a

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@wkalt wkalt Feb 11, 2026

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this works perfectly 👍

} else if constant_upload_size {
// The store does not support variable part sizes, so use the initial size.
initial_upload_size()
} else {
Expand Down Expand Up @@ -222,6 +238,7 @@ impl ObjectWriter {
&mut mut_self.buffer,
0,
mut_self.use_constant_size_upload_parts,
mut_self.is_local,
);
futures.spawn(Self::put_part(upload.as_mut(), data, 0, None));

Expand Down Expand Up @@ -401,6 +418,7 @@ impl AsyncWrite for ObjectWriter {
&mut mut_self.buffer,
*part_idx,
mut_self.use_constant_size_upload_parts,
mut_self.is_local,
);
futures.spawn(
Self::put_part(upload.as_mut(), data, *part_idx, None)
Expand Down
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