Glossary术语汇编

$cmd
A special virtual collection that exposes MongoDB’s database commands. 一个特殊的虚拟集合，公开MongoDB的数据库命令。To use database commands, see Issue Commands.要使用数据库命令，请参阅发布命令。
_id
A field required in every MongoDB document. 每个MongoDB文档中都需要一个字段。The _id field must have a unique value. _id字段必须具有唯一的值。You can think of the _id field as the document’s primary key. 可以将_id字段视为文档的主键。If you create a new document without an _id field, MongoDB automatically creates the field and assigns a unique BSON ObjectId.如果创建一个没有_id字段的新文档，MongoDB会自动创建该字段并分配一个唯一的BSON ObjectId。
accumulator累加器
An expression in the aggregation framework that maintains state between documents in the aggregation pipeline. 聚合框架中的一个表达式，用于维护聚合管道中文档之间的状态。For a list of accumulator operations, see $group.有关累加器操作的列表，请参阅$group。
action动作
An operation the user can perform on a resource. 用户可以对资源执行的操作。Actions and resources combine to create privileges. 操作和资源结合起来创建权限。See action.请参阅操作。
admin database管理数据库
A privileged database. 特权数据库。Users must have access to the admin database to run certain administrative commands. 用户必须访问admin数据库才能运行某些管理命令。For a list of administrative commands, see Administration Commands.有关管理命令的列表，请参阅管理命令。
aggregation聚集
Any of a variety of operations that reduces and summarizes large sets of data. 减少和汇总大量数据的各种操作。MongoDB’s aggregate() and mapReduce() methods are two examples of aggregation operations. MongoDB的aggregate()和mapReduce()方法是聚合操作的两个示例。For more information, see Aggregation.有关更多信息，请参阅聚合。
aggregation framework聚合框架
The set of MongoDB operators that let you calculate aggregate values without having to use map-reduce. MongoDB运算符集，允许您计算聚合值，而无需使用map-reduce。For a list of operators, see Aggregation Reference.有关运算符列表，请参阅聚合参考。
arbiter仲裁人
A member of a replica set that exists solely to vote in elections. 仅为在选举中投票而存在的复制集的成员。Arbiters do not replicate data. 仲裁者不会复制数据。See Replica Set Arbiter.请参阅副本集仲裁器。
Atlas
MongoDB Atlas is a cloud-hosted database-as-a-service.是一个云托管的数据库即服务。
authentication身份验证
Verification of the user identity. 验证用户身份。See Authentication.请参阅身份验证。
authorization授权
Provisioning of access to databases and operations. 提供对数据库和操作的访问。See Role-Based Access Control.请参阅基于角色的访问控制。
B-tree
A data structure commonly used by database management systems to store indexes. 数据库管理系统常用于存储索引的数据结构。MongoDB uses B-trees for its indexes.MongoDB使用B树作为索引。
balancer平衡器
An internal MongoDB process that runs in the context of a sharded cluster and manages the migration of chunks. 一个内部MongoDB进程，在分片集群的上下文中运行，并管理块的迁移。Administrators must disable the balancer for all maintenance operations on a sharded cluster. 管理员必须为分片群集上的所有维护操作禁用平衡器。See Sharded Cluster Balancer.请参阅分片群集平衡器。
BSON
A serialization format used to store documents and make remote procedure calls in MongoDB. 一种序列化格式，用于在MongoDB中存储文档和进行远程过程调用。“BSON” is a portmanteau of the words “binary” and “JSON”. “BSON”是“二进制”和“JSON”的组合。Think of BSON as a binary representation of JSON (JavaScript Object Notation) documents. 可以将BSON看作JSON（JavaScript对象表示法）文档的二进制表示。See BSON Types and MongoDB Extended JSON (v2).请参阅BSON类型和MongoDB扩展JSON(v2)。
BSON types类型
The set of types supported by the BSON serialization format. BSON序列化格式支持的类型集。For a list of BSON types, see BSON Types.有关BSON类型的列表，请参阅BSON类型。
CAP Theorem定理
Given three properties of computing systems, consistency, availability, and partition tolerance, a distributed computing system can provide any two of these features, but never all three.考虑到计算系统的三个属性：一致性、可用性和分区容限，分布式计算系统可以提供其中任意两个功能，但不能同时提供这三个功能。
capped collection封顶集合
A fixed-sized collection that automatically overwrites its oldest entries when it reaches its maximum size. 一个固定大小的集合，当其达到最大大小时自动覆盖其最早的条目。The MongoDB oplog that is used in replication is a capped collection. 复制中使用的MongoDB oplog是一个有上限的集合。See Capped Collections.请参阅封顶集合。
cardinality
The measure of the number of elements within a set of values. 一组值中元素数量的度量。For example, the set A = { 2, 4, 6 } contains 3 elements, and has a cardinality of 3. 例如，集合A = { 2, 4, 6 }包含3个元素，基数为3。See Shard Key Cardinality.请参见Shard Key基数。
checksum
A calculated value used to ensure data integrity. 用于确保数据完整性的计算值。The md5 algorithm is sometimes used as a checksum.md5算法有时用作校验和。
chunk
A contiguous range of shard key values within a particular shard. Chunk ranges are inclusive of the lower boundary and exclusive of the upper boundary. MongoDB splits chunks when they grow beyond the configured chunk size, which by default is 64 megabytes. MongoDB migrates chunks when a shard contains too many chunks of a collection relative to other shards. See Data Partitioning with Chunks and Sharded Cluster Balancer.
client

