feat(tracing): Add read flow traces

[thrivikram-karur-g]

Description

Adding read flow traces for flows like file cache read, file cache write, file cache with parallel downloads,

Link to the issue in case of a bug fix.

b/454481823

Testing details

1. Manual - NA
2. Unit tests - NA
3. Integration tests - NA

Any backward incompatible change? If so, please explain.

NA

[gemini-code-assist]

Summary of Changes

Hello @thrivikram-karur-g, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the observability of read operations by introducing a new tracing framework based on OpenTelemetry. It integrates tracing into critical read paths, including file caching and direct GCS reads, to provide detailed insights into performance and potential bottlenecks. The changes allow for better understanding and debugging of how data is accessed and processed within the system.

Highlights

• New Tracing Package: A new tracing package has been introduced, providing an abstraction layer for distributed tracing. It includes a TraceHandle interface with noopTracer and otelTracer implementations, allowing for flexible integration with OpenTelemetry.
• Read Flow Tracing Integration: Comprehensive tracing has been integrated into various read-related components, including buffered reads, file cache operations (read, write, and parallel downloads), and direct GCS reader paths. This enables detailed visibility into the performance of read operations.
• Context Propagation and Error Recording: Tracing contexts are now properly propagated across function calls, ensuring that spans are correctly linked in distributed traces. Errors encountered during read operations are also recorded within their respective spans for easier debugging.
• Detailed Span Attributes: Specific attributes, such as gcsfuse.is_cache_hit and gcsfuse.bytes_read, are added to read-related spans. These attributes provide granular details about cache performance and data transfer, enhancing observability.

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[gemini-code-assist]

Code Review

This pull request introduces distributed tracing for read flows by adding a new tracing package and integrating it throughout the read path. The changes are well-structured, introducing a TraceHandle interface with noop and otel implementations, and using it to trace operations like file cache reads and downloads.

I have a few suggestions to improve the trace context propagation and the consistency of span naming. Overall, this is a great addition for observability.

[gemini-code-assist]

Using context.Background() here starts a new trace, which will not be a child of the parent operation's trace (e.g., ReadFile). This breaks the trace context propagation.

To fix this, the context.Context from the ReadWithReadManager call in internal/fs/handle/file.go should be propagated down to NewBufferedReader. This can be done by:

1. Adding a Ctx context.Context field to read_manager.ReadManagerConfig and bufferedread.BufferedReaderOptions.
2. Updating read_manager.NewReadManager to accept a context and pass it through the options.
3. Using the propagated context here instead of context.Background().

This will ensure that the ReadPrefetchBlockPoolGen span is correctly parented under the ongoing operation's span.

[gemini-code-assist]

Using reflect.TypeOf(r).String() for span names makes the tracing dependent on the internal type names, which can be brittle. For example, if a type is renamed or moved, the span name will change unexpectedly. A more robust approach would be to use string constants for span names for each reader type.