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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
#pragma once
#include <stdint.h>
#include <memory>
#include <string>
#include "rocksdb/cache.h"
#include "rocksdb/env.h"
#include "rocksdb/slice.h"
#include "rocksdb/statistics.h"
#include "rocksdb/status.h"
namespace rocksdb {
class SimCache;
// For instrumentation purpose, use NewSimCache instead of NewLRUCache API
// NewSimCache is a wrapper function returning a SimCache instance that can
// have additional interface provided in Simcache class besides Cache interface
// to predict block cache hit rate without actually allocating the memory. It
// can help users tune their current block cache size, and determine how
// efficient they are using the memory.
// Since GetSimCapacity() returns the capacity for simulutation, it differs from
// actual memory usage, which can be estimated as:
// sim_capacity * entry_size / (entry_size + block_size),
// where 76 <= entry_size <= 104,
// BlockBasedTableOptions.block_size = 4096 by default but is configurable,
// Therefore, generally the actual memory overhead of SimCache is Less than
// sim_capacity * 2%
extern std::shared_ptr<SimCache> NewSimCache(std::shared_ptr<Cache> cache,
size_t sim_capacity,
int num_shard_bits);
class SimCache : public Cache {
SimCache() {}
~SimCache() override {}
const char* Name() const override { return "SimCache"; }
// returns the maximum configured capacity of the simcache for simulation
virtual size_t GetSimCapacity() const = 0;
// simcache doesn't provide internal handler reference to user, so always
// PinnedUsage = 0 and the behavior will be not exactly consistent the
// with real cache.
// returns the memory size for the entries residing in the simcache.
virtual size_t GetSimUsage() const = 0;
// sets the maximum configured capacity of the simcache. When the new
// capacity is less than the old capacity and the existing usage is
// greater than new capacity, the implementation will purge old entries
// to fit new capapicty.
virtual void SetSimCapacity(size_t capacity) = 0;
// returns the lookup times of simcache
virtual uint64_t get_miss_counter() const = 0;
// returns the hit times of simcache
virtual uint64_t get_hit_counter() const = 0;
// reset the lookup and hit counters
virtual void reset_counter() = 0;
// String representation of the statistics of the simcache
virtual std::string ToString() const = 0;
// Start storing logs of the cache activity (Add/Lookup) into
// a file located at activity_log_file, max_logging_size option can be used to
// stop logging to the file automatically after reaching a specific size in
// bytes, a values of 0 disable this feature
virtual Status StartActivityLogging(const std::string& activity_log_file,
Env* env, uint64_t max_logging_size = 0) = 0;
// Stop cache activity logging if any
virtual void StopActivityLogging() = 0;
// Status of cache logging happening in background
virtual Status GetActivityLoggingStatus() = 0;
SimCache(const SimCache&);
SimCache& operator=(const SimCache&);
} // namespace rocksdb