The application layer that uses a database for data persistence and storage. 使用数据库进行数据持久化和存储的应用层。Drivers provide the interface level between the application layer and the database server.驱动程序提供应用程序层和数据库服务器之间的接口级别。

Client can also refer to a single thread or process.客户端还可以引用单个线程或进程。

cluster
See sharded cluster.请参阅分片群集。
collection集合
A grouping of MongoDB documents. MongoDB文档的一组。A collection is the equivalent of an RDBMS table. 集合相当于一个RDBMS表。A collection exists within a single database. 集合存在于单个数据库中。Collections do not enforce a schema. 集合不强制架构。Documents within a collection can have different fields. 集合中的文档可以有不同的字段。Typically, all documents in a collection have a similar or related purpose. 通常，集合中的所有文档都有类似或相关的用途。See Namespaces.请参阅名称空间。
collection scan集合扫描
Collection scans are a query execution strategy where MongoDB must inspect every document in a collection to see if it matches the query criteria. 集合扫描是一种查询执行策略，MongoDB必须检查集合中的每个文档，看看它是否符合查询条件。These queries are very inefficient and do not use indexes. 这些查询效率很低，而且不使用索引。See Query Optimization for details about query execution strategies.有关查询执行策略的详细信息，请参阅查询优化。
compound index复合指数
An index consisting of two or more keys. 由两个或多个键组成的索引。See Compound Indexes.请参阅复合索引。
concurrency control并发控制
Concurrency control ensures that database operations can be executed concurrently without compromising correctness. 并发控制确保数据库操作可以在不影响正确性的情况下并发执行。Pessimistic concurrency control, such as used in systems with locks, will block any potentially conflicting operations even if they may not turn out to actually conflict. Optimistic concurrency control, the approach used by WiredTiger, will delay checking until after a conflict may have occurred, aborting and retrying one of the operations involved in any write conflict that arises.
config database配置数据库
An internal database that holds the metadata associated with a sharded cluster. Applications and administrators should not modify the config database in the course of normal operation. See Config Database.
config server
A mongod instance that stores all the metadata associated with a sharded cluster. See Config Servers.
container
A collected set of software and its dependent libraries that are packaged together to make transferring between computing environments easier. 一组收集的软件及其相关库，它们打包在一起，使计算环境之间的传输更容易。Containers run as compartmentalized processes on your operating system, and can be given their own resource constraints. 容器在您的操作系统上作为分隔的进程运行，并且可以被赋予它们自己的资源约束。Common container technologies are Docker and Kubernetes.常见的容器技术是Docker和Kubernetes。
CRUD
An acronym for the fundamental operations of a database: Create, Read, Update, and Delete. 数据库基本操作的缩写：创建、读取、更新和删除。See MongoDB CRUD Operations.请参阅MongoDB CRUD操作。
CSV
A text-based data format consisting of comma-separated values. 一种基于文本的数据格式，由逗号分隔的值组成。This format is commonly used to exchange data between relational databases since the format is well-suited to tabular data. You can import CSV files using mongoimport.
cursor
A pointer to the result set of a query. Clients can iterate through a cursor to retrieve results. By default, cursors timeout after 10 minutes of inactivity. See Iterate a Cursor in the mongo Shell.
daemon
The conventional name for a background, non-interactive process.非交互式后台进程的传统名称。
data directory
The file-system location where the mongod stores data files. The dbPath option specifies the data directory.
data partition
A distributed system architecture that splits data into ranges. 一种将数据分成多个范围的分布式系统架构。Sharding uses partitioning. See Data Partitioning with Chunks.
data-center awareness数据中心意识
A property that allows clients to address members in a system based on their locations. 一种属性，允许客户端根据成员的位置向系统中的成员发送地址。Replica sets implement data-center awareness using tagging. See Data Center Awareness.
database
A physical container for collections. Each database gets its own set of files on the file system. A single MongoDB server typically has multiple databases.
database command
A MongoDB operation, other than an insert, update, remove, or query. For a list of database commands, see Database Commands. To use database commands, see Issue Commands.
database profiler
A tool that, when enabled, keeps a record on all long-running operations in a database’s system.profile collection. The profiler is most often used to diagnose slow queries. See Database Profiling.
