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rocksdb/table/block_based/block_based_table_reader.h

691 lines
30 KiB

// 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).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include "db/range_tombstone_fragmenter.h"
#include "file/filename.h"
#include "table/block_based/block_based_table_factory.h"
#include "table/block_based/block_type.h"
#include "table/block_based/cachable_entry.h"
#include "table/block_based/filter_block.h"
#include "table/block_based/uncompression_dict_reader.h"
#include "table/table_properties_internal.h"
#include "table/table_reader.h"
#include "table/two_level_iterator.h"
#include "trace_replay/block_cache_tracer.h"
namespace ROCKSDB_NAMESPACE {
class Cache;
class FilterBlockReader;
class BlockBasedFilterBlockReader;
class FullFilterBlockReader;
class Footer;
class InternalKeyComparator;
class Iterator;
class FSRandomAccessFile;
class TableCache;
class TableReader;
class WritableFile;
struct BlockBasedTableOptions;
struct EnvOptions;
struct ReadOptions;
class GetContext;
typedef std::vector<std::pair<std::string, std::string>> KVPairBlock;
// Reader class for BlockBasedTable format.
// For the format of BlockBasedTable refer to
// https://github.com/facebook/rocksdb/wiki/Rocksdb-BlockBasedTable-Format.
// This is the default table type. Data is chucked into fixed size blocks and
// each block in-turn stores entries. When storing data, we can compress and/or
// encode data efficiently within a block, which often results in a much smaller
// data size compared with the raw data size. As for the record retrieval, we'll
// first locate the block where target record may reside, then read the block to
// memory, and finally search that record within the block. Of course, to avoid
// frequent reads of the same block, we introduced the block cache to keep the
// loaded blocks in the memory.
class BlockBasedTable : public TableReader {
public:
static const std::string kFilterBlockPrefix;
static const std::string kFullFilterBlockPrefix;
static const std::string kPartitionedFilterBlockPrefix;
// The longest prefix of the cache key used to identify blocks.
// For Posix files the unique ID is three varints.
static const size_t kMaxCacheKeyPrefixSize = kMaxVarint64Length * 3 + 1;
// All the below fields control iterator readahead
static const size_t kInitAutoReadaheadSize = 8 * 1024;
static const int kMinNumFileReadsToStartAutoReadahead = 2;
// Attempt to open the table that is stored in bytes [0..file_size)
// of "file", and read the metadata entries necessary to allow
// retrieving data from the table.
//
// If successful, returns ok and sets "*table_reader" to the newly opened
// table. The client should delete "*table_reader" when no longer needed.
// If there was an error while initializing the table, sets "*table_reader"
// to nullptr and returns a non-ok status.
//
// @param file must remain live while this Table is in use.
// @param prefetch_index_and_filter_in_cache can be used to disable
// prefetching of
// index and filter blocks into block cache at startup
// @param skip_filters Disables loading/accessing the filter block. Overrides
// prefetch_index_and_filter_in_cache, so filter will be skipped if both
// are set.
// @param force_direct_prefetch if true, always prefetching to RocksDB
// buffer, rather than calling RandomAccessFile::Prefetch().
static Status Open(const ReadOptions& ro, const ImmutableCFOptions& ioptions,
const EnvOptions& env_options,
const BlockBasedTableOptions& table_options,
const InternalKeyComparator& internal_key_comparator,
std::unique_ptr<RandomAccessFileReader>&& file,
uint64_t file_size,
std::unique_ptr<TableReader>* table_reader,
const SliceTransform* prefix_extractor = nullptr,
bool prefetch_index_and_filter_in_cache = true,
bool skip_filters = false, int level = -1,
const bool immortal_table = false,
const SequenceNumber largest_seqno = 0,
bool force_direct_prefetch = false,
TailPrefetchStats* tail_prefetch_stats = nullptr,
BlockCacheTracer* const block_cache_tracer = nullptr,
size_t max_file_size_for_l0_meta_pin = 0);
bool PrefixMayMatch(const Slice& internal_key,
const ReadOptions& read_options,
const SliceTransform* options_prefix_extractor,
const bool need_upper_bound_check,
BlockCacheLookupContext* lookup_context) const;
// Returns a new iterator over the table contents.
