Glossary

asynchronous

Not waiting for something to complete (e.g., sending data over the network to another node), and not making any assumptions about how long it is going to take. See “Synchronous Versus Asynchronous Replication” , “Synchronous Versus Asynchronous Networks” , and “System Model and Reality” .

不等待某个操作完成（例如，向另一个节点发送数据），也不做任何关于操作所需时间的假设。请参考“同步与异步复制”、“同步与异步网络”和“系统模型与现实”。

atomic

1. In the context of concurrent operations: describing an operation that appears to take effect at a single point in time, so another concurrent process can never encounter the operation in a “half-finished” state. See also isolation .

   描述一个操作在同时发生时，出现在单个时间点，因此另一个并发进程永远不会遇到该操作处于“半完成”的状态。请参考隔离。

2. In the context of transactions: grouping together a set of writes that must either all be committed or all be rolled back, even if faults occur. See “Atomicity” and “Atomic Commit and Two-Phase Commit (2PC)” .

   在交易的背景下：将一组写入操作分组，无论发生何种故障，其必须全部提交或全部回滚。请参见“原子性”和“原子提交和两阶段提交(2PC)”。

backpressure

Forcing the sender of some data to slow down because the recipient cannot keep up with it. Also known as flow control . See “Messaging Systems” .

强制数据发送方减缓速度，因为接收方无法跟上。也称为流量控制。参见“消息系统”。

batch process

A computation that takes some fixed (and usually large) set of data as input and produces some other data as output, without modifying the input. See Chapter 10 .

一种计算，它以一些固定（通常很大）的数据集作为输入并产生一些其他数据作为输出，而不修改输入。请参见第十章。

bounded

Having some known upper limit or size. Used for example in the context of network delay (see “Timeouts and Unbounded Delays” ) and datasets (see the introduction to Chapter 11 ).

具有某些已知上限或大小。例如，在网络延迟（参见“超时和无界延迟”）和数据集（参见第11章介绍）的上下文中使用。

Byzantine fault

A node that behaves incorrectly in some arbitrary way, for example by sending contradictory or malicious messages to other nodes. See “Byzantine Faults” .

一个节点以某种任意的方式行为不当，例如向其他节点发送矛盾或恶意信息。请参见“拜占庭故障”。

cache

A component that remembers recently used data in order to speed up future reads of the same data. It is generally not complete: thus, if some data is missing from the cache, it has to be fetched from some underlying, slower data storage system that has a complete copy of the data.

一个记忆最近使用的数据以加速未来读取同样数据的组件。通常并不完整：如果缓存中遗漏了某些数据，则必须从底层、较慢的数据存储系统中获取完整的数据拷贝。

CAP theorem

A widely misunderstood theoretical result that is not useful in practice. See “The CAP theorem” .

一个在实践中没有用处且被广泛误解的理论结果。请查看“CAP定理”。

causality

The dependency between events that arises when one thing “happens before” another thing in a system. For example, a later event that is in response to an earlier event, or builds upon an earlier event, or should be understood in the light of an earlier event. See “The “happens-before” relationship and concurrency” and “Ordering and Causality” .

当一个事件“在某个系统中发生之前”，另一个事件发生时它们之间就出现了依赖关系。例如，后续事件是对先前事件的响应，是建立在先前事件之上，或者应该在先前事件的基础上加以理解。请参阅“The “happens-before” relationship and concurrency”和“Ordering and Causality”。

consensus

A fundamental problem in distributed computing, concerning getting several nodes to agree on something (for example, which node should be the leader for a database cluster). The problem is much harder than it seems at first glance. See “Fault-Tolerant Consensus” .

分散式計算中的根本問題，涉及使多個節點就某事達成一致（例如，應該是哪個節點成為數據庫集群的首領）。這個問題比看上去困難得多。請參閱“容錯共識”。

data warehouse

A database in which data from several different OLTP systems has been combined and prepared to be used for analytics purposes. See “Data Warehousing” .

将来自多个不同OLTP系统的数据组合并准备好用于分析目的的数据库。 参见“数据仓库”。

declarative

Describing the properties that something should have, but not the exact steps for how to achieve it. In the context of queries, a query optimizer takes a declarative query and decides how it should best be executed. See “Query Languages for Data” .

