GH-26648: [C++] Optimize union equality comparison #26648

[mcshawn10]

Rationale for this change

#26648 proposes an optimization in checking sparse array equality by detecting contiguous runs, this PR implements that change

What changes are included in this PR?

previously, sparse array comparison was checked one by one, in this change, contiguous runs are detected and compared by checking equality of current and previous child_ids

Are these changes tested?

already covered by existing unit tests

Are there any user-facing changes?

no

• GitHub Issue: [C++] Optimize union equality comparison #26648

[github-actions]

⚠️ GitHub issue #26648 has been automatically assigned in GitHub to PR creator.

[mapleFU]

Thanks! By the way is there any benchmark result for this pr?

[mcshawn10]

Thanks! By the way is there any benchmark result for this pr?

still figuring that part out! 😅

[mcshawn10]

overall.json

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Non-regressions: (6)
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                              benchmark          baseline          contender  change %                                                                                                                                                                                                   counters
    ArrayRangeEqualsSparseUnion/65536/0 47.119M items/sec 105.533M items/sec   123.973      {'family_index': 0, 'per_family_instance_index': 5, 'run_name': 'ArrayRangeEqualsSparseUnion/65536/0', 'repetitions': 1, 'repetition_index': 0, 'threads': 1, 'iterations': 506, 'null_percent': 0.0}
  ArrayRangeEqualsSparseUnion/65536/100 29.924M items/sec  57.186M items/sec    91.101    {'family_index': 0, 'per_family_instance_index': 1, 'run_name': 'ArrayRangeEqualsSparseUnion/65536/100', 'repetitions': 1, 'repetition_index': 0, 'threads': 1, 'iterations': 326, 'null_percent': 1.0}
ArrayRangeEqualsSparseUnion/65536/10000 30.820M items/sec  57.887M items/sec    87.826 {'family_index': 0, 'per_family_instance_index': 0, 'run_name': 'ArrayRangeEqualsSparseUnion/65536/10000', 'repetitions': 1, 'repetition_index': 0, 'threads': 1, 'iterations': 325, 'null_percent': 0.01}
   ArrayRangeEqualsSparseUnion/65536/10 30.616M items/sec  56.025M items/sec    82.990    {'family_index': 0, 'per_family_instance_index': 2, 'run_name': 'ArrayRangeEqualsSparseUnion/65536/10', 'repetitions': 1, 'repetition_index': 0, 'threads': 1, 'iterations': 331, 'null_percent': 10.0}
    ArrayRangeEqualsSparseUnion/65536/1 46.987M items/sec  82.663M items/sec    75.926    {'family_index': 0, 'per_family_instance_index': 4, 'run_name': 'ArrayRangeEqualsSparseUnion/65536/1', 'repetitions': 1, 'repetition_index': 0, 'threads': 1, 'iterations': 488, 'null_percent': 100.0}
    ArrayRangeEqualsSparseUnion/65536/2 31.326M items/sec  54.119M items/sec    72.760     {'family_index': 0, 'per_family_instance_index': 3, 'run_name': 'ArrayRangeEqualsSparseUnion/65536/2', 'repetitions': 1, 'repetition_index': 0, 'threads': 1, 'iterations': 340, 'null_percent': 50.0}