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67 lines
2.0 KiB
C++
67 lines
2.0 KiB
C++
#pragma once
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#include <cstddef>
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#include <ctime>
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#include <vector>
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#include <functional>
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namespace DB
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{
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/** Interface of algorithm to select data parts to merge
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* (merge is also known as "compaction").
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* Following properties depend on it:
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*
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* 1. Number of data parts at some moment in time.
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* If parts are merged frequently, then data will be represented by lower number of parts, in average,
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* but with cost of higher write amplification.
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*
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* 2. Write amplification ratio: how much times, on average, source data was written
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* (during initial writes and followed merges).
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*
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* Number of parallel merges are controlled outside of scope of this interface.
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*/
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class IMergeSelector
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{
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public:
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/// Information about data part relevant to merge selecting strategy.
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struct Part
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{
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/// Size of data part in bytes.
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size_t size;
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/// How old this data part in seconds.
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time_t age;
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/// Depth of tree of merges by which this part was created. New parts has zero level.
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unsigned level;
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/// Opaque pointer to avoid dependencies (it is not possible to do forward declaration of typedef).
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const void * data;
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/// Minimal time, when we need to delete some data from this part.
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time_t min_ttl;
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/// Maximum time, when we will need to drop this part altogether because all rows in it are expired.
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time_t max_ttl;
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};
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/// Parts are belong to partitions. Only parts within same partition could be merged.
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using PartsInPartition = std::vector<Part>;
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/// Parts are in some specific order. Parts could be merged only in contiguous ranges.
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using Partitions = std::vector<PartsInPartition>;
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/** Function could be called at any frequency and it must decide, should you do any merge at all.
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* If better not to do any merge, it returns empty result.
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*/
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virtual PartsInPartition select(
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const Partitions & partitions,
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const size_t max_total_size_to_merge) = 0;
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virtual ~IMergeSelector() {}
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};
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}
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