// The result of NewIterator() is initially invalid (caller must
// call one of the Seek methods on the iterator before using it).
// @param read_options Must outlive the returned iterator.
// @param skip_filters Disables loading/accessing the filter block
// compaction_readahead_size: its value will only be used if caller =
// kCompaction.
InternalIterator* NewIterator(const ReadOptions&,
const SliceTransform* prefix_extractor,
Arena* arena, bool skip_filters,
TableReaderCaller caller,
size_t compaction_readahead_size = 0,
bool allow_unprepared_value = false) override;
FragmentedRangeTombstoneIterator* NewRangeTombstoneIterator(
const ReadOptions& read_options) override;
// @param skip_filters Disables loading/accessing the filter block
Status Get(const ReadOptions& readOptions, const Slice& key,
GetContext* get_context, const SliceTransform* prefix_extractor,
bool skip_filters = false) override;
void MultiGet(const ReadOptions& readOptions,
const MultiGetContext::Range* mget_range,
const SliceTransform* prefix_extractor,
bool skip_filters = false) override;
// Pre-fetch the disk blocks that correspond to the key range specified by
// (kbegin, kend). The call will return error status in the event of
// IO or iteration error.
Status Prefetch(const Slice* begin, const Slice* end) override;
// Given a key, return an approximate byte offset in the file where
// the data for that key begins (or would begin if the key were
// present in the file). The returned value is in terms of file
// bytes, and so includes effects like compression of the underlying data.
// E.g., the approximate offset of the last key in the table will
// be close to the file length.
uint64_t ApproximateOffsetOf(const Slice& key,
TableReaderCaller caller) override;
// Given start and end keys, return the approximate data size in the file
// between the keys. The returned value is in terms of file bytes, and so
// includes effects like compression of the underlying data.
// The start key must not be greater than the end key.
uint64_t ApproximateSize(const Slice& start, const Slice& end,
TableReaderCaller caller) override;
bool TEST_BlockInCache(const BlockHandle& handle) const;
// Returns true if the block for the specified key is in cache.
// REQUIRES: key is in this table && block cache enabled
bool TEST_KeyInCache(const ReadOptions& options, const Slice& key);
// Set up the table for Compaction. Might change some parameters with
// posix_fadvise
void SetupForCompaction() override;
std::shared_ptr<const TableProperties> GetTableProperties() const override;
size_t ApproximateMemoryUsage() const override;
// convert SST file to a human readable form
Status DumpTable(WritableFile* out_file) override;
Status VerifyChecksum(const ReadOptions& readOptions,
TableReaderCaller caller) override;
~BlockBasedTable();
bool TEST_FilterBlockInCache() const;
bool TEST_IndexBlockInCache() const;
// IndexReader is the interface that provides the functionality for index
// access.
class IndexReader {
public:
virtual ~IndexReader() = default;
// Create an iterator for index access. If iter is null, then a new object
// is created on the heap, and the callee will have the ownership.
// If a non-null iter is passed in, it will be used, and the returned value
// is either the same as iter or a new on-heap object that
// wraps the passed iter. In the latter case the return value points
// to a different object then iter, and the callee has the ownership of the
// returned object.
virtual InternalIteratorBase<IndexValue>* NewIterator(
const ReadOptions& read_options, bool disable_prefix_seek,
IndexBlockIter* iter, GetContext* get_context,
BlockCacheLookupContext* lookup_context) = 0;
// Report an approximation of how much memory has been used other than
// memory that was allocated in block cache.
virtual size_t ApproximateMemoryUsage() const = 0;
// Cache the dependencies of the index reader (e.g. the partitions
// of a partitioned index).
virtual Status CacheDependencies(const ReadOptions& /*ro*/,
bool /* pin */) {
return Status::OK();
}
};
class IndexReaderCommon;
static Slice GetCacheKey(const char* cache_key_prefix,
size_t cache_key_prefix_size,
const BlockHandle& handle, char* cache_key);
// Retrieve all key value pairs from data blocks in the table.
