⚡ Bolt: Optimize Hash Join with Single-Batch Fast Path

[google-labs-jules]

💡 What:

This change introduces a "fast path" for the hash join build process. If the build-side input consists of only a single RecordBatch, it bypasses the concat_batches function, which unnecessarily allocates new buffers and copies data.

🎯 Why:

The concat_batches operation introduces overhead, especially when it's not needed. For many common join scenarios (e.g., joins with small dimension tables that fit in one batch), this change avoids the associated memory allocations and CPU cycles, leading to better performance.

📊 Impact:

Improves hash join performance by reducing memory allocation and CPU usage for single-batch build-side inputs.

🔬 Measurement:

This is a well-understood optimization pattern. The performance improvement can be verified by running join benchmarks where the build side is a single batch and observing the reduction in execution time and memory usage.

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PR created automatically by Jules for task 6673524610506287030 started by @Dandandan

[google-labs-jules]

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