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rocksdb/db/blob/blob_source.h

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// 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).
#pragma once
#include <cinttypes>
#include "cache/cache_helpers.h"
#include "cache/cache_key.h"
#include "db/blob/blob_file_cache.h"
#include "db/blob/blob_read_request.h"
#include "rocksdb/cache.h"
#include "rocksdb/rocksdb_namespace.h"
#include "table/block_based/cachable_entry.h"
#include "util/autovector.h"
namespace ROCKSDB_NAMESPACE {
struct ImmutableOptions;
class Status;
class FilePrefetchBuffer;
class Slice;
// BlobSource is a class that provides universal access to blobs, regardless of
// whether they are in the blob cache, secondary cache, or (remote) storage.
// Depending on user settings, it always fetch blobs from multi-tier cache and
// storage with minimal cost.
class BlobSource {
public:
BlobSource(const ImmutableOptions* immutable_options,
const std::string& db_id, const std::string& db_session_id,
BlobFileCache* blob_file_cache);
BlobSource(const BlobSource&) = delete;
BlobSource& operator=(const BlobSource&) = delete;
~BlobSource();
// Read a blob from the underlying cache or one blob file.
//
// If successful, returns ok and sets "*value" to the newly retrieved
// uncompressed blob. If there was an error while fetching the blob, sets
// "*value" to empty and returns a non-ok status.
//
// Note: For consistency, whether the blob is found in the cache or on disk,
// sets "*bytes_read" to the size of on-disk (possibly compressed) blob
// record.
Status GetBlob(const ReadOptions& read_options, const Slice& user_key,
uint64_t file_number, uint64_t offset, uint64_t file_size,
uint64_t value_size, CompressionType compression_type,
FilePrefetchBuffer* prefetch_buffer, PinnableSlice* value,
uint64_t* bytes_read);
// Read multiple blobs from the underlying cache or blob file(s).
//
// If successful, returns ok and sets "result" in the elements of "blob_reqs"
// to the newly retrieved uncompressed blobs. If there was an error while
// fetching one of blobs, sets its "result" to empty and sets its
// corresponding "status" to a non-ok status.
//
// Note:
// - The main difference between this function and MultiGetBlobFromOneFile is
// that this function can read multiple blobs from multiple blob files.
//
// - For consistency, whether the blob is found in the cache or on disk, sets
// "*bytes_read" to the total size of on-disk (possibly compressed) blob
// records.
void MultiGetBlob(const ReadOptions& read_options,
autovector<BlobFileReadRequests>& blob_reqs,
uint64_t* bytes_read);
// Read multiple blobs from the underlying cache or one blob file.
//
// If successful, returns ok and sets "result" in the elements of "blob_reqs"
// to the newly retrieved uncompressed blobs. If there was an error while
// fetching one of blobs, sets its "result" to empty and sets its
// corresponding "status" to a non-ok status.
//
// Note:
// - The main difference between this function and MultiGetBlob is that this
// function is only used for the case where the demanded blobs are stored in
// one blob file. MultiGetBlob will call this function multiple times if the
// demanded blobs are stored in multiple blob files.
//
// - For consistency, whether the blob is found in the cache or on disk, sets
// "*bytes_read" to the total size of on-disk (possibly compressed) blob
// records.
void MultiGetBlobFromOneFile(const ReadOptions& read_options,
uint64_t file_number, uint64_t file_size,
autovector<BlobReadRequest>& blob_reqs,
uint64_t* bytes_read);
inline Status GetBlobFileReader(
uint64_t blob_file_number,
CacheHandleGuard<BlobFileReader>* blob_file_reader) {
return blob_file_cache_->GetBlobFileReader(blob_file_number,
blob_file_reader);
}
inline Cache* GetBlobCache() const { return blob_cache_.get(); }
bool TEST_BlobInCache(uint64_t file_number, uint64_t file_size,
uint64_t offset) const;
private:
Status GetBlobFromCache(const Slice& cache_key,
CacheHandleGuard<std::string>* blob) const;
Status PutBlobIntoCache(const Slice& cache_key,
CacheHandleGuard<std::string>* cached_blob,
PinnableSlice* blob) const;
Cache::Handle* GetEntryFromCache(const Slice& key) const;
Status InsertEntryIntoCache(const Slice& key, std::string* value,
size_t charge, Cache::Handle** cache_handle,
Cache::Priority priority) const;
inline CacheKey GetCacheKey(uint64_t file_number, uint64_t file_size,
uint64_t offset) const {
OffsetableCacheKey base_cache_key(db_id_, db_session_id_, file_number,
file_size);
return base_cache_key.WithOffset(offset);
}
// Callbacks for secondary blob cache
static size_t SizeCallback(void* obj);
static Status SaveToCallback(void* from_obj, size_t from_offset,
size_t length, void* out);
static Cache::CacheItemHelper* GetCacheItemHelper();
const std::string& db_id_;
const std::string& db_session_id_;
Statistics* statistics_;
// A cache to store blob file reader.
BlobFileCache* blob_file_cache_;
// A cache to store uncompressed blobs.
std::shared_ptr<Cache> blob_cache_;
// The control option of how the cache tiers will be used. Currently rocksdb
// support block/blob cache (volatile tier) and secondary cache (this tier
// isn't strictly speaking a non-volatile tier since the compressed cache in
// this tier is in volatile memory).
const CacheTier lowest_used_cache_tier_;
};
} // namespace ROCKSDB_NAMESPACE