描述某物应该具有的特性，但不是如何实现它的确切步骤。在查询的上下文中，查询优化器会接收一个声明性的查询并决定如何最好地执行它。请参见“数据查询语言”。

denormalize

To introduce some amount of redundancy or duplication in a normalized dataset, typically in the form of a cache or index , in order to speed up reads. A denormalized value is a kind of precomputed query result, similar to a materialized view. See “Single-Object and Multi-Object Operations” and “Deriving several views from the same event log” .

在规范化数据集中引入一定程度的冗余或重复，通常以缓存或索引的形式来加速读取。非规范化值是一种预先计算的查询结果，类似于材料化视图。请参阅“单对象和多对象操作”和“从相同的事件日志派生多个视图”。

derived data

A dataset that is created from some other data through a repeatable process, which you could run again if necessary. Usually, derived data is needed to speed up a particular kind of read access to the data. Indexes, caches, and materialized views are examples of derived data. See the introduction to Part III .

衍生数据集是通过可重复的过程从其他数据中创建的，如果需要，您可以再次运行该过程。通常，衍生数据用于加快对数据的特定读取访问速度。索引、缓存和物化视图是衍生数据的示例。请参见第III部分的介绍。

deterministic

Describing a function that always produces the same output if you give it the same input. This means it cannot depend on random numbers, the time of day, network communication, or other unpredictable things.

描述一个函数，如果你给它相同的输入，它总是会产生相同的输出。这意味着它不能依赖于随机数、时间、网络通信或其他不可预测的事物。

distributed

Running on several nodes connected by a network. Characterized by partial failures : some part of the system may be broken while other parts are still working, and it is often impossible for the software to know what exactly is broken. See “Faults and Partial Failures” .

运行在由网络连接的多个节点上。特点是部分故障：系统的一些部分可能出现故障，而其他部分仍在工作，软件通常无法知道哪个部分出现故障。请参见“故障和部分故障”。

durable

Storing data in a way such that you believe it will not be lost, even if various faults occur. See “Durability” .

以一种方式存储数据，即使发生各种故障，您也认为数据不会丢失。参见“耐久性”。

ETL

Extract–Transform–Load. The process of extracting data from a source database, transforming it into a form that is more suitable for analytic queries, and loading it into a data warehouse or batch processing system. See “Data Warehousing” .

抽取-转换-加载。从源数据库中提取数据，将其转换为更适合进行分析查询的形式，并将其加载到数据仓库或批处理系统中的过程。参见“数据仓库”。

failover

In systems that have a single leader, failover is the process of moving the leadership role from one node to another. See “Handling Node Outages” .

在只有一个领导者的系统中，故障转移是将领导角色从一个节点移动到另一个节点的过程。请参见“处理节点故障”。

fault-tolerant

Able to recover automatically if something goes wrong (e.g., if a machine crashes or a network link fails). See “Reliability” .

自动恢复功能可在出现问题时（例如机器崩溃或网络链路故障）进行恢复。请参见“可靠性”。

flow control

See backpressure .

看背压。

follower

A replica that does not directly accept any writes from clients, but only processes data changes that it receives from a leader. Also known as a secondary , slave , read replica , or hot standby . See “Leaders and Followers” .

一种复制品，不直接接受客户端的任何写入操作，而是仅处理从领导者接收到的数据更改。也称为次要、从属、只读复制品或热备份。参见“领导者和跟随者”。

full-text search

Searching text by arbitrary keywords, often with additional features such as matching similarly spelled words or synonyms. A full-text index is a kind of secondary index that supports such queries. See “Full-text search and fuzzy indexes” .

通过任意关键字搜索文本，通常具有匹配拼写类似单词或同义词等其他功能。全文索引是一种支持此类查询的次要索引。参见“全文搜索和模糊索引”。

graph

A data structure consisting of vertices (things that you can refer to, also known as nodes or entities ) and edges (connections from one vertex to another, also known as relationships or arcs ). See “Graph-Like Data Models” .

一个由顶点（也称为节点或实体，可以引用的事物）和边缘（从一个顶点到另一个顶点的连接，也称为关系或弧）组成的数据结构。参见“类似图形的数据模型”。

hash

A function that turns an input into a random-looking number. The same input always returns the same number as output. Two different inputs are very likely to have two different numbers as output, although it is possible that two different inputs produce the same output (this is called a collision ). See “Partitioning by Hash of Key” .

