split: stream data using copy to not overwhelm memory with large files

[ChrisDryden]

This should solve the issue: #10250 where for large files split can run out of memory. I was able to use the built in integration test support to limit the resources that the test has to mock a scenario where the file is larger than the available memory to trigger the conditions for the bug.

[codspeed-hq]

Merging this PR will improve performance by ×4.6

⚡ 4 improved benchmarks
✅ 278 untouched benchmarks
⏩ 38 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Memory	split_number_chunks	1,148.1 KB	249.9 KB	×4.6
⚡	Memory	sort_numeric[500000]	48.7 MB	47.3 MB	+3.07%
⚡	Memory	sort_key_field[500000]	32.8 MB	31.4 MB	+4.65%
⚡	Simulation	split_number_chunks	290.2 µs	258 µs	+12.47%

---

_{Comparing ChrisDryden:fix-split-number-memory-issue (694c8a2) with main (8a7c3fb)}

Footnotes

1. 38 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[sylvestre]

@ChrisDryden what is your take on the perf regression ?

[ChrisDryden]

I don't think the perf regression is acceptable, right now io::copy uses a 8kb buffer which is causing the regression. I see head uses a 64kb buffer instead, I'll try seeing if the increased buffer size will mitigate the perf regression

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)

[ChrisDryden]

Much better now, solved the original issue and there's huge memory and performance improvements. The original fix had a 8kb default buffer and testing locally I found it hit diminishing returns at 128kb.