ClickHouse/dbms/include/DB/Storages/MergeTree/LevelMergeSelector.h
2016-10-31 22:32:08 +03:00

45 lines
1.1 KiB
C++

#pragma once
#include <DB/Storages/MergeTree/MergeSelector.h>
namespace DB
{
/** Select parts to merge based on its level.
*
* Select first range of parts at least min_parts_to_merge length with minimum level.
*
* If enough time has passed, lower min_parts_to_merge.
* And if no ranges of consecutive parts with same level, and much time has passed,
* allow to select parts of different level.
* This is done to allow further merging when table is not updated.
*/
class LevelMergeSelector : public IMergeSelector
{
public:
struct Settings
{
size_t min_parts_to_merge = 8;
size_t max_parts_to_merge = 100;
/** min_parts_to_merge will be lowered by 1 after that time.
* It will be lowered by 2 after that time * 2^1,
* It will be lowered by 3 after that time * 2^2,
* and so on, exponentially.
*/
time_t lower_base_after = 300;
};
LevelMergeSelector(const Settings & settings) : settings(settings) {}
PartsInPartition select(
const Partitions & partitions,
const size_t max_total_size_to_merge) override;
private:
const Settings settings;
};
}