mirror of https://github.com/facebook/rocksdb.git
181 lines
7.3 KiB
C++
181 lines
7.3 KiB
C++
// Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
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// 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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#include <stdint.h>
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#include <memory>
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#include <string>
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#include "rocksdb/table.h"
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namespace ROCKSDB_NAMESPACE {
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struct EnvOptions;
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class Status;
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class RandomAccessFile;
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class WritableFile;
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class Table;
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class TableBuilder;
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// PlainTableFactory is the entrance function to the PlainTable format of
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// SST files. It returns instances PlainTableBuilder as the builder
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// class and PlainTableReader as the reader class, where the format is
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// actually implemented.
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//
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// The PlainTable is designed for memory-mapped file systems, e.g. tmpfs.
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// Data is not organized in blocks, which allows fast access. Because of
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// following downsides
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// 1. Data compression is not supported.
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// 2. Data is not checksumed.
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// it is not recommended to use this format on other type of file systems.
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//
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// PlainTable requires fixed length key, configured as a constructor
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// parameter of the factory class. Output file format:
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// +-------------+-----------------+
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// | version | user_key_length |
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// +------------++------------+-----------------+ <= key1 offset
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// | encoded key1 | value_size | |
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// +------------+-------------+-------------+ |
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// | value1 |
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// | |
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// +--------------------------+-------------+---+ <= key2 offset
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// | encoded key2 | value_size | |
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// +------------+-------------+-------------+ |
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// | value2 |
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// | |
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// | ...... |
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// +-----------------+--------------------------+
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//
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// When the key encoding type is kPlain. Key part is encoded as:
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// +------------+--------------------+
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// | [key_size] | internal key |
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// +------------+--------------------+
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// for the case of user_key_len = kPlainTableVariableLength case,
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// and simply:
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// +----------------------+
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// | internal key |
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// +----------------------+
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// for user_key_len != kPlainTableVariableLength case.
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//
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// If key encoding type is kPrefix. Keys are encoding in this format.
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// There are three ways to encode a key:
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// (1) Full Key
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// +---------------+---------------+-------------------+
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// | Full Key Flag | Full Key Size | Full Internal Key |
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// +---------------+---------------+-------------------+
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// which simply encodes a full key
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//
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// (2) A key shared the same prefix as the previous key, which is encoded as
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// format of (1).
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// +-------------+-------------+-------------+-------------+------------+
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// | Prefix Flag | Prefix Size | Suffix Flag | Suffix Size | Key Suffix |
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// +-------------+-------------+-------------+-------------+------------+
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// where key is the suffix part of the key, including the internal bytes.
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// the actual key will be constructed by concatenating prefix part of the
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// previous key, with the suffix part of the key here, with sizes given here.
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//
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// (3) A key shared the same prefix as the previous key, which is encoded as
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// the format of (2).
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// +-----------------+-----------------+------------------------+
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// | Key Suffix Flag | Key Suffix Size | Suffix of Internal Key |
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// +-----------------+-----------------+------------------------+
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// The key will be constructed by concatenating previous key's prefix (which is
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// also a prefix which the last key encoded in the format of (1)) and the
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// key given here.
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//
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// For example, we for following keys (prefix and suffix are separated by
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// spaces):
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// 0000 0001
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// 0000 00021
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// 0000 0002
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// 00011 00
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// 0002 0001
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// Will be encoded like this:
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// FK 8 00000001
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// PF 4 SF 5 00021
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// SF 4 0002
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// FK 7 0001100
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// FK 8 00020001
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// (where FK means full key flag, PF means prefix flag and SF means suffix flag)
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//
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// All those "key flag + key size" shown above are in this format:
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// The 8 bits of the first byte:
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// +----+----+----+----+----+----+----+----+
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// | Type | Size |
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// +----+----+----+----+----+----+----+----+
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// Type indicates: full key, prefix, or suffix.
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// The last 6 bits are for size. If the size bits are not all 1, it means the
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// size of the key. Otherwise, varint32 is read after this byte. This varint
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// value + 0x3F (the value of all 1) will be the key size.
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//
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// For example, full key with length 16 will be encoded as (binary):
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// 00 010000
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// (00 means full key)
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// and a prefix with 100 bytes will be encoded as:
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// 01 111111 00100101
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// (63) (37)
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// (01 means key suffix)
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//
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// All the internal keys above (including kPlain and kPrefix) are encoded in
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// this format:
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// There are two types:
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// (1) normal internal key format
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// +----------- ...... -------------+----+---+---+---+---+---+---+---+
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// | user key |type| sequence ID |
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// +----------- ..... --------------+----+---+---+---+---+---+---+---+
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// (2) Special case for keys whose sequence ID is 0 and is value type
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// +----------- ...... -------------+----+
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// | user key |0x80|
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// +----------- ..... --------------+----+
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// To save 7 bytes for the special case where sequence ID = 0.
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//
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//
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class PlainTableFactory : public TableFactory {
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public:
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~PlainTableFactory() {}
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// user_key_len is the length of the user key. If it is set to be
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// kPlainTableVariableLength, then it means variable length. Otherwise, all
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// the keys need to have the fix length of this value. bloom_bits_per_key is
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// number of bits used for bloom filer per key. hash_table_ratio is
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// the desired utilization of the hash table used for prefix hashing.
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// hash_table_ratio = number of prefixes / #buckets in the hash table
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// hash_table_ratio = 0 means skip hash table but only replying on binary
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// search.
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// index_sparseness determines index interval for keys
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// inside the same prefix. It will be the maximum number of linear search
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// required after hash and binary search.
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// index_sparseness = 0 means index for every key.
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// huge_page_tlb_size determines whether to allocate hash indexes from huge
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// page TLB and the page size if allocating from there. See comments of
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// Arena::AllocateAligned() for details.
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explicit PlainTableFactory(
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const PlainTableOptions& _table_options = PlainTableOptions());
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// Method to allow CheckedCast to work for this class
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static const char* kClassName() { return kPlainTableName(); }
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const char* Name() const override { return kPlainTableName(); }
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using TableFactory::NewTableReader;
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Status NewTableReader(const ReadOptions& ro,
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const TableReaderOptions& table_reader_options,
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std::unique_ptr<RandomAccessFileReader>&& file,
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uint64_t file_size, std::unique_ptr<TableReader>* table,
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bool prefetch_index_and_filter_in_cache) const override;
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TableBuilder* NewTableBuilder(
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const TableBuilderOptions& table_builder_options,
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WritableFileWriter* file) const override;
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std::string GetPrintableOptions() const override;
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static const char kValueTypeSeqId0 = char(~0);
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private:
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PlainTableOptions table_options_;
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};
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} // namespace ROCKSDB_NAMESPACE
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