mirror of
https://github.com/facebook/rocksdb.git
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266 lines
9.9 KiB
C++
266 lines
9.9 KiB
C++
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#pragma once
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#ifndef ROCKSDB_LITE
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#include <unordered_map>
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#include <memory>
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#include <vector>
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#include <string>
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#include <stdint.h>
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#include "db/dbformat.h"
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#include "rocksdb/env.h"
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#include "rocksdb/iterator.h"
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#include "rocksdb/slice_transform.h"
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#include "rocksdb/table.h"
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#include "rocksdb/table_properties.h"
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#include "table/table_reader.h"
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#include "table/plain_table_factory.h"
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#include "util/arena.h"
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namespace rocksdb {
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class Block;
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class BlockHandle;
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class Footer;
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struct Options;
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class RandomAccessFile;
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struct ReadOptions;
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class TableCache;
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class TableReader;
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class DynamicBloom;
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class InternalKeyComparator;
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using std::unique_ptr;
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using std::unordered_map;
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extern const uint32_t kPlainTableVariableLength;
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// Based on following output file format shown in plain_table_factory.h
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// When opening the output file, IndexedTableReader creates a hash table
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// from key prefixes to offset of the output file. IndexedTable will decide
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// whether it points to the data offset of the first key with the key prefix
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// or the offset of it. If there are too many keys share this prefix, it will
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// create a binary search-able index from the suffix to offset on disk.
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//
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// The implementation of IndexedTableReader requires output file is mmaped
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class PlainTableReader: public TableReader {
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public:
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static Status Open(const Options& options, const EnvOptions& soptions,
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const InternalKeyComparator& internal_comparator,
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unique_ptr<RandomAccessFile>&& file, uint64_t file_size,
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unique_ptr<TableReader>* table,
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const int bloom_bits_per_key, double hash_table_ratio,
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size_t index_sparseness, size_t huge_page_tlb_size);
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Iterator* NewIterator(const ReadOptions&);
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Status Get(const ReadOptions&, const Slice& key, void* arg,
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bool (*result_handler)(void* arg, const ParsedInternalKey& k,
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const Slice& v, bool),
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void (*mark_key_may_exist)(void*) = nullptr);
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uint64_t ApproximateOffsetOf(const Slice& key);
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void SetupForCompaction();
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std::shared_ptr<const TableProperties> GetTableProperties() const {
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return table_properties_;
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}
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PlainTableReader(const Options& options, unique_ptr<RandomAccessFile>&& file,
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const EnvOptions& storage_options,
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const InternalKeyComparator& internal_comparator,
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uint64_t file_size, int bloom_num_bits,
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double hash_table_ratio, size_t index_sparseness,
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const TableProperties* table_properties,
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size_t huge_page_tlb_size);
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virtual ~PlainTableReader();
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protected:
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// Check bloom filter to see whether it might contain this prefix.
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// The hash of the prefix is given, since it can be reused for index lookup
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// too.
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virtual bool MatchBloom(uint32_t hash) const;
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// PopulateIndex() builds index of keys. It must be called before any query
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// to the table.
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//
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// props: the table properties object that need to be stored. Ownership of
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// the object will be passed.
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//
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// index_ contains buckets size of index_size_, each is a
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// 32-bit integer. The lower 31 bits contain an offset value (explained below)
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// and the first bit of the integer indicates type of the offset.
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//
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// +--------------+------------------------------------------------------+
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// | Flag (1 bit) | Offset to binary search buffer or file (31 bits) +
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// +--------------+------------------------------------------------------+
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//
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// Explanation for the "flag bit":
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//
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// 0 indicates that the bucket contains only one prefix (no conflict when
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// hashing this prefix), whose first row starts from this offset of the
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// file.
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// 1 indicates that the bucket contains more than one prefixes, or there
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// are too many rows for one prefix so we need a binary search for it. In
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// this case, the offset indicates the offset of sub_index_ holding the
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// binary search indexes of keys for those rows. Those binary search indexes
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// are organized in this way:
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//
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// The first 4 bytes, indicate how many indexes (N) are stored after it. After
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// it, there are N 32-bit integers, each points of an offset of the file,
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// which
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// points to starting of a row. Those offsets need to be guaranteed to be in
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// ascending order so the keys they are pointing to are also in ascending
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// order
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// to make sure we can use them to do binary searches. Below is visual
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// presentation of a bucket.
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//
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// <begin>
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// number_of_records: varint32
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// record 1 file offset: fixedint32
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// record 2 file offset: fixedint32
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// ....
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// record N file offset: fixedint32
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// <end>
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Status PopulateIndex(TableProperties* props);
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private:
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struct IndexRecord;
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class IndexRecordList;
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// Plain table maintains an index and a sub index.
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// index is implemented by a hash table.
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// subindex is a big of memory array.