dbpath
The location of MongoDB’s data file storage. See dbPath.
delayed member
A replica set member that cannot become primary and applies operations at a specified delay. The delay is useful for protecting data from human error (i.e. unintentionally deleted databases) or updates that have unforeseen effects on the production database. See Delayed Replica Set Members.
document
A record in a MongoDB collection and the basic unit of data in MongoDB. Documents are analogous to JSON objects but exist in the database in a more type-rich format known as BSON. See Documents.
dot notation
MongoDB uses the dot notation to access the elements of an array and to access the fields of an embedded document. See Dot Notation.
draining
The process of removing or “shedding” chunks from one shard to another. Administrators must drain shards before removing them from the cluster. See Remove Shards from an Existing Sharded Cluster.
driver
A client library for interacting with MongoDB in a particular language. See /drivers.
durable
A write operation is durable when it will persist across a shutdown (or crash) and restart of one or more server processes. For a single mongod server, a write operation is considered durable when it has been written to the server’s journal file. For a replica set, a write operation is considered durable once the write operation is durable on a majority of voting nodes; i.e. written to a majority of voting nodes’ journals.
election
The process by which members of a replica set select a primary on startup and in the event of a failure. See Replica Set Elections.
eventual consistency
A property of a distributed system that allows changes to the system to propagate gradually. In a database system, this means that readable members are not required to reflect the latest writes at all times.
expression
In the context of aggregation framework, expressions are the stateless transformations that operate on the data that passes through a pipeline. See Aggregation Pipeline.
failover
The process that allows a secondary member of a replica set to become primary in the event of a failure. See Automatic Failover.
field
A name-value pair in a document. 文档中的名称-值对。A document has zero or more fields. 文档有零个或多个字段。Fields are analogous to columns in relational databases. 字段类似于关系数据库中的列。See Document Structure.请参阅文档结构。
field path
Path to a field in the document. 文档中某个字段的路径。To specify a field path, use a string that prefixes the field name with a dollar sign ($).要指定字段路径，请使用以美元符号（$）作为字段名前缀的字符串。
firewall
A system level networking filter that restricts access based on, among other things, IP address. 一个系统级网络筛选器，根据IP地址等限制访问。Firewalls form a part of an effective network security strategy. 防火墙是有效网络安全策略的一部分。See Firewalls.请参阅防火墙。
fsync
A system call that flushes all dirty, in-memory pages to disk. 一种系统调用，将所有脏的内存页刷新到磁盘。MongoDB calls fsync() on its database files at least every 60 seconds. MongoDB至少每60秒对其数据库文件调用一次fsync()。See fsync.请参阅fsync。
geohash
A geohash value is a binary representation of the location on a coordinate grid. geohash值是坐标网格上位置的二进制表示。See Calculation of Geohash Values for 2d Indexes.请参见2d索引的Geohash值计算。
GeoJSON
A geospatial data interchange format based on JavaScript Object Notation (JSON). GeoJSON is used in geospatial queries. For supported GeoJSON objects, see Geospatial Data. For the GeoJSON format specification, see https://tools.ietf.org/html/rfc7946#section-3.1.
geospatial
Relating to geographical location. 与地理位置有关的。See Geospatial Queries.请参见地理空间查询。
GridFS
A convention for storing large files in a MongoDB database. 在MongoDB数据库中存储大型文件的约定。All of the official MongoDB drivers support this convention, as does the mongofiles program. 所有官方MongoDB驱动程序都支持这种约定，mongofiles程序也是如此。See GridFS.请参阅GridFS。
hashed shard key
A special type of shard key that uses a hash of the value in the shard key field to distribute documents among members of the sharded cluster. See Hashed Indexes.
haystack index
A geospatial index that enhances searches by creating “buckets” of objects grouped by a second criterion. See geoHaystack Indexes.
hidden member
A replica set member that cannot become primary and are invisible to client applications. See Hidden Replica Set Members.
high availability

