arrow

ARROW-8516: [Rust] Improve PrimitiveBuilder::append_slice performance

BufferBuilder<BooleanType>::append_slice is called by PrimitiveBuilder::append_slice with a constructed vector of true values.

Even in release builds the associated allocations and iterations are not optimised out, resulting in a third of the time to parse a parquet file containing single integers being spent in PrimitiveBuilder::append_slice.

This PR adds an append_n method to the BufferBuilderTrait that allows this to be handled more efficiently. My rather unscientific testing shows it to halve the amount of time spent in this method yielding an ~20% speedup for my particular workload.

Closes #6980 from tustvold/master

Authored-by: Raphael Taylor-Davies <r.taylordavies@googlemail.com>
Signed-off-by: Paddy Horan <paddyhoran@hotmail.com>