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4593d363d1
* Fix poor scalability of INSERT into Distributed table [#CLICKHOUSE-2791]. * Fix poor scalability of INSERT into Distributed table (continued) [#CLICKHOUSE-2791]. * Misc [#CLICKHOUSE-2791]. * Fixed error [#CLICKHOUSE-2791].
28 lines
716 B
C++
28 lines
716 B
C++
#pragma once
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#include <DB/Columns/IColumn.h>
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namespace DB
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{
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/** Create a 'selector' to be used in IColumn::scatter method
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* according to sharding scheme and values of column with sharding key.
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*
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* Each of num_shards has its weight. Weight must be small.
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* 'slots' contains weight elements for each shard, in total - sum of all weight elements.
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*
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* Values of column get divided to sum_weight, and modulo of division
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* will map to corresponding shard through 'slots' array.
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*
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* Column must have integer type.
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* T is type of column elements.
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*/
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template <typename T>
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IColumn::Selector createBlockSelector(
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const IColumn & column,
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size_t num_shards,
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const std::vector<size_t> & slots);
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}
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