High availability indicates a system designed for durability, redundancy, and automatic failover such that the applications supported by the system can operate continuously and without downtime for a long period of time. 高可用性指的是一个为持久性、冗余性和自动故障切换而设计的系统，这样系统支持的应用程序可以连续运行，并且不会长时间停机。MongoDB replica sets support high availability when deployed according to our documented best practices.

For guidance on replica set deployment architecture, see Replica Set Deployment Architectures.

idempotent
The quality of an operation to produce the same result given the same input, whether run once or run multiple times.在相同的输入下产生相同结果的操作的质量，无论是运行一次还是多次。
index
A data structure that optimizes queries. 优化查询的数据结构。See Indexes.请参阅索引。
init script
A simple shell script used by a Linux platform’s init system to start, restart, or stop a daemon process. If you installed MongoDB via a package manager, an init script has been provided for your system as part of the installation. See the respective Installation Guide for your operating system.
init system
The init system is the first process started on a Linux platform after the kernel starts, and manages all other processes on the system. init系统是内核启动后在Linux平台上启动的第一个进程，它管理系统上的所有其他进程。The init system uses an init script to start, restart, or stop a daemon process, such as mongod or mongos. Recent versions of Linux tend to use the systemd init system, which uses the systemctl command, while older versions tend to use the System V init system, which uses the service command. See the respective Installation Guide for your operating system.
initial sync
The replica set operation that replicates data from an existing replica set member to a new replica set member. See Initial Sync.
intent lock
A lock on a resource that indicates that the holder of the lock will read (intent shared) or write (intent exclusive) the resource using concurrency control at a finer granularity than that of the resource with the intent lock. Intent locks allow concurrent readers and writers of a resource. See What type of locking does MongoDB use?.
interrupt point
A point in an operation’s lifecycle when it can safely abort. 操作生命周期中可以安全中止的点。MongoDB only terminates an operation at designated interrupt points. MongoDB只在指定的中断点终止操作。See Terminate Running Operations.请参阅终止运行操作。
IPv6
A revision to the IP (Internet Protocol) standard that provides a significantly larger address space to more effectively support the number of hosts on the contemporary Internet.对IP（互联网协议）标准的修订，提供了更大的地址空间，以更有效地支持当代互联网上的主机数量。
ISODate
The international date format used by mongo to display dates. The format is: YYYY-MM-DD HH:MM.SS.millis.
JavaScript
A popular scripting language originally designed for web browsers. 最初为web浏览器设计的一种流行脚本语言。The MongoDB shell and certain server-side functions use a JavaScript interpreter. MongoDB shell和某些服务器端函数使用JavaScript解释器。See Server-side JavaScript for more information.有关更多信息，请参阅服务器端JavaScript。
journal
A sequential, binary transaction log used to bring the database into a valid state in the event of a hard shutdown. Journaling writes data first to the journal and then to the core data files. MongoDB enables journaling by default for 64-bit builds of MongoDB version 2.0 and newer. Journal files are pre-allocated and exist as files in the data directory. See Journaling.
JSON
JavaScript Object Notation. A human-readable, plain text format for expressing structured data with support in many programming languages. For more information, see http://www.json.org. Certain MongoDB tools render an approximation of MongoDB BSON documents in JSON format. See MongoDB Extended JSON (v2).
JSON document
A JSON document is a collection of fields and values in a structured format. For sample JSON documents, see http://json.org/example.html.
JSONP
JSON with Padding. Refers to a method of injecting JSON into applications. Presents potential security concerns.
least privilege
An authorization policy that gives a user only the amount of access that is essential to that user’s work and no more.
legacy coordinate pairs
