ClickHouse/dbms/IO/UncompressedCache.h

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#pragma once
#include <Common/LRUCache.h>
#include <Common/SipHash.h>
#include <Common/UInt128.h>
#include <Common/ProfileEvents.h>
#include <IO/BufferWithOwnMemory.h>
namespace ProfileEvents
{
extern const Event UncompressedCacheHits;
extern const Event UncompressedCacheMisses;
extern const Event UncompressedCacheWeightLost;
}
namespace DB
{
struct UncompressedCacheCell
{
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Memory<> data;
size_t compressed_size;
UInt32 additional_bytes;
};
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struct UncompressedSizeWeightFunction
{
size_t operator()(const UncompressedCacheCell & x) const
{
return x.data.size();
}
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};
/** Cache of decompressed blocks for implementation of CachedCompressedReadBuffer. thread-safe.
*/
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class UncompressedCache : public LRUCache<UInt128, UncompressedCacheCell, UInt128TrivialHash, UncompressedSizeWeightFunction>
{
private:
using Base = LRUCache<UInt128, UncompressedCacheCell, UInt128TrivialHash, UncompressedSizeWeightFunction>;
public:
UncompressedCache(size_t max_size_in_bytes)
: Base(max_size_in_bytes) {}
/// Calculate key from path to file and offset.
static UInt128 hash(const String & path_to_file, size_t offset)
{
UInt128 key;
SipHash hash;
hash.update(path_to_file.data(), path_to_file.size() + 1);
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hash.update(offset);
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hash.get128(key.low, key.high);
return key;
}
MappedPtr get(const Key & key)
{
MappedPtr res = Base::get(key);
if (res)
ProfileEvents::increment(ProfileEvents::UncompressedCacheHits);
else
ProfileEvents::increment(ProfileEvents::UncompressedCacheMisses);
return res;
}
private:
void onRemoveOverflowWeightLoss(size_t weight_loss) override
{
ProfileEvents::increment(ProfileEvents::UncompressedCacheWeightLost, weight_loss);
}
};
using UncompressedCachePtr = std::shared_ptr<UncompressedCache>;
}