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105 lines
2.3 KiB
C++
105 lines
2.3 KiB
C++
#pragma once
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#include <vector>
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#include <Poco/SharedPtr.h>
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#include <Poco/Mutex.h>
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#include <DB/Common/SipHash.h>
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#include <DB/Common/ProfileEvents.h>
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#include <DB/IO/BufferWithOwnMemory.h>
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#include <DB/Interpreters/AggregationCommon.h>
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namespace DB
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{
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/** Кэш разжатых блоков для CachedCompressedReadBuffer. thread-safe.
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* NOTE Использовать LRU вместо простой кэш-таблицы.
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*/
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class UncompressedCache
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{
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public:
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struct Cell
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{
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UInt128 key;
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Memory data;
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size_t compressed_size;
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Cell() { key.first = 0; key.second = 0; compressed_size = 0; }
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};
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/// В ячейках кэш-таблицы лежат SharedPtr-ы на разжатые блоки. Это нужно, чтобы можно было достать ячейку, захватив владение ею.
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typedef Poco::SharedPtr<Cell> CellPtr;
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typedef std::vector<CellPtr> Cells;
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private:
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size_t num_cells;
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Cells cells;
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mutable Poco::FastMutex mutex;
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mutable size_t hits;
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mutable size_t misses;
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public:
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UncompressedCache(size_t num_cells_)
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: num_cells(num_cells_), cells(num_cells), hits(0), misses(0)
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{
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}
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/// Посчитать ключ от пути к файлу и смещения.
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static UInt128 hash(const String & path_to_file, size_t offset)
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{
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UInt128 key;
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SipHash hash;
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hash.update(path_to_file.data(), path_to_file.size() + 1);
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hash.update(reinterpret_cast<const char *>(&offset), sizeof(offset));
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hash.get128(key.first, key.second);
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return key;
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}
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CellPtr get(UInt128 key) const
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{
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Poco::ScopedLock<Poco::FastMutex> lock(mutex);
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CellPtr cell = cells[key.first % num_cells];
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if (cell && cell->key == key)
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{
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ProfileEvents::increment(ProfileEvents::UncompressedCacheHits);
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++hits;
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return cell;
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}
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else
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{
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ProfileEvents::increment(ProfileEvents::UncompressedCacheMisses);
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++misses;
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return NULL;
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}
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}
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void set(const CellPtr & new_cell)
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{
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Poco::ScopedLock<Poco::FastMutex> lock(mutex);
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CellPtr & cell = cells[new_cell->key.first % num_cells];
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if (!cell || cell->key != new_cell->key)
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cell = new_cell;
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}
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void getStats(size_t & out_hits, size_t & out_misses) const volatile
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{
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/// Синхронизация не нужна.
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out_hits = hits;
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out_misses = misses;
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}
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};
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typedef Poco::SharedPtr<UncompressedCache> UncompressedCachePtr;
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}
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