// The key retrieved are internal keys.
Status GetKVPairsFromDataBlocks(std::vector<KVPairBlock>* kv_pair_blocks);
struct Rep;
Rep* get_rep() { return rep_; }
const Rep* get_rep() const { return rep_; }
// input_iter: if it is not null, update this one and return it as Iterator
template <typename TBlockIter>
TBlockIter* NewDataBlockIterator(
const ReadOptions& ro, const BlockHandle& block_handle,
TBlockIter* input_iter, BlockType block_type, GetContext* get_context,
BlockCacheLookupContext* lookup_context, Status s,
FilePrefetchBuffer* prefetch_buffer, bool for_compaction = false) const;
// input_iter: if it is not null, update this one and return it as Iterator
template <typename TBlockIter>
TBlockIter* NewDataBlockIterator(const ReadOptions& ro,
CachableEntry<Block>& block,
TBlockIter* input_iter, Status s) const;
class PartitionedIndexIteratorState;
template <typename TBlocklike>
friend class FilterBlockReaderCommon;
friend class PartitionIndexReader;
friend class UncompressionDictReader;
protected:
Rep* rep_;
explicit BlockBasedTable(Rep* rep, BlockCacheTracer* const block_cache_tracer)
: rep_(rep), block_cache_tracer_(block_cache_tracer) {}
// No copying allowed
explicit BlockBasedTable(const TableReader&) = delete;
void operator=(const TableReader&) = delete;
private:
friend class MockedBlockBasedTable;
friend class BlockBasedTableReaderTestVerifyChecksum_ChecksumMismatch_Test;
static std::atomic<uint64_t> next_cache_key_id_;
BlockCacheTracer* const block_cache_tracer_;
void UpdateCacheHitMetrics(BlockType block_type, GetContext* get_context,
size_t usage) const;
void UpdateCacheMissMetrics(BlockType block_type,
GetContext* get_context) const;
void UpdateCacheInsertionMetrics(BlockType block_type,
GetContext* get_context, size_t usage,
bool redundant) const;
Cache::Handle* GetEntryFromCache(Cache* block_cache, const Slice& key,
BlockType block_type,
GetContext* get_context) const;
// Either Block::NewDataIterator() or Block::NewIndexIterator().
template <typename TBlockIter>
static TBlockIter* InitBlockIterator(const Rep* rep, Block* block,
BlockType block_type,
TBlockIter* input_iter,
bool block_contents_pinned);
// If block cache enabled (compressed or uncompressed), looks for the block
// identified by handle in (1) uncompressed cache, (2) compressed cache, and
// then (3) file. If found, inserts into the cache(s) that were searched
// unsuccessfully (e.g., if found in file, will add to both uncompressed and
// compressed caches if they're enabled).
//
// @param block_entry value is set to the uncompressed block if found. If
// in uncompressed block cache, also sets cache_handle to reference that
// block.
template <typename TBlocklike>
Status MaybeReadBlockAndLoadToCache(
FilePrefetchBuffer* prefetch_buffer, const ReadOptions& ro,
const BlockHandle& handle, const UncompressionDict& uncompression_dict,
CachableEntry<TBlocklike>* block_entry, BlockType block_type,
GetContext* get_context, BlockCacheLookupContext* lookup_context,
BlockContents* contents) const;
// Similar to the above, with one crucial difference: it will retrieve the
// block from the file even if there are no caches configured (assuming the
// read options allow I/O).