The format used for geospatial data prior to MongoDB version 2.4. This format stores geospatial data as points on a planar coordinate system (e.g. [ x, y ]). See Geospatial Queries.
LineString
A LineString is defined by an array of two or more positions. A closed LineString with four or more positions is called a LinearRing, as described in the GeoJSON LineString specification: https://tools.ietf.org/html/rfc7946#section-3.1.4. To use a LineString in MongoDB, see GeoJSON Objects.
lock
MongoDB uses locks to ensure that concurrency does not affect correctness. MongoDB uses read locks, write locks and intent locks. For more information, see What type of locking does MongoDB use?.
LVM
Logical volume manager. LVM is a program that abstracts disk images from physical devices and provides a number of raw disk manipulation and snapshot capabilities useful for system management. For information on LVM and MongoDB, see Back Up and Restore Using LVM on Linux.
map-reduce
A data processing and aggregation paradigm consisting of a “map” phase that selects data and a “reduce” phase that transforms the data. In MongoDB, you can run arbitrary aggregations over data using map-reduce. For map-reduce implementation, see Map-Reduce. For all approaches to aggregation, see Aggregation.
mapping type
A Structure in programming languages that associate keys with values, where keys may nest other pairs of keys and values (e.g. dictionaries, hashes, maps, and associative arrays). The properties of these structures depend on the language specification and implementation. Generally the order of keys in mapping types is arbitrary and not guaranteed.
md5
A hashing algorithm used to efficiently provide reproducible unique strings to identify and checksum data. MongoDB uses md5 to identify chunks of data for GridFS. See filemd5.
MIB
Management Information Base. MongoDB uses MIB files to define the type of data tracked by SNMP in the MongoDB Enterprise edition.
MIME
Multipurpose Internet Mail Extensions. A standard set of type and encoding definitions used to declare the encoding and type of data in multiple data storage, transmission, and email contexts. The mongofiles tool provides an option to specify a MIME type to describe a file inserted into GridFS storage.
mongo
The MongoDB shell. The mongo process starts the MongoDB shell as a daemon connected to either a mongod or mongos instance. The shell has a JavaScript interface. See mongo and mongo Shell Methods.
mongod
The MongoDB database server. The mongod process starts the MongoDB server as a daemon. The MongoDB server manages data requests and formats and manages background operations. See mongod.
mongos
The MongoDB sharded cluster query router. The mongos process starts the MongoDB router as a daemon. The MongoDB router acts as an interface between an application and a MongoDB sharded cluster and handles all routing and load balancing across the cluster. See mongos.
namespace
The canonical name for a collection or index in MongoDB. The namespace is a combination of the database name and the name of the collection or index, like so: [database-name].[collection-or-index-name]. All documents belong to a namespace. See Namespaces.
natural order
The order in which the database refers to documents on disk. This is the default sort order. See $natural and Return in Natural Order.
network partition

A network failure that separates a distributed system into partitions such that nodes in one partition cannot communicate with the nodes in the other partition.

Sometimes, partitions are partial or asymmetric. An example of a partial partition would be a division of the nodes of a network into three sets, where members of the first set cannot communicate with members of the second set, and vice versa, but all nodes can communicate with members of the third set. In an asymmetric partition, communication may be possible only when it originates with certain nodes. For example, nodes on one side of the partition can communicate to the other side only if they originate the communications channel.

