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#pragma once
#include <cstddef>
#include <ctime>
#include <vector>
#include <functional>
#include <Storages/MergeTree/MergeTreeDataPartTTLInfo.h>
#include <Parsers/IAST_fwd.h>
namespace DB
{
class IMergeTreeDataPart;
/** Interface of algorithm to select data parts to merge
* (merge is also known as "compaction").
* Following properties depend on it:
*
* 1. Number of data parts at some moment in time.
* If parts are merged frequently, then data will be represented by lower number of parts, in average,
* but with cost of higher write amplification.
*
* 2. Write amplification ratio: how much times, on average, source data was written
* (during initial writes and followed merges).
*
* Number of parallel merges are controlled outside of scope of this interface.
*/
class IMergeSelector
{
using DataPartPtr = std::shared_ptr<const IMergeTreeDataPart>;
public:
/// Information about data part relevant to merge selecting strategy.
struct Part
{
/// Size of data part in bytes.
size_t size = 0;
/// How old this data part in seconds.
time_t age = 0;
/// Depth of tree of merges by which this part was created. New parts has zero level.
unsigned level = 0;
/// Opaque pointer to avoid dependencies (it is not possible to do forward declaration of typedef).
const void * data = nullptr;
/// Information about different TTLs for part. Can be used by
/// TTLSelector to assign merges with TTL.
const MergeTreeDataPartTTLInfos * ttl_infos = nullptr;
/// Part compression codec definition.
ASTPtr compression_codec_desc;
bool shall_participate_in_merges = true;
const DataPartPtr & getDataPartPtr() const
{
return *static_cast<const DataPartPtr *>(data);
}
};
/// Parts are belong to partitions. Only parts within same partition could be merged.
using PartsRange = std::vector<Part>;
/// Parts are in some specific order. Parts could be merged only in contiguous ranges.
using PartsRanges = std::vector<PartsRange>;
/** Function could be called at any frequency and it must decide, should you do any merge at all.
* If better not to do any merge, it returns empty result.
*/
virtual PartsRange select(
const PartsRanges & parts_ranges,
size_t max_total_size_to_merge) = 0;
virtual ~IMergeSelector() = default;
};
}
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