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rocksdb/cache/lru_secondary_cache.cc

169 lines
6.0 KiB

Add a secondary cache implementation based on LRUCache 1 (#9518) 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
3 years ago
// 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).
#include "cache/lru_secondary_cache.h"
#include <memory>
#include "memory/memory_allocator.h"
#include "util/compression.h"
#include "util/string_util.h"
namespace ROCKSDB_NAMESPACE {
namespace {
void DeletionCallback(const Slice& /*key*/, void* obj) {
delete reinterpret_cast<CacheAllocationPtr*>(obj);
obj = nullptr;
}
} // namespace
LRUSecondaryCache::LRUSecondaryCache(
size_t capacity, int num_shard_bits, bool strict_capacity_limit,
double high_pri_pool_ratio,
std::shared_ptr<MemoryAllocator> memory_allocator, bool use_adaptive_mutex,
CacheMetadataChargePolicy metadata_charge_policy,
CompressionType compression_type, uint32_t compress_format_version)
: cache_options_(capacity, num_shard_bits, strict_capacity_limit,
high_pri_pool_ratio, memory_allocator, use_adaptive_mutex,
metadata_charge_policy, compression_type,
compress_format_version) {
cache_ = NewLRUCache(capacity, num_shard_bits, strict_capacity_limit,
high_pri_pool_ratio, memory_allocator,
use_adaptive_mutex, metadata_charge_policy);
}
LRUSecondaryCache::~LRUSecondaryCache() { cache_.reset(); }
std::unique_ptr<SecondaryCacheResultHandle> LRUSecondaryCache::Lookup(
const Slice& key, const Cache::CreateCallback& create_cb, bool /*wait*/) {
std::unique_ptr<SecondaryCacheResultHandle> handle;
Cache::Handle* lru_handle = cache_->Lookup(key);
if (lru_handle == nullptr) {
return handle;
}
CacheAllocationPtr* ptr =
reinterpret_cast<CacheAllocationPtr*>(cache_->Value(lru_handle));
void* value = nullptr;
size_t charge = 0;
Status s;
if (cache_options_.compression_type == kNoCompression) {
s = create_cb(ptr->get(), cache_->GetCharge(lru_handle), &value, &charge);
} else {
UncompressionContext uncompression_context(cache_options_.compression_type);
UncompressionInfo uncompression_info(uncompression_context,
UncompressionDict::GetEmptyDict(),
cache_options_.compression_type);
size_t uncompressed_size = 0;
CacheAllocationPtr uncompressed;
uncompressed = UncompressData(
uncompression_info, (char*)ptr->get(), cache_->GetCharge(lru_handle),
&uncompressed_size, cache_options_.compress_format_version,
cache_options_.memory_allocator.get());
if (!uncompressed) {
cache_->Release(lru_handle, true);
return handle;
}
s = create_cb(uncompressed.get(), uncompressed_size, &value, &charge);
}
if (!s.ok()) {
cache_->Release(lru_handle, true);
return handle;
}
handle.reset(new LRUSecondaryCacheResultHandle(value, charge));
cache_->Release(lru_handle);
return handle;
}
Status LRUSecondaryCache::Insert(const Slice& key, void* value,
const Cache::CacheItemHelper* helper) {
size_t size = (*helper->size_cb)(value);
CacheAllocationPtr ptr =
AllocateBlock(size, cache_options_.memory_allocator.get());
Status s = (*helper->saveto_cb)(value, 0, size, ptr.get());
if (!s.ok()) {
return s;
}
Slice val(ptr.get(), size);
std::string compressed_val;
if (cache_options_.compression_type != kNoCompression) {
CompressionOptions compression_opts;
CompressionContext compression_context(cache_options_.compression_type);
uint64_t sample_for_compression = 0;
CompressionInfo compression_info(
compression_opts, compression_context, CompressionDict::GetEmptyDict(),
cache_options_.compression_type, sample_for_compression);
bool success =
CompressData(val, compression_info,
cache_options_.compress_format_version, &compressed_val);
if (!success) {
return Status::Corruption("Error compressing value.");
}
val = Slice(compressed_val);
size = compressed_val.size();
ptr = AllocateBlock(size, cache_options_.memory_allocator.get());
memcpy(ptr.get(), compressed_val.data(), size);
}
CacheAllocationPtr* buf = new CacheAllocationPtr(std::move(ptr));
return cache_->Insert(key, buf, size, DeletionCallback);
}
void LRUSecondaryCache::Erase(const Slice& key) { cache_->Erase(key); }
std::string LRUSecondaryCache::GetPrintableOptions() const {
std::string ret;
ret.reserve(20000);
const int kBufferSize = 200;
char buffer[kBufferSize];
ret.append(cache_->GetPrintableOptions());
snprintf(buffer, kBufferSize, " compression_type : %s\n",
CompressionTypeToString(cache_options_.compression_type).c_str());
ret.append(buffer);
snprintf(buffer, kBufferSize, " compression_type : %d\n",
cache_options_.compress_format_version);
ret.append(buffer);
return ret;
}
std::shared_ptr<SecondaryCache> NewLRUSecondaryCache(
size_t capacity, int num_shard_bits, bool strict_capacity_limit,
double high_pri_pool_ratio,
std::shared_ptr<MemoryAllocator> memory_allocator, bool use_adaptive_mutex,
CacheMetadataChargePolicy metadata_charge_policy,
CompressionType compression_type, uint32_t compress_format_version) {
return std::make_shared<LRUSecondaryCache>(
capacity, num_shard_bits, strict_capacity_limit, high_pri_pool_ratio,
memory_allocator, use_adaptive_mutex, metadata_charge_policy,
compression_type, compress_format_version);
}
std::shared_ptr<SecondaryCache> NewLRUSecondaryCache(
const LRUSecondaryCacheOptions& opts) {
// The secondary_cache is disabled for this LRUCache instance.
assert(opts.secondary_cache == nullptr);
return NewLRUSecondaryCache(
opts.capacity, opts.num_shard_bits, opts.strict_capacity_limit,
opts.high_pri_pool_ratio, opts.memory_allocator, opts.use_adaptive_mutex,
opts.metadata_charge_policy, opts.compression_type,
opts.compress_format_version);
}
} // namespace ROCKSDB_NAMESPACE