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rocksdb/table/plain_table_reader.h

222 lines
8.2 KiB

// 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 <unordered_map>
#include <memory>
#include <vector>
#include <string>
#include <stdint.h>
#include "db/dbformat.h"
#include "rocksdb/env.h"
#include "rocksdb/iterator.h"
#include "rocksdb/slice_transform.h"
#include "rocksdb/table.h"
#include "rocksdb/table_properties.h"
#include "table/table_reader.h"
#include "table/plain_table_factory.h"
namespace rocksdb {
class Block;
class BlockHandle;
class Footer;
struct Options;
class RandomAccessFile;
struct ReadOptions;
class TableCache;
class TableReader;
class DynamicBloom;
class InternalKeyComparator;
using std::unique_ptr;
using std::unordered_map;
extern const uint32_t kPlainTableVariableLength;
// Based on following output file format shown in plain_table_factory.h
// When opening the output file, IndexedTableReader creates a hash table
// from key prefixes to offset of the output file. IndexedTable will decide
// whether it points to the data offset of the first key with the key prefix
// or the offset of it. If there are too many keys share this prefix, it will
// create a binary search-able index from the suffix to offset on disk.
//
// The implementation of IndexedTableReader requires output file is mmaped
class PlainTableReader: public TableReader {
public:
static Status Open(const Options& options, const EnvOptions& soptions,
const InternalKeyComparator& internal_comparator,
unique_ptr<RandomAccessFile>&& file, uint64_t file_size,
unique_ptr<TableReader>* table,
const int bloom_bits_per_key, double hash_table_ratio);
bool PrefixMayMatch(const Slice& internal_prefix);
Iterator* NewIterator(const ReadOptions&);
Status Get(const ReadOptions&, const Slice& key, void* arg,
bool (*result_handler)(void* arg, const ParsedInternalKey& k,
const Slice& v, bool),
void (*mark_key_may_exist)(void*) = nullptr);
uint64_t ApproximateOffsetOf(const Slice& key);
void SetupForCompaction();
std::shared_ptr<const TableProperties> GetTableProperties() const {
return table_properties_;
}
PlainTableReader(const EnvOptions& storage_options,
const InternalKeyComparator& internal_comparator,
uint64_t file_size, int bloom_num_bits,
double hash_table_ratio,
const TableProperties* table_properties);
~PlainTableReader();
private:
struct IndexRecord;
class IndexRecordList;
uint32_t* hash_table_ = nullptr;
int hash_table_size_ = 0;
char* sub_index_ = nullptr;
Options options_;
const EnvOptions& soptions_;
const InternalKeyComparator internal_comparator_;
Status status_;
unique_ptr<RandomAccessFile> file_;
Slice file_data_;
uint32_t version_;
uint32_t file_size_;
const double kHashTableRatio;
const int kBloomBitsPerKey;
DynamicBloom* bloom_ = nullptr;
std::shared_ptr<const TableProperties> table_properties_;
const uint32_t data_start_offset_ = 0;
const uint32_t data_end_offset_;
const size_t user_key_len_;
static const size_t kNumInternalBytes = 8;
static const uint32_t kSubIndexMask = 0x80000000;
static const size_t kOffsetLen = sizeof(uint32_t);
static const uint64_t kMaxFileSize = 1u << 31;
static const size_t kRecordsPerGroup = 256;
// To speed up the search for keys with same prefix, we'll add index key for
// every N keys, where the "N" is determined by
// kIndexIntervalForSamePrefixKeys
static const size_t kIndexIntervalForSamePrefixKeys = 16;
bool IsFixedLength() const {
return user_key_len_ != kPlainTableVariableLength;
}
size_t GetFixedInternalKeyLength() const {
return user_key_len_ + kNumInternalBytes;
}
friend class TableCache;
friend class PlainTableIterator;
// Internal helper function to generate an IndexRecordList object from all
// the rows, which contains index records as a list.
int PopulateIndexRecordList(IndexRecordList* record_list);
// Internal helper function to allocate memory for indexes and bloom filters
void AllocateIndexAndBloom(int num_prefixes);
// Internal helper function to bucket index record list to hash buckets.
// hash_to_offsets is sized of of hash_table_size_, each contains a linked
// list
// of offsets for the hash, in reversed order.
// bucket_count is sized of hash_table_size_. The value is how many index
// records are there in hash_to_offsets for the same bucket.
size_t BucketizeIndexesAndFillBloom(
IndexRecordList& record_list, int num_prefixes,
std::vector<IndexRecord*>* hash_to_offsets,
std::vector<uint32_t>* bucket_count);
// Internal helper class to fill the indexes and bloom filters to internal
// data structures. hash_to_offsets and bucket_count are bucketized indexes
// and counts generated by BucketizeIndexesAndFillBloom().
void FillIndexes(size_t sub_index_size_needed,
const std::vector<IndexRecord*>& hash_to_offsets,
const std::vector<uint32_t>& bucket_count);
// PopulateIndex() builds index of keys. It must be called before any query
// to the table.
//
// hash_table_ contains buckets size of hash_table_size_, each is a 32-bit
// integer. The lower 31 bits contain an offset value (explained below) and
// the first bit of the integer indicates type of the offset.
//
// +--------------+------------------------------------------------------+
// | Flag (1 bit) | Offset to binary search buffer or file (31 bits) +
// +--------------+------------------------------------------------------+
//
// Explanation for the "flag bit":
//
// 0 indicates that the bucket contains only one prefix (no conflict when
// hashing this prefix), whose first row starts from this offset of the
// file.
// 1 indicates that the bucket contains more than one prefixes, or there
// are too many rows for one prefix so we need a binary search for it. In
// this case, the offset indicates the offset of sub_index_ holding the
// binary search indexes of keys for those rows. Those binary search indexes
// are organized in this way:
//
// The first 4 bytes, indicate how many indexes (N) are stored after it. After
// it, there are N 32-bit integers, each points of an offset of the file,
// which
// points to starting of a row. Those offsets need to be guaranteed to be in
// ascending order so the keys they are pointing to are also in ascending
// order
// to make sure we can use them to do binary searches. Below is visual
// presentation of a bucket.
//
// <begin>
// number_of_records: varint32
// record 1 file offset: fixedint32
// record 2 file offset: fixedint32
// ....
// record N file offset: fixedint32
// <end>
Status PopulateIndex();
// Check bloom filter to see whether it might contain this prefix.
// The hash of the prefix is given, since it can be reused for index lookup
// too.
bool MayHavePrefix(uint32_t hash);
Status ReadKey(const char* row_ptr, ParsedInternalKey* key,
size_t& bytes_read);
// Read the key and value at offset to key and value.
// tmp_slice is a tmp slice.
// return next_offset as the offset for the next key.
Status Next(uint32_t offset, ParsedInternalKey* key, Slice* value,
uint32_t& next_offset);
// Get file offset for key target.
// return value prefix_matched is set to true if the offset is confirmed
// for a key with the same prefix as target.
Status GetOffset(const Slice& target, const Slice& prefix,
uint32_t prefix_hash, bool& prefix_matched,
uint32_t& ret_offset);
Slice GetPrefix(const Slice& target) {
assert(target.size() >= 8); // target is internal key
return options_.prefix_extractor->Transform(
Slice(target.data(), target.size() - 8));
}
Slice GetPrefix(const ParsedInternalKey& target);
// No copying allowed
explicit PlainTableReader(const TableReader&) = delete;
void operator=(const TableReader&) = delete;
};
} // namespace rocksdb