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#pragma once
#include <Core/Types.h>
#include <Common/HashTable/Hash.h>
#include <Common/CacheBase.h>
#include <Common/SipHash.h>
#include <Common/ProfileEvents.h>
#include <IO/MMappedFile.h>
namespace ProfileEvents
{
extern const Event MMappedFileCacheHits;
extern const Event MMappedFileCacheMisses;
}
namespace DB
{
/** Cache of opened and mmapped files for reading.
* mmap/munmap is heavy operation and better to keep mapped file to subsequent use than to map/unmap every time.
*/
class MMappedFileCache : public CacheBase<UInt128, MMappedFile, UInt128TrivialHash>
{
private:
using Base = CacheBase<UInt128, MMappedFile, UInt128TrivialHash>;
public:
explicit MMappedFileCache(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, ssize_t length = -1)
{
SipHash hash;
hash.update(path_to_file.data(), path_to_file.size() + 1);
hash.update(offset);
hash.update(length);
return hash.get128();
}
template <typename LoadFunc>
MappedPtr getOrSet(const Key & key, LoadFunc && load)
{
auto result = Base::getOrSet(key, load);
if (result.second)
ProfileEvents::increment(ProfileEvents::MMappedFileCacheMisses);
else
ProfileEvents::increment(ProfileEvents::MMappedFileCacheHits);
return result.first;
}
};
using MMappedFileCachePtr = std::shared_ptr<MMappedFileCache>;
}
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