template <typename TBlocklike>
Status RetrieveBlock(FilePrefetchBuffer* prefetch_buffer,
const ReadOptions& ro, const BlockHandle& handle,
const UncompressionDict& uncompression_dict,
CachableEntry<TBlocklike>* block_entry,
BlockType block_type, GetContext* get_context,
BlockCacheLookupContext* lookup_context,
bool for_compaction, bool use_cache) const;
void RetrieveMultipleBlocks(
const ReadOptions& options, const MultiGetRange* batch,
const autovector<BlockHandle, MultiGetContext::MAX_BATCH_SIZE>* handles,
autovector<Status, MultiGetContext::MAX_BATCH_SIZE>* statuses,
autovector<CachableEntry<Block>, MultiGetContext::MAX_BATCH_SIZE>*
results,
char* scratch, const UncompressionDict& uncompression_dict) const;
// Get the iterator from the index reader.
//
// If input_iter is not set, return a new Iterator.
// If input_iter is set, try to update it and return it as Iterator.
// However note that in some cases the returned iterator may be different
// from input_iter. In such case the returned iterator should be freed.
//
// Note: ErrorIterator with Status::Incomplete shall be returned if all the
// following conditions are met:
// 1. We enabled table_options.cache_index_and_filter_blocks.
// 2. index is not present in block cache.
// 3. We disallowed any io to be performed, that is, read_options ==
// kBlockCacheTier
InternalIteratorBase<IndexValue>* NewIndexIterator(
const ReadOptions& read_options, bool need_upper_bound_check,
IndexBlockIter* input_iter, GetContext* get_context,
BlockCacheLookupContext* lookup_context) const;
// Read block cache from block caches (if set): block_cache and
// block_cache_compressed.
// On success, Status::OK with be returned and @block will be populated with
// pointer to the block as well as its block handle.
// @param uncompression_dict Data for presetting the compression library's
// dictionary.
template <typename TBlocklike>
Status GetDataBlockFromCache(
const Slice& block_cache_key, const Slice& compressed_block_cache_key,
Cache* block_cache, Cache* block_cache_compressed,
const ReadOptions& read_options, CachableEntry<TBlocklike>* block,
const UncompressionDict& uncompression_dict, BlockType block_type,
GetContext* get_context) const;
// Put a raw block (maybe compressed) to the corresponding block caches.
// This method will perform decompression against raw_block if needed and then
// populate the block caches.
// On success, Status::OK will be returned; also @block will be populated with
// uncompressed block and its cache handle.
//
// Allocated memory managed by raw_block_contents will be transferred to
// PutDataBlockToCache(). After the call, the object will be invalid.
// @param uncompression_dict Data for presetting the compression library's
// dictionary.
template <typename TBlocklike>
Status PutDataBlockToCache(const Slice& block_cache_key,
const Slice& compressed_block_cache_key,
Cache* block_cache, Cache* block_cache_compressed,
CachableEntry<TBlocklike>* cached_block,
BlockContents* raw_block_contents,
CompressionType raw_block_comp_type,
const UncompressionDict& uncompression_dict,
MemoryAllocator* memory_allocator,
BlockType block_type,
GetContext* get_context) const;
// Calls (*handle_result)(arg, ...) repeatedly, starting with the entry found
// after a call to Seek(key), until handle_result returns false.
// May not make such a call if filter policy says that key is not present.
friend class TableCache;
friend class BlockBasedTableBuilder;
// Create a index reader based on the index type stored in the table.
// Optionally, user can pass a preloaded meta_index_iter for the index that
// need to access extra meta blocks for index construction. This parameter
// helps avoid re-reading meta index block if caller already created one.
Status CreateIndexReader(const ReadOptions& ro,
FilePrefetchBuffer* prefetch_buffer,
InternalIterator* preloaded_meta_index_iter,
bool use_cache, bool prefetch, bool pin,
BlockCacheLookupContext* lookup_context,
std::unique_ptr<IndexReader>* index_reader);
bool FullFilterKeyMayMatch(const ReadOptions& read_options,
FilterBlockReader* filter, const Slice& user_key,
const bool no_io,
const SliceTransform* prefix_extractor,
GetContext* get_context,
BlockCacheLookupContext* lookup_context) const;
void FullFilterKeysMayMatch(const ReadOptions& read_options,
FilterBlockReader* filter, MultiGetRange* range,
const bool no_io,
const SliceTransform* prefix_extractor,
BlockCacheLookupContext* lookup_context) const;
// If force_direct_prefetch is true, always prefetching to RocksDB
// buffer, rather than calling RandomAccessFile::Prefetch().
static Status PrefetchTail(
const ReadOptions& ro, RandomAccessFileReader* file, uint64_t file_size,
bool force_direct_prefetch, TailPrefetchStats* tail_prefetch_stats,
const bool prefetch_all, const bool preload_all,
std::unique_ptr<FilePrefetchBuffer>* prefetch_buffer);
Status ReadMetaIndexBlock(const ReadOptions& ro,
FilePrefetchBuffer* prefetch_buffer,
std::unique_ptr<Block>* metaindex_block,
std::unique_ptr<InternalIterator>* iter);
Status TryReadPropertiesWithGlobalSeqno(const ReadOptions& ro,
FilePrefetchBuffer* prefetch_buffer,
const Slice& handle_value,
TableProperties** table_properties);
Status ReadPropertiesBlock(const ReadOptions& ro,
FilePrefetchBuffer* prefetch_buffer,
InternalIterator* meta_iter,
const SequenceNumber largest_seqno);
Status ReadRangeDelBlock(const ReadOptions& ro,
FilePrefetchBuffer* prefetch_buffer,
InternalIterator* meta_iter,
const InternalKeyComparator& internal_comparator,
BlockCacheLookupContext* lookup_context);
Status PrefetchIndexAndFilterBlocks(
const ReadOptions& ro, FilePrefetchBuffer* prefetch_buffer,
InternalIterator* meta_iter, BlockBasedTable* new_table,
bool prefetch_all, const BlockBasedTableOptions& table_options,
const int level, size_t file_size, size_t max_file_size_for_l0_meta_pin,
BlockCacheLookupContext* lookup_context);
static BlockType GetBlockTypeForMetaBlockByName(const Slice& meta_block_name);
Status VerifyChecksumInMetaBlocks(InternalIteratorBase<Slice>* index_iter);
Status VerifyChecksumInBlocks(const ReadOptions& read_options,
InternalIteratorBase<IndexValue>* index_iter);
// Create the filter from the filter block.
std::unique_ptr<FilterBlockReader> CreateFilterBlockReader(
const ReadOptions& ro, FilePrefetchBuffer* prefetch_buffer,
bool use_cache, bool prefetch, bool pin,
BlockCacheLookupContext* lookup_context);
static void SetupCacheKeyPrefix(Rep* rep);
// Generate a cache key prefix from the file
template <typename TCache, typename TFile>
static void GenerateCachePrefix(TCache* cc, TFile* file, char* buffer,
size_t* size) {
// generate an id from the file
*size = file->GetUniqueId(buffer, kMaxCacheKeyPrefixSize);
// If the prefix wasn't generated or was too long,
// create one from the cache.
if (cc != nullptr && *size == 0) {
char* end = EncodeVarint64(buffer, cc->NewId());
*size = static_cast<size_t>(end - buffer);
}
}
// Size of all data blocks, maybe approximate
uint64_t GetApproximateDataSize();
// Given an iterator return its offset in data block section of file.
uint64_t ApproximateDataOffsetOf(
const InternalIteratorBase<IndexValue>& index_iter,
uint64_t data_size) const;
// Helper functions for DumpTable()
Status DumpIndexBlock(std::ostream& out_stream);
Status DumpDataBlocks(std::ostream& out_stream);
void DumpKeyValue(const Slice& key, const Slice& value,
std::ostream& out_stream);
// A cumulative data block file read in MultiGet lower than this size will
// use a stack buffer
static constexpr size_t kMultiGetReadStackBufSize = 8192;
friend class PartitionedFilterBlockReader;
friend class PartitionedFilterBlockTest;
friend class DBBasicTest_MultiGetIOBufferOverrun_Test;
};
// Maintaining state of a two-level iteration on a partitioned index structure.
