[ARROW-11647] [C++][Compute] CastFromNull does not use preallocated buffers

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: C++
• External issue URL: https://github.com/apache/arrow/issues/27510
• Assignee: Unassigned
• Reporter: Ben Kietzman
• Created: 16/Feb/21 18:38
• Updated: 11/Jan/23 08:21

Description

When casting from null, currently new buffers are allocated for every batch of the computation. This is wasteful as for simple types data buffers are preallocated and the null bitmap is handled separately; CastFromNull need do no work at all (unless we decide to explicitly zero the data buffer). For varlength out types the offsets buffer is preallocated and should be zeroed, for struct types preallocation is not implemented (but should be as simple as preallocating each child array).

Issue Links

• is related to: ARROW-13121 [C++][Compute] Extract preallocation logic from KernelExecutor