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Introduce a dedicated class to represent blob values (facebook#10571)
Summary: The patch introduces a new class called `BlobContents`, which represents a single uncompressed blob value. We currently use `std::string` for this purpose; `BlobContents` is somewhat smaller but the primary reason for a dedicated class is that it enables certain improvements and optimizations like eliding a copy when inserting a blob into the cache, using custom allocators, or more control over and better accounting of the memory usage of cached blobs (see facebook#10484). (We plan to implement these in subsequent PRs.) Pull Request resolved: facebook#10571 Test Plan: `make check` Reviewed By: riversand963 Differential Revision: D39000965 Pulled By: ltamasi fbshipit-source-id: f296eddf9dec4fc3e11cad525b462bdf63c78f96
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,63 @@ | ||
| // Copyright (c) Meta Platforms, Inc. and affiliates. | ||
| // 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). | ||
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| #include "db/blob/blob_contents.h" | ||
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| #include <cassert> | ||
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| #include "cache/cache_helpers.h" | ||
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| namespace ROCKSDB_NAMESPACE { | ||
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| std::unique_ptr<BlobContents> BlobContents::Create( | ||
| CacheAllocationPtr&& allocation, size_t size) { | ||
| return std::unique_ptr<BlobContents>( | ||
| new BlobContents(std::move(allocation), size)); | ||
| } | ||
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| size_t BlobContents::SizeCallback(void* obj) { | ||
| assert(obj); | ||
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| return static_cast<const BlobContents*>(obj)->size(); | ||
| } | ||
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| Status BlobContents::SaveToCallback(void* from_obj, size_t from_offset, | ||
| size_t length, void* out) { | ||
| assert(from_obj); | ||
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| const BlobContents* buf = static_cast<const BlobContents*>(from_obj); | ||
| assert(buf->size() >= from_offset + length); | ||
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| memcpy(out, buf->data().data() + from_offset, length); | ||
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| return Status::OK(); | ||
| } | ||
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| void BlobContents::DeleteCallback(const Slice& key, void* value) { | ||
| DeleteCacheEntry<BlobContents>(key, value); | ||
| } | ||
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| Cache::CacheItemHelper* BlobContents::GetCacheItemHelper() { | ||
| static Cache::CacheItemHelper cache_helper(&SizeCallback, &SaveToCallback, | ||
| &DeleteCallback); | ||
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| return &cache_helper; | ||
| } | ||
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| Status BlobContents::CreateCallback(const void* buf, size_t size, | ||
| void** out_obj, size_t* charge) { | ||
| CacheAllocationPtr allocation(new char[size]); | ||
| memcpy(allocation.get(), buf, size); | ||
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| std::unique_ptr<BlobContents> obj = Create(std::move(allocation), size); | ||
| BlobContents* const contents = obj.release(); | ||
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| *out_obj = contents; | ||
| *charge = contents->size(); | ||
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| return Status::OK(); | ||
| } | ||
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| } // namespace ROCKSDB_NAMESPACE |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,56 @@ | ||
| // Copyright (c) Meta Platforms, Inc. and affiliates. | ||
| // 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). | ||
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| #pragma once | ||
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| #include <memory> | ||
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| #include "memory/memory_allocator.h" | ||
| #include "rocksdb/cache.h" | ||
| #include "rocksdb/rocksdb_namespace.h" | ||
| #include "rocksdb/slice.h" | ||
| #include "rocksdb/status.h" | ||
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| namespace ROCKSDB_NAMESPACE { | ||
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| // A class representing a single uncompressed value read from a blob file. | ||
| class BlobContents { | ||
| public: | ||
| static std::unique_ptr<BlobContents> Create(CacheAllocationPtr&& allocation, | ||
| size_t size); | ||
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| BlobContents(const BlobContents&) = delete; | ||
| BlobContents& operator=(const BlobContents&) = delete; | ||
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| BlobContents(BlobContents&&) = default; | ||
| BlobContents& operator=(BlobContents&&) = default; | ||
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| ~BlobContents() = default; | ||
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| const Slice& data() const { return data_; } | ||
| size_t size() const { return data_.size(); } | ||
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| // Callbacks for secondary cache | ||
| static size_t SizeCallback(void* obj); | ||
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| static Status SaveToCallback(void* from_obj, size_t from_offset, | ||
| size_t length, void* out); | ||
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| static void DeleteCallback(const Slice& key, void* value); | ||
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| static Cache::CacheItemHelper* GetCacheItemHelper(); | ||
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| static Status CreateCallback(const void* buf, size_t size, void** out_obj, | ||
| size_t* charge); | ||
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| private: | ||
| BlobContents(CacheAllocationPtr&& allocation, size_t size) | ||
| : allocation_(std::move(allocation)), data_(allocation_.get(), size) {} | ||
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| CacheAllocationPtr allocation_; | ||
| Slice data_; | ||
| }; | ||
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| } // namespace ROCKSDB_NAMESPACE |
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