class BlockBasedTable::PartitionedIndexIteratorState
: public TwoLevelIteratorState {
public:
PartitionedIndexIteratorState(
const BlockBasedTable* table,
std::unordered_map<uint64_t, CachableEntry<Block>>* block_map);
InternalIteratorBase<IndexValue>* NewSecondaryIterator(
const BlockHandle& index_value) override;
private:
// Don't own table_
const BlockBasedTable* table_;
std::unordered_map<uint64_t, CachableEntry<Block>>* block_map_;
};
// Stores all the properties associated with a BlockBasedTable.
// These are immutable.
struct BlockBasedTable::Rep {
Rep(const ImmutableCFOptions& _ioptions, const EnvOptions& _env_options,
const BlockBasedTableOptions& _table_opt,
const InternalKeyComparator& _internal_comparator, bool skip_filters,
uint64_t _file_size, int _level, const bool _immortal_table)
: ioptions(_ioptions),
env_options(_env_options),
table_options(_table_opt),
filter_policy(skip_filters ? nullptr : _table_opt.filter_policy.get()),
internal_comparator(_internal_comparator),
filter_type(FilterType::kNoFilter),
index_type(BlockBasedTableOptions::IndexType::kBinarySearch),
hash_index_allow_collision(false),
whole_key_filtering(_table_opt.whole_key_filtering),
prefix_filtering(true),
global_seqno(kDisableGlobalSequenceNumber),
file_size(_file_size),
level(_level),
immortal_table(_immortal_table) {
}
~Rep() { status.PermitUncheckedError(); }
const ImmutableCFOptions& ioptions;
const EnvOptions& env_options;
const BlockBasedTableOptions table_options;
const FilterPolicy* const filter_policy;
const InternalKeyComparator& internal_comparator;
Status status;
std::unique_ptr<RandomAccessFileReader> file;
char cache_key_prefix[kMaxCacheKeyPrefixSize];
size_t cache_key_prefix_size = 0;
char persistent_cache_key_prefix[kMaxCacheKeyPrefixSize];
size_t persistent_cache_key_prefix_size = 0;
char compressed_cache_key_prefix[kMaxCacheKeyPrefixSize];
size_t compressed_cache_key_prefix_size = 0;
PersistentCacheOptions persistent_cache_options;
// Footer contains the fixed table information
Footer footer;
std::unique_ptr<IndexReader> index_reader;
std::unique_ptr<FilterBlockReader> filter;
std::unique_ptr<UncompressionDictReader> uncompression_dict_reader;
enum class FilterType {
kNoFilter,
kFullFilter,
kBlockFilter,
kPartitionedFilter,
};
FilterType filter_type;
BlockHandle filter_handle;
BlockHandle compression_dict_handle;
std::shared_ptr<const TableProperties> table_properties;
BlockBasedTableOptions::IndexType index_type;
bool hash_index_allow_collision;
bool whole_key_filtering;
bool prefix_filtering;
// TODO(kailiu) It is very ugly to use internal key in table, since table
// module should not be relying on db module. However to make things easier
// and compatible with existing code, we introduce a wrapper that allows
// block to extract prefix without knowing if a key is internal or not.
// null if no prefix_extractor is passed in when opening the table reader.
std::unique_ptr<SliceTransform> internal_prefix_transform;
std::shared_ptr<const SliceTransform> table_prefix_extractor;
std::shared_ptr<const FragmentedRangeTombstoneList> fragmented_range_dels;
// If global_seqno is used, all Keys in this file will have the same
// seqno with value `global_seqno`.
//
// A value of kDisableGlobalSequenceNumber means that this feature is disabled
// and every key have it's own seqno.
SequenceNumber global_seqno;
// Size of the table file on disk
uint64_t file_size;
// the level when the table is opened, could potentially change when trivial
// move is involved
int level;
// If false, blocks in this file are definitely all uncompressed. Knowing this
// before reading individual blocks enables certain optimizations.
bool blocks_maybe_compressed = true;
// If true, data blocks in this file are definitely ZSTD compressed. If false
// they might not be. When false we skip creating a ZSTD digested
// uncompression dictionary. Even if we get a false negative, things should
// still work, just not as quickly.
bool blocks_definitely_zstd_compressed = false;
// These describe how index is encoded.
bool index_has_first_key = false;
bool index_key_includes_seq = true;
bool index_value_is_full = true;
const bool immortal_table;
SequenceNumber get_global_seqno(BlockType block_type) const {
return (block_type == BlockType::kFilter ||
block_type == BlockType::kCompressionDictionary)
? kDisableGlobalSequenceNumber
: global_seqno;
}
uint64_t cf_id_for_tracing() const {
return table_properties
? table_properties->column_family_id
: ROCKSDB_NAMESPACE::TablePropertiesCollectorFactory::Context::
kUnknownColumnFamily;
}
Slice cf_name_for_tracing() const {
return table_properties ? table_properties->column_family_name
: BlockCacheTraceHelper::kUnknownColumnFamilyName;
}
uint32_t level_for_tracing() const { return level >= 0 ? level : UINT32_MAX; }
uint64_t sst_number_for_tracing() const {
return file ? TableFileNameToNumber(file->file_name()) : UINT64_MAX;
}
void CreateFilePrefetchBuffer(size_t readahead_size,
size_t max_readahead_size,
std::unique_ptr<FilePrefetchBuffer>* fpb,
bool implicit_auto_readahead) const {
fpb->reset(new FilePrefetchBuffer(
file.get(), readahead_size, max_readahead_size,
!ioptions.allow_mmap_reads /* enable */, false /* track_min_offset*/,
implicit_auto_readahead));
}
void CreateFilePrefetchBufferIfNotExists(
size_t readahead_size, size_t max_readahead_size,
std::unique_ptr<FilePrefetchBuffer>* fpb,
bool implicit_auto_readahead) const {
if (!(*fpb)) {
CreateFilePrefetchBuffer(readahead_size, max_readahead_size, fpb,
implicit_auto_readahead);
}
}
};
// This is an adapter class for `WritableFile` to be used for `std::ostream`.
// The adapter wraps a `WritableFile`, which can be passed to a `std::ostream`
// constructor for storing streaming data.
// Note:
// * This adapter doesn't provide any buffering, each write is forwarded to
// `WritableFile->Append()` directly.
// * For a failed write, the user needs to check the status by `ostream.good()`
class WritableFileStringStreamAdapter : public std::stringbuf {
public:
explicit WritableFileStringStreamAdapter(WritableFile* writable_file)
: file_(writable_file) {}
// Override overflow() to handle `sputc()`. There are cases that will not go
// through `xsputn()` e.g. `std::endl` or an unsigned long long is written by
// `os.put()` directly and will call `sputc()` By internal implementation:
// int_type __CLR_OR_THIS_CALL sputc(_Elem _Ch) { // put a character
// return 0 < _Pnavail() ? _Traits::to_int_type(*_Pninc() = _Ch) :
// overflow(_Traits::to_int_type(_Ch));
// }
// As we explicitly disabled buffering (_Pnavail() is always 0), every write,
// not captured by xsputn(), becomes an overflow here.
int overflow(int ch = EOF) override {
if (ch != EOF) {
Status s = file_->Append(Slice((char*)&ch, 1));
if (s.ok()) {
return ch;
}
}
return EOF;
}
std::streamsize xsputn(char const* p, std::streamsize n) override {
Status s = file_->Append(Slice(p, n));
if (!s.ok()) {
return 0;
}
return n;
}
private:
WritableFile* file_;
};
} // namespace ROCKSDB_NAMESPACE