ObjectId

A special BSON type that guarantees uniqueness within the collection. ObjectId values are 12 bytes in length, consisting of:

  • a 4-byte timestamp value, representing the ObjectId’s creation, measured in seconds since the Unix epoch
  • a 5-byte random value
  • a 3-byte incrementing counter, initialized to a random value

While the BSON format itself is little-endian, the timestamp and counter values are big-endian, with the most significant bytes appearing first in the byte sequence.

See ObjectId for BSON-specific information.

operator
A keyword beginning with a $ used to express an update, complex query, or data transformation. For example, $gt is the query language’s “greater than” operator. For available operators, see Operators.
oplog
A capped collection that stores an ordered history of logical writes to a MongoDB database. The oplog is the basic mechanism enabling replication in MongoDB. See Replica Set Oplog.
optime

Changed in version 3.2.在版本3.2中更改。The following describes the optime format used by protocolVersion: 1, introduced in MongoDB 3.2.

A reference to a position in the replication oplog. The optime value is a document that contains:

  • ts, the Timestamp of the operation.
  • t, the term in which the operation was originally generated on the primary.
ordered query plan
A query plan that returns results in the order consistent with the sort() order. See Query Plans.
orphaned document

In a sharded cluster, orphaned documents are those documents on a shard that also exist in chunks on other shards as a result of failed migrations or incomplete migration cleanup due to abnormal shutdown.

Starting in MongoDB 4.4, orphaned documents are cleaned up automatically after a chunk migration completes. You no longer need to run cleanupOrphaned to delete orphaned documents.

passive member
A member of a replica set that cannot become primary because its members[n].priority is 0. See Priority 0 Replica Set Members.
PID
A process identifier. UNIX-like systems assign a unique-integer PID to each running process. You can use a PID to inspect a running process and send signals to it. See /proc File System.
pipe
A communication channel in UNIX-like systems allowing independent processes to send and receive data. In the UNIX shell, piped operations allow users to direct the output of one command into the input of another.
pipeline
A series of operations in an aggregation process. See Aggregation Pipeline.
Point
A single coordinate pair as described in the GeoJSON Point specification: https://tools.ietf.org/html/rfc7946#section-3.1.2. To use a Point in MongoDB, see GeoJSON Objects.
Polygon

An array of LinearRing coordinate arrays, as described in the GeoJSON Polygon specification: https://tools.ietf.org/html/rfc7946#section-3.1.6. For Polygons with multiple rings, the first must be the exterior ring and any others must be interior rings or holes.

MongoDB does not permit the exterior ring to self-intersect. Interior rings must be fully contained within the outer loop and cannot intersect or overlap with each other. See GeoJSON Objects.

powerOf2Sizes
A per-collection setting that changes and normalizes the way MongoDB allocates space for each document, in an effort to maximize storage reuse and to reduce fragmentation. This is the default for TTL Collections. See collMod and usePowerOf2Sizes.
pre-splitting
An operation performed before inserting data that divides the range of possible shard key values into chunks to facilitate easy insertion and high write throughput. In some cases pre-splitting expedites the initial distribution of documents in sharded cluster by manually dividing the collection rather than waiting for the MongoDB balancer to do so. See Create Chunks in a Sharded Cluster.
prefix compression
Reduces memory and disk consumption by storing any identical index key prefixes only once, per page of memory. See: Compression for more about WiredTiger’s compression behavior.
primary
In a replica set, the primary is the member that receives all write operations. See Primary.
primary key
A record’s unique immutable identifier. In an RDBMS, the primary key is typically an integer stored in each row’s id field. In MongoDB, the _id field holds a document’s primary key which is usually a BSON ObjectId.
primary shard
The shard that holds all the un-sharded collections. See Primary Shard.
priority
A configurable value that helps determine which members in a replica set are most likely to become primary. See members[n].priority.
privilege
A combination of specified resource and actions permitted on the resource. See privilege.
projection
A document given to a query that specifies which fields MongoDB returns in the result set. See Project Fields to Return from Query. For a list of projection operators, see Projection Operators.
query
A read request. MongoDB uses a JSON-like query language that includes a variety of query operators with names that begin with a $ character. In the mongo shell, you can issue queries using the db.collection.find() and db.collection.findOne() methods. See Query Documents.
query optimