ClickHouse/dbms/src/DataStreams/narrowBlockInputStreams.cpp

#include <DB/DataStreams/ConcatBlockInputStream.h>


namespace DB
{

BlockInputStreams narrowBlockInputStreams(BlockInputStreams & inputs, size_t width)
{
	size_t size = inputs.size();
	if (size <= width)
		return inputs;

	std::vector<BlockInputStreams> partitions(width);

	typedef std::vector<size_t> Distribution;
	Distribution distribution(size);

	for (size_t i = 0; i < size; ++i)
		distribution[i] = i % width;

	std::random_shuffle(distribution.begin(), distribution.end());

	for (size_t i = 0; i < size; ++i)
		partitions[distribution[i]].push_back(inputs[i]);

	BlockInputStreams res(width);
	for (size_t i = 0; i < width; ++i)
		res[i] = new ConcatBlockInputStream(partitions[i]);

	return res;
}

}