一个将输入转换为随机外表数字的函数。相同的输入始终会返回相同的输出数字。两个不同的输入非常可能会产生不同的输出数字，虽然有可能两个不同的输入会产生相同的输出数字（这被称为冲突）。参见“按键哈希分区”。

idempotent

Describing an operation that can be safely retried; if it is executed more than once, it has the same effect as if it was only executed once. See “Idempotence” .

描述一个可以安全重试的操作；如果它被执行多次，它的效果与它只被执行一次相同。请参见“幂等性”。

index

A data structure that lets you efficiently search for all records that have a particular value in a particular field. See “Data Structures That Power Your Database” .

一种数据结构，可让您有效地搜索特定字段中具有特定值的所有记录。请参见“驱动您的数据库的数据结构”。

isolation

In the context of transactions, describing the degree to which concurrently executing transactions can interfere with each other. Serializable isolation provides the strongest guarantees, but weaker isolation levels are also used. See “Isolation” .

在交易的背景下，描述同时执行的交易之间会产生干扰的程度。串行化隔离提供最强的保证，但使用较弱的隔离级别也很常见。参见“隔离”。

join

To bring together records that have something in common. Most commonly used in the case where one record has a reference to another (a foreign key, a document reference, an edge in a graph) and a query needs to get the record that the reference points to. See “Many-to-One and Many-to-Many Relationships” and “Reduce-Side Joins and Grouping” .

将具有共同点的记录汇集在一起。通常用于一个记录引用另一个记录的情况（外键、文档引用、图中的边），并且查询需要获取引用所指向的记录。参见“一对多和多对多关系”和“Reduce-Side连接和分组”。

leader

When data or a service is replicated across several nodes, the leader is the designated replica that is allowed to make changes. A leader may be elected through some protocol, or manually chosen by an administrator. Also known as the primary or master . See “Leaders and Followers” .

当数据或服务被复制到多个节点时，领导者是被指定允许进行更改的副本。领导者可以通过某种协议选举，或由管理员手动选择。也称为主要或主控。请参见“领导者和跟随者”。

linearizable

Behaving as if there was only a single copy of data in the system, which is updated by atomic operations. See “Linearizability” .

表现得好像系统中只有单个数据副本，而该副本通过原子操作进行更新。请参见“线性化”。

locality

A performance optimization: putting several pieces of data in the same place if they are frequently needed at the same time. See “Data locality for queries” .

一个性能优化：如果一些数据在同一时间频繁地需要，将这些数据放在同一个位置。请参阅“查询的数据局部性”。

lock

A mechanism to ensure that only one thread, node, or transaction can access something, and anyone else who wants to access the same thing must wait until the lock is released. See “Two-Phase Locking (2PL)” and “The leader and the lock” .

确保只有一个线程、节点或事务可以访问某物，并且任何想要访问相同物品的人必须等待锁被释放的机制。参见“两阶段锁定（2PL）”和“领导者和锁”。

log

An append-only file for storing data. A write-ahead log is used to make a storage engine resilient against crashes (see “Making B-trees reliable” ), a log-structured storage engine uses logs as its primary storage format (see “SSTables and LSM-Trees” ), a replication log is used to copy writes from a leader to followers (see “Leaders and Followers” ), and an event log can represent a data stream (see “Partitioned Logs” ).

一个仅能附加的文件用于存储数据。采用写前日志来使存储引擎能够抵御崩溃（见“使B树可靠”），采用日志结构的存储引擎将日志用作其主要存储格式（见“SSTables和LSM-Trees”），复制日志用于将写操作从领导者复制到跟随者（见“领导者和跟随者”），事件日志可以表示数据流（见“分区日志”）。

materialize

To perform a computation eagerly and write out its result, as opposed to calculating it on demand when requested. See “Aggregation: Data Cubes and Materialized Views” and “Materialization of Intermediate State” .

急切地执行一项计算并输出结果，而不是在需要时计算。请参见“聚合：数据立方体和材料化视图”和“中间状态的材料化”。

node

An instance of some software running on a computer, which communicates with other nodes via a network in order to accomplish some task.

