f706a9c199
Summary: **Summary:** RocksDB uses a block cache to reduce IO and make queries more efficient. The block cache is based on the LRU algorithm (LRUCache) and keeps objects containing uncompressed data, such as Block, ParsedFullFilterBlock etc. It allows the user to configure a second level cache (rocksdb::SecondaryCache) to extend the primary block cache by holding items evicted from it. Some of the major RocksDB users, like MyRocks, use direct IO and would like to use a primary block cache for uncompressed data and a secondary cache for compressed data. The latter allows us to mitigate the loss of the Linux page cache due to direct IO. This PR includes a concrete implementation of rocksdb::SecondaryCache that integrates with compression libraries such as LZ4 and implements an LRU cache to hold compressed blocks. Pull Request resolved: https://github.com/facebook/rocksdb/pull/9518 Test Plan: In this PR, the lru_secondary_cache_test.cc includes the following tests: 1. The unit tests for the secondary cache with either compression or no compression, such as basic tests, fails tests. 2. The integration tests with both primary cache and this secondary cache . **Follow Up:** 1. Statistics (e.g. compression ratio) will be added in another PR. 2. Once this implementation is ready, I will do some shadow testing and benchmarking with UDB to measure the impact. Reviewed By: anand1976 Differential Revision: D34430930 Pulled By: gitbw95 fbshipit-source-id: 218d78b672a2f914856d8a90ff32f2f5b5043ded
86 lines
2.7 KiB
C++
86 lines
2.7 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once
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#include <memory>
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#include "cache/lru_cache.h"
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#include "memory/memory_allocator.h"
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#include "rocksdb/secondary_cache.h"
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#include "rocksdb/slice.h"
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#include "rocksdb/status.h"
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#include "util/compression.h"
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namespace ROCKSDB_NAMESPACE {
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class LRUSecondaryCacheResultHandle : public SecondaryCacheResultHandle {
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public:
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LRUSecondaryCacheResultHandle(void* value, size_t size)
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: value_(value), size_(size) {}
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virtual ~LRUSecondaryCacheResultHandle() override = default;
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LRUSecondaryCacheResultHandle(const LRUSecondaryCacheResultHandle&) = delete;
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LRUSecondaryCacheResultHandle& operator=(
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const LRUSecondaryCacheResultHandle&) = delete;
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bool IsReady() override { return true; }
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void Wait() override {}
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void* Value() override { return value_; }
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size_t Size() override { return size_; }
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private:
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void* value_;
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size_t size_;
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};
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// The LRUSecondaryCache is a concrete implementation of
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// rocksdb::SecondaryCache.
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//
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// Users can also cast a pointer to it and call methods on
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// it directly, especially custom methods that may be added
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// in the future. For example -
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// std::unique_ptr<rocksdb::SecondaryCache> cache =
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// NewLRUSecondaryCache(opts);
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// static_cast<LRUSecondaryCache*>(cache.get())->Erase(key);
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class LRUSecondaryCache : public SecondaryCache {
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public:
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LRUSecondaryCache(
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size_t capacity, int num_shard_bits, bool strict_capacity_limit,
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double high_pri_pool_ratio,
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std::shared_ptr<MemoryAllocator> memory_allocator = nullptr,
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bool use_adaptive_mutex = kDefaultToAdaptiveMutex,
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CacheMetadataChargePolicy metadata_charge_policy =
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kDontChargeCacheMetadata,
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CompressionType compression_type = CompressionType::kLZ4Compression,
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uint32_t compress_format_version = 2);
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virtual ~LRUSecondaryCache() override;
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const char* Name() const override { return "LRUSecondaryCache"; }
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Status Insert(const Slice& key, void* value,
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const Cache::CacheItemHelper* helper) override;
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std::unique_ptr<SecondaryCacheResultHandle> Lookup(
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const Slice& key, const Cache::CreateCallback& create_cb,
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bool /*wait*/) override;
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void Erase(const Slice& key) override;
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void WaitAll(std::vector<SecondaryCacheResultHandle*> /*handles*/) override {}
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std::string GetPrintableOptions() const override;
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private:
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std::shared_ptr<Cache> cache_;
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LRUSecondaryCacheOptions cache_options_;
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};
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} // namespace ROCKSDB_NAMESPACE
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