1 | #pragma once |
2 | |
3 | #include <Columns/IColumn.h> |
4 | |
5 | |
6 | namespace DB |
7 | { |
8 | |
9 | /** Create a 'selector' to be used in IColumn::scatter method |
10 | * according to sharding scheme and values of column with sharding key. |
11 | * |
12 | * Each of num_shards has its weight. Weight must be small. |
13 | * 'slots' contains weight elements for each shard, in total - sum of all weight elements. |
14 | * |
15 | * Values of column get divided to sum_weight, and modulo of division |
16 | * will map to corresponding shard through 'slots' array. |
17 | * |
18 | * Column must have integer type. |
19 | * T is type of column elements. |
20 | */ |
21 | template <typename T> |
22 | IColumn::Selector createBlockSelector( |
23 | const IColumn & column, |
24 | const std::vector<UInt64> & slots); |
25 | |
26 | } |
27 | |