某台计算机上运行的软件实例，通过网络与其他节点通信，以完成某项任务。

normalized

Structured in such a way that there is no redundancy or duplication. In a normalized database, when some piece of data changes, you only need to change it in one place, not many copies in many different places. See “Many-to-One and Many-to-Many Relationships” .

规范化的数据库结构设计避免了冗余和重复的存在。当某个数据发生变化时，你只需要在一个地方修改，而不是在许多不同的地方修改。请参见“一对多和多对多关系”。

OLAP

Online analytic processing. Access pattern characterized by aggregating (e.g., count, sum, average) over a large number of records. See “Transaction Processing or Analytics?” .

在线分析处理。访问模式通过对大量记录进行聚合（如计数，求和，平均值）来表征。参见“事务处理还是分析？”。

OLTP

Online transaction processing. Access pattern characterized by fast queries that read or write a small number of records, usually indexed by key. See “Transaction Processing or Analytics?” .

在线事务处理。访问模式特征为快速查询读取或写入数量较少的记录，通常由键索引。请参阅“事务处理还是分析？”。

partitioning

Splitting up a large dataset or computation that is too big for a single machine into smaller parts and spreading them across several machines. Also known as sharding . See Chapter 6 .

将太大无法在单个机器上处理的大型数据集或计算拆分成较小的部分，并将它们分散在多台机器上。也称为分片。请参见第6章。

percentile

A way of measuring the distribution of values by counting how many values are above or below some threshold. For example, the 95th percentile response time during some period is the time t such that 95% of requests in that period complete in less than t , and 5% take longer than t . See “Describing Performance” .

一种通过计算有多少值高于或低于某个阈值来衡量价值分布的方法。例如，在某段时间内，第95个百分位响应时间是时间t，该时间下的请求完成时间少于t的百分之95，而超过t的有5％。请参阅“描述性能”。

primary key

A value (typically a number or a string) that uniquely identifies a record. In many applications, primary keys are generated by the system when a record is created (e.g., sequentially or randomly); they are not usually set by users. See also secondary index .

一个唯一标识记录的值（通常是数字或字符串）。在许多应用程序中，当记录被创建时（例如按顺序或随机），系统会生成主键；它们通常不是由用户设置的。另见二级索引。

quorum

The minimum number of nodes that need to vote on an operation before it can be considered successful. See “Quorums for reading and writing” .

操作被视为成功之前需要投票的最小节点数。请参见“读写配额”。

rebalance

To move data or services from one node to another in order to spread the load fairly. See “Rebalancing Partitions” .

将数据或服务从一个节点移动到另一个节点，以使负载分布更加公平。参见“重新平衡分区”。

replication

Keeping a copy of the same data on several nodes ( replicas ) so that it remains accessible if a node becomes unreachable. See Chapter 5 .

将相同的数据副本存储在多个节点上，以便在一个节点无法访问时仍然可访问。见第五章。

schema

A description of the structure of some data, including its fields and datatypes. Whether some data conforms to a schema can be checked at various points in the data’s lifetime (see “Schema flexibility in the document model” ), and a schema can change over time (see Chapter 4 ).

一些数据的结构描述，包括其字段和数据类型。可以在数据的生命周期的各个阶段检查某些数据是否符合模式（请参见“文档模型中的模式灵活性”），并且模式可以随时间改变（请参见第四章）。

secondary index

An additional data structure that is maintained alongside the primary data storage and which allows you to efficiently search for records that match a certain kind of condition. See “Other Indexing Structures” and “Partitioning and Secondary Indexes” .

附加的数据结构同时维护在主数据存储之外，能够帮助你高效地搜索符合某种条件的记录。请参见“其他索引结构”和“分区和二级索引”。

serializable

A guarantee that if several transactions execute concurrently, they behave the same as if they had executed one at a time, in some serial order. See “Serializability” .

如果多个事务同时执行，有一个保证它们的行为就像它们一个接一个地按照某种顺序执行一样。请参见“串行化”。

shared-nothing

An architecture in which independent nodes—each with their own CPUs, memory, and disks—are connected via a conventional network, in contrast to shared-memory or shared-disk architectures. See the introduction to Part II .