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// For more details about the in-memory index, please refer to:
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// https://github.com/facebook/rocksdb/wiki/PlainTable-Format
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// #wiki-in-memory-index-format
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uint32_t* index_;
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int index_size_ = 0;
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char* sub_index_;
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Options options_;
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const EnvOptions& soptions_;
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unique_ptr<RandomAccessFile> file_;
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const InternalKeyComparator internal_comparator_;
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// represents plain table's current status.
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Status status_;
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Slice file_data_;
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uint32_t file_size_;
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const double kHashTableRatio;
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const int kBloomBitsPerKey;
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// To speed up the search for keys with same prefix, we'll add index key for
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// every N keys, where the "N" is determined by
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// kIndexIntervalForSamePrefixKeys
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const size_t kIndexIntervalForSamePrefixKeys = 16;
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// Bloom filter is used to rule out non-existent key
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unique_ptr<DynamicBloom> bloom_;
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Arena arena_;
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std::shared_ptr<const TableProperties> table_properties_;
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// data_start_offset_ and data_end_offset_ defines the range of the
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// sst file that stores data.
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const uint32_t data_start_offset_ = 0;
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const uint32_t data_end_offset_;
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const size_t user_key_len_;
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const size_t huge_page_tlb_size_;
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static const size_t kNumInternalBytes = 8;
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static const uint32_t kSubIndexMask = 0x80000000;
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static const size_t kOffsetLen = sizeof(uint32_t);
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static const uint64_t kMaxFileSize = 1u << 31;
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static const size_t kRecordsPerGroup = 256;
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bool IsFixedLength() const {
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return user_key_len_ != kPlainTableVariableLength;
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}
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size_t GetFixedInternalKeyLength() const {
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return user_key_len_ + kNumInternalBytes;
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}
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friend class TableCache;
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friend class PlainTableIterator;
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// Internal helper function to generate an IndexRecordList object from all
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// the rows, which contains index records as a list.
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// If bloom_ is not null, all the keys' full-key hash will be added to the
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// bloom filter.
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Status PopulateIndexRecordList(IndexRecordList* record_list,
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int* num_prefixes) const;
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// Internal helper function to allocate memory for indexes and bloom filters
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void AllocateIndexAndBloom(int num_prefixes);
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// Internal helper function to bucket index record list to hash buckets.
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// bucket_header is a vector of size hash_table_size_, with each entry
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// containing a linklist of IndexRecord hashed to the same bucket, in reverse
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// order.
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// of offsets for the hash, in reversed order.
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// entries_per_bucket is sized of index_size_. The value is how many index
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// records are there in bucket_headers for the same bucket.
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size_t BucketizeIndexesAndFillBloom(
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IndexRecordList* record_list, std::vector<IndexRecord*>* bucket_headers,
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std::vector<uint32_t>* entries_per_bucket);
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// Internal helper class to fill the indexes and bloom filters to internal
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// data structures. bucket_headers and entries_per_bucket are bucketized
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// indexes and counts generated by BucketizeIndexesAndFillBloom().
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void FillIndexes(const size_t kSubIndexSize,
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const std::vector<IndexRecord*>& bucket_headers,
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const std::vector<uint32_t>& entries_per_bucket);
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// Read a plain table key from the position `start`. The read content
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// will be written to `key` and the size of read bytes will be populated
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// in `bytes_read`.
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Status ReadKey(const char* row_ptr, ParsedInternalKey* key,
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size_t* bytes_read) const;
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// Read the key and value at `offset` to parameters `key` and `value`.
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// On success, `offset` will be updated as the offset for the next key.
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Status Next(uint32_t* offset, ParsedInternalKey* key, Slice* value) const;
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// Get file offset for key target.
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// return value prefix_matched is set to true if the offset is confirmed
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// for a key with the same prefix as target.
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Status GetOffset(const Slice& target, const Slice& prefix,
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uint32_t prefix_hash, bool& prefix_matched,
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uint32_t* offset) const;
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Slice GetUserKey(const Slice& key) const {
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return Slice(key.data(), key.size() - 8);
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}
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Slice GetPrefix(const Slice& target) const {
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assert(target.size() >= 8); // target is internal key
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return GetPrefixFromUserKey(GetUserKey(target));
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}
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inline Slice GetPrefix(const ParsedInternalKey& target) const;
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Slice GetPrefixFromUserKey(const Slice& user_key) const {
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if (!IsTotalOrderMode()) {
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return options_.prefix_extractor->Transform(user_key);
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} else {
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// Use empty slice as prefix if prefix_extractor is not set. In that case,
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// it falls back to pure binary search and total iterator seek is
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// supported.
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return Slice();
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}
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}
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bool IsTotalOrderMode() const {
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return (options_.prefix_extractor.get() == nullptr);
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}
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// No copying allowed
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explicit PlainTableReader(const TableReader&) = delete;
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void operator=(const TableReader&) = delete;
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};
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} // namespace rocksdb
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#endif // ROCKSDB_LITE
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