fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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175 lines
7.7 KiB
175 lines
7.7 KiB
// 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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//
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// Currently we support two types of tables: plain table and block-based table.
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// 1. Block-based table: this is the default table type that we inherited from
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// LevelDB, which was designed for storing data in hard disk or flash
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// device.
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// 2. Plain table: it is one of RocksDB's SST file format optimized
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// for low query latency on pure-memory or really low-latency media.
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//
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// A tutorial of rocksdb table formats is available here:
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// https://github.com/facebook/rocksdb/wiki/A-Tutorial-of-RocksDB-SST-formats
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//
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// Example code is also available
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// https://github.com/facebook/rocksdb/wiki/A-Tutorial-of-RocksDB-SST-formats#wiki-examples
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#pragma once
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#include <memory>
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#include <string>
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#include <unordered_map>
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#include "rocksdb/env.h"
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#include "rocksdb/iterator.h"
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#include "rocksdb/options.h"
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#include "rocksdb/status.h"
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namespace rocksdb {
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// -- Block-based Table
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class FlushBlockPolicyFactory;
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class RandomAccessFile;
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class TableBuilder;
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class TableReader;
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class WritableFile;
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struct EnvOptions;
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struct Options;
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using std::unique_ptr;
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// For advanced user only
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struct BlockBasedTableOptions {
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// @flush_block_policy_factory creates the instances of flush block policy.
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// which provides a configurable way to determine when to flush a block in
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// the block based tables. If not set, table builder will use the default
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// block flush policy, which cut blocks by block size (please refer to
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// `FlushBlockBySizePolicy`).
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std::shared_ptr<FlushBlockPolicyFactory> flush_block_policy_factory;
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// TODO(kailiu) Temporarily disable this feature by making the default value
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// to be false.
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//
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// Indicating if we'd put index/filter blocks to the block cache.
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// If not specified, each "table reader" object will pre-load index/filter
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// block during table initialization.
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bool cache_index_and_filter_blocks = false;
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// The index type that will be used for this table.
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enum IndexType : char {
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// A space efficient index block that is optimized for
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// binary-search-based index.
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kBinarySearch,
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};
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IndexType index_type = kBinarySearch;
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};
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// Table Properties that are specific to block-based table properties.
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struct BlockBasedTablePropertyNames {
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// value of this propertis is a fixed int32 number.
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static const std::string kIndexType;
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};
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// Create default block based table factory.
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extern TableFactory* NewBlockBasedTableFactory(
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const BlockBasedTableOptions& table_options = BlockBasedTableOptions());
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// -- Plain Table with prefix-only seek
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// For this factory, you need to set Options.prefix_extrator properly to make it
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// work. Look-up will starts with prefix hash lookup for key prefix. Inside the
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// hash bucket found, a binary search is executed for hash conflicts. Finally,
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// a linear search is used.
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// @user_key_len: plain table has optimization for fix-sized keys, which can be
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// specified via user_key_len. Alternatively, you can pass
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// `kPlainTableVariableLength` if your keys have variable
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// lengths.
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// @bloom_bits_per_key: the number of bits used for bloom filer per prefix. You
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// may disable it by passing a zero.
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// @hash_table_ratio: the desired utilization of the hash table used for prefix
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// hashing. hash_table_ratio = number of prefixes / #buckets
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// in the hash table
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// @index_sparseness: inside each prefix, need to build one index record for how
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// many keys for binary search inside each hash bucket.
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const uint32_t kPlainTableVariableLength = 0;
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extern TableFactory* NewPlainTableFactory(uint32_t user_key_len =
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kPlainTableVariableLength,
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int bloom_bits_per_prefix = 10,
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double hash_table_ratio = 0.75,
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size_t index_sparseness = 16);
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// -- Plain Table
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// This factory of plain table ignores Options.prefix_extractor and assumes no
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// hashable prefix available to the key structure. Lookup will be based on
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// binary search index only. Total order seek() can be issued.
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// @user_key_len: plain table has optimization for fix-sized keys, which can be
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// specified via user_key_len. Alternatively, you can pass
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// `kPlainTableVariableLength` if your keys have variable
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// lengths.
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// @bloom_bits_per_key: the number of bits used for bloom filer per key. You may
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// disable it by passing a zero.
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// @index_sparseness: need to build one index record for how many keys for
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// binary search.
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extern TableFactory* NewTotalOrderPlainTableFactory(
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uint32_t user_key_len = kPlainTableVariableLength,
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int bloom_bits_per_key = 0, size_t index_sparseness = 16);
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// A base class for table factories.
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class TableFactory {
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public:
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virtual ~TableFactory() {}
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// The type of the table.
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//
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// The client of this package should switch to a new name whenever
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// the table format implementation changes.
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//
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// Names starting with "rocksdb." are reserved and should not be used
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// by any clients of this package.
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virtual const char* Name() const = 0;
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// Returns a Table object table that can fetch data from file specified
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// in parameter file. It's the caller's responsibility to make sure
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// file is in the correct format.
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//
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// NewTableReader() is called in two places:
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// (1) TableCache::FindTable() calls the function when table cache miss
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// and cache the table object returned.
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// (1) SstFileReader (for SST Dump) opens the table and dump the table
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// contents using the interator of the table.
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// options and soptions are options. options is the general options.
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// Multiple configured can be accessed from there, including and not
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// limited to block cache and key comparators.
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// file is a file handler to handle the file for the table
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// file_size is the physical file size of the file
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// table_reader is the output table reader
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virtual Status NewTableReader(
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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_reader) const = 0;
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// Return a table builder to write to a file for this table type.
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//
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// It is called in several places:
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// (1) When flushing memtable to a level-0 output file, it creates a table
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// builder (In DBImpl::WriteLevel0Table(), by calling BuildTable())
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// (2) During compaction, it gets the builder for writing compaction output
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// files in DBImpl::OpenCompactionOutputFile().
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// (3) When recovering from transaction logs, it creates a table builder to
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// write to a level-0 output file (In DBImpl::WriteLevel0TableForRecovery,
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// by calling BuildTable())
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// (4) When running Repairer, it creates a table builder to convert logs to
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// SST files (In Repairer::ConvertLogToTable() by calling BuildTable())
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//
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// options is the general options. Multiple configured can be acceseed from
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// there, including and not limited to compression options.
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// file is a handle of a writable file. It is the caller's responsibility to
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// keep the file open and close the file after closing the table builder.
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// compression_type is the compression type to use in this table.
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virtual TableBuilder* NewTableBuilder(
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const Options& options, const InternalKeyComparator& internal_comparator,
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WritableFile* file, CompressionType compression_type) const = 0;
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};
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} // namespace rocksdb
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