一种体系结构，其中独立的节点——每个节点都有自己的CPU、内存和磁盘——通过传统网络连接，与共享内存或共享磁盘体系结构相反。请参阅第II部分的介绍。

skew

1. Imbalanced load across partitions, such that some partitions have lots of requests or data, and others have much less. Also known as hot spots . See “Skewed Workloads and Relieving Hot Spots” and “Handling skew” .

   分区之间的负载不平衡，导致一些分区有大量请求或数据，其他分区则较少。也称为热点。请参见“倾斜工作负载和缓解热点”和“处理倾斜”。

2. A timing anomaly that causes events to appear in an unexpected, nonsequential order. See the discussions of read skew in “Snapshot Isolation and Repeatable Read” , write skew in “Write Skew and Phantoms” , and clock skew in “Timestamps for ordering events” .

   时间异常导致事件以意外的非顺序方式出现。请参阅“快照隔离和可重复读”中关于读取偏斜的讨论，“写偏斜和幻影”中关于写入偏斜的讨论，以及“事件排序的时间戳”中关于时钟偏差的讨论。

split brain

A scenario in which two nodes simultaneously believe themselves to be the leader, and which may cause system guarantees to be violated. See “Handling Node Outages” and “The Truth Is Defined by the Majority” .

两个节点同时认为自己是领导者的情况可能会导致系统保障被违反。请参见“处理节点故障”和“真相由多数决定”。

stored procedure

A way of encoding the logic of a transaction such that it can be entirely executed on a database server, without communicating back and forth with a client during the transaction. See “Actual Serial Execution” .

一种编码事务逻辑的方式，使其可以完全在数据库服务器上执行，而无需在事务期间与客户端来回通信。参见“实际串行执行”。

stream process

A continually running computation that consumes a never-ending stream of events as input, and derives some output from it. See Chapter 11 .

一个持续运行的计算，消耗无止境的事件流作为输入，并从中派生一些输出。请参阅第11章。

synchronous

The opposite of asynchronous .

同步的。

system of record

A system that holds the primary, authoritative version of some data, also known as the source of truth . Changes are first written here, and other datasets may be derived from the system of record. See the introduction to Part III .

一个持有某些数据主要权威版本，也被称为真相来源的系统。更改首先在此处书写，其他数据集可以派生自记录系统。请参见第三部分的介绍。

timeout

One of the simplest ways of detecting a fault, namely by observing the lack of a response within some amount of time. However, it is impossible to know whether a timeout is due to a problem with the remote node, or an issue in the network. See “Timeouts and Unbounded Delays” .

其中一种最简单的检测故障的方法是观察在某段时间内未收到响应。但是，无法确定超时是由远程节点的问题还是网络问题导致。请参阅《超时和无界延迟》。

total order

A way of comparing things (e.g., timestamps) that allows you to always say which one of two things is greater and which one is lesser. An ordering in which some things are incomparable (you cannot say which is greater or smaller) is called a partial order . See “The causal order is not a total order” .

一种比较事物（例如时间戳）的方法，使您始终可以说出两个事物中哪一个更大或更小。一种排序，其中某些事物是无法比较的（您无法说哪一个更大或更小），被称为偏序。请参见“因果关系不是完全排序”。

transaction

Grouping together several reads and writes into a logical unit, in order to simplify error handling and concurrency issues. See Chapter 7 .

将几次读写操作归为一个逻辑单元，以简化错误处理和并发问题。详见第七章。

two-phase commit (2PC)

An algorithm to ensure that several database nodes either all commit or all abort a transaction. See “Atomic Commit and Two-Phase Commit (2PC)” .

一个算法，确保多个数据库节点要么全部提交要么全部撤回一个事务。参见“原子提交和两阶段提交（2PC）”。

two-phase locking (2PL)

An algorithm for achieving serializable isolation that works by a transaction acquiring a lock on all data it reads or writes, and holding the lock until the end of the transaction. See “Two-Phase Locking (2PL)” .

一种实现可串行隔离的算法，其原理是事务在读取或写入数据时需获取锁，并在事务结束之前一直持有该锁。参考“两阶段锁定（2PL）”。

unbounded

Not having any known upper limit or size. The opposite of bounded .

没有任何已知的上限或大小。与有界相反。

Index