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#pragma once
#include <Columns/IColumn.h>
namespace DB
{
/** Create a 'selector' to be used in IColumn::scatter method
* according to sharding scheme and values of column with sharding key.
*
* Each of num_shards has its weight. Weight must be small.
* 'slots' contains weight elements for each shard, in total - sum of all weight elements.
*
* Values of column get divided to sum_weight, and modulo of division
* will map to corresponding shard through 'slots' array.
*
* Column must have integer type.
* T is type of column elements.
*/
template <typename T>
IColumn::Selector createBlockSelector(
const IColumn & column,
const std::vector<UInt64> & slots);
}
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