feat: add size to object store tracing

[wjones127]

• Adds size field to object store traces
• Formats paths with .as_ref(), so they aren't wrapped in debug representation of Path.

[github-actions]

PR Review: feat: add size to object store tracing

Overall this is a useful enhancement for observability. A few items to consider:

P1: Potential issue with get size reporting

In get(), the code records res.meta.size as the size field:

span.record("size", res.meta.size);

However, get() returns the entire object, but in get_opts() you record res.range.end - res.range.start:

span.record("size", res.range.end - res.range.start);

For get() without options, res.meta.size is the correct choice. But there's a subtle inconsistency: get_opts() uses the range size (bytes actually read), while get() uses metadata size. This is actually correct behavior since get() fetches the whole object, but it might be clearer to document this distinction or use res.range consistently for both.

P1: Multipart size recorded after completion only

The multipart upload size is recorded only in complete():

async fn complete(&mut self) -> OSResult<PutResult> {
    let res = self.target.complete().await?;
    self.write_span.record("size", self.write_size);
    Ok(res)
}

If abort() is called instead of complete(), the size won't be recorded. This may be intentional (aborted uploads aren't meaningful), but worth confirming.

P0: Missing debug_span import removal

The diff shows debug_span is removed from the import statement in favor of using tracing::Span::current(), but looking at the current file (line 18), the import still includes debug_span:

use tracing::{debug_span, instrument, Instrument, Span};

If this is no longer used, the unused import will likely cause a compiler warning. Please verify this was addressed.

[codecov]

Codecov Report

❌ Patch coverage is 99.46237% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
rust/lance-io/src/object_store/tracing.rs	99.46%	1 Missing ⚠️

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