[SPARK-54840][SQL] OrcList Pre-allocation

[yaooqinn]

What changes were proposed in this pull request?

This PR optimizes ORC serialization performance by pre-allocating OrcList with the exact array size instead of relying on dynamic resizing.

Key changes:

• Pre-allocate OrcList with numElements from the input array
• Avoid multiple ArrayList resize operations and element copying during serialization
• Cache numElements value to avoid redundant calls in the loop condition

Why are the changes needed?

Problem:
When serializing arrays to ORC format, the current implementation creates an empty OrcList (which extends ArrayList) and grows it dynamically. For large arrays, this triggers multiple resize operations, each requiring:

1. Allocating a new larger backing array
2. Copying all existing elements to the new array
3. Discarding the old array

Performance Impact:
For an array with 65,536 elements, the default ArrayList growth pattern (1.5x capacity increase) causes ~16 resize operations, copying approximately 1 million elements in total.

Solution:
By pre-allocating the OrcList with the known size, we eliminate all resize operations and associated element copying, resulting in:

=== Resize Behavior Analysis: 1000000 elements ===
Target size: 1,000,000 elements
Total resizes: 29
Total elements copied: 2,430,972
Final capacity: 1,215,487

Resize sequence:
  1. Resize:     10 →     15 (copy     10 elements)
  2. Resize:     15 →     22 (copy     15 elements)
  3. Resize:     22 →     33 (copy     22 elements)
  4. Resize:     33 →     49 (copy     33 elements)
  5. Resize:     49 →     73 (copy     49 elements)
  6. Resize:     73 →    109 (copy     73 elements)
  7. Resize:    109 →    163 (copy    109 elements)
  8. Resize:    163 →    244 (copy    163 elements)
  9. Resize:    244 →    366 (copy    244 elements)
  10. Resize:    366 →    549 (copy    366 elements)
  11. Resize:    549 →    823 (copy    549 elements)
  12. Resize:    823 →  1,234 (copy    823 elements)
  13. Resize:  1,234 →  1,851 (copy  1,234 elements)
  14. Resize:  1,851 →  2,776 (copy  1,851 elements)
  15. Resize:  2,776 →  4,164 (copy  2,776 elements)
  16. Resize:  4,164 →  6,246 (copy  4,164 elements)
  17. Resize:  6,246 →  9,369 (copy  6,246 elements)
  18. Resize:  9,369 → 14,053 (copy  9,369 elements)
  19. Resize: 14,053 → 21,079 (copy 14,053 elements)
  20. Resize: 21,079 → 31,618 (copy 21,079 elements)
  21. Resize: 31,618 → 47,427 (copy 31,618 elements)
  22. Resize: 47,427 → 71,140 (copy 47,427 elements)
  23. Resize: 71,140 → 106,710 (copy 71,140 elements)
  24. Resize: 106,710 → 160,065 (copy 106,710 elements)
  25. Resize: 160,065 → 240,097 (copy 160,065 elements)
  26. Resize: 240,097 → 360,145 (copy 240,097 elements)
  27. Resize: 360,145 → 540,217 (copy 360,145 elements)
  28. Resize: 540,217 → 810,325 (copy 540,217 elements)
  29. Resize: 810,325 → 1,215,487 (copy 810,325 elements)

Overhead ratio: 2.43x
(For every element added, 2.43 elements are copied during resizes)

=== Testing Array Size: 1000000 ===
Array Size: 1,000,000 elements
Iterations: 50
Without pre-allocation: 1328.69 ms total (26.574 ms/iter)
With pre-allocation:    620.36 ms total (12.407 ms/iter)
Time saved:             708.33 ms (53.3% improvement)
Expected resize count:  29 times
Final capacity needed:  1215487

Does this PR introduce any user-facing change?

No. This is a performance optimization with no functional changes. The output remains identical.

How was this patch tested?

1. Existing Tests: All existing ORC-related tests pass, ensuring correctness is maintained
2. Performance Testing: see codeblock above

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Pull request overview

This PR optimizes ORC array serialization performance by pre-allocating OrcList with the exact array size instead of using dynamic resizing. The optimization eliminates multiple ArrayList resize operations and element copying, resulting in a ~53% performance improvement for large arrays (1M elements) based on the benchmark results in the PR description.

Key changes:

• Pre-allocate OrcList with known array size to avoid dynamic resizing
• Cache numElements() value to avoid redundant method calls in loop condition

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