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rocksdb/table/block_based_table_reader.h

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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same 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 <memory>
#include <stdint.h>
#include "rocksdb/cache.h"
#include "rocksdb/env.h"
#include "rocksdb/iterator.h"
#include "rocksdb/statistics.h"
#include "table/table_reader.h"
#include "util/coding.h"
namespace rocksdb {
class Block;
class BlockHandle;
class Footer;
struct Options;
class RandomAccessFile;
struct ReadOptions;
class TableCache;
class TableReader;
class FilterBlockReader;
struct BlockBasedTableOptions;
using std::unique_ptr;
// A Table is a sorted map from strings to strings. Tables are
// immutable and persistent. A Table may be safely accessed from
// multiple threads without external synchronization.
class BlockBasedTable : public TableReader {
public:
static const std::string kFilterBlockPrefix;
// 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.
//
// *file must remain live while this Table is in use.
static Status Open(const Options& db_options, const EnvOptions& env_options,
const BlockBasedTableOptions& table_options,
const InternalKeyComparator& internal_key_comparator,
unique_ptr<RandomAccessFile>&& file, uint64_t file_size,
unique_ptr<TableReader>* table_reader);
bool PrefixMayMatch(const Slice& internal_prefix) override;
// 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).
Iterator* NewIterator(const ReadOptions&) override;
Status Get(const ReadOptions& readOptions, const Slice& key,
void* handle_context,
bool (*result_handler)(void* handle_context,
const ParsedInternalKey& k, const Slice& v,
bool didIO),
void (*mark_key_may_exist_handler)(void* handle_context) =
nullptr) 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) override;
// Returns true if the block for the specified key is in cache.
// REQUIRES: key is in this table.
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;
const TableProperties& GetTableProperties() override;
~BlockBasedTable();
private:
template <class TValue>
struct CachableEntry;
struct Rep;
Rep* rep_;
bool compaction_optimized_;
static Iterator* BlockReader(void*, const ReadOptions&,
const EnvOptions& soptions,
const InternalKeyComparator& icomparator,
const Slice&, bool for_compaction);
static Iterator* BlockReader(void*, const ReadOptions&, const Slice&,
bool* didIO, bool for_compaction = false);
// if `no_io == true`, we will not try to read filter from sst file
// if it is not cached yet.
CachableEntry<FilterBlockReader> GetFilter(bool no_io = false) const;
Iterator* IndexBlockReader(const ReadOptions& options) const;
// Read the block, either from sst file or from cache. This method will try
// to read from cache only when block_cache is set or ReadOption doesn't
// explicitly prohibit storage IO.
//
// If the block is read from cache, the statistics for cache miss/hit of the
// the given type of block will be updated. User can specify
// `block_cache_miss_ticker` and `block_cache_hit_ticker` for the statistics
// update.
//
// On success, the `result` parameter will be populated, which contains a
// pointer to the block and its cache handle, which will be nullptr if it's
// not read from the cache.
static Status GetBlock(const BlockBasedTable* table,
const BlockHandle& handle,
const ReadOptions& options,
bool for_compaction,
Tickers block_cache_miss_ticker,
Tickers block_cache_hit_ticker,
bool* didIO,
CachableEntry<Block>* result);
// 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;
void ReadMeta(const Footer& footer);
void ReadFilter(const Slice& filter_handle_value);
// Read the meta block from sst.
static Status ReadMetaBlock(
Rep* rep,
std::unique_ptr<Block>* meta_block,
std::unique_ptr<Iterator>* iter);
// Create the filter from the filter block.
static FilterBlockReader* ReadFilter(
const Slice& filter_handle_value,
Rep* rep,
size_t* filter_size = nullptr);
static void SetupCacheKeyPrefix(Rep* rep);
explicit BlockBasedTable(Rep* rep) :
compaction_optimized_(false) {
rep_ = rep;
}
// Generate a cache key prefix from the file
static void GenerateCachePrefix(Cache* cc,
RandomAccessFile* file, char* buffer, size_t* size);
static void GenerateCachePrefix(Cache* cc,
WritableFile* file, char* buffer, size_t* size);
// 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;
// No copying allowed
explicit BlockBasedTable(const TableReader&) = delete;
void operator=(const TableReader&) = delete;
};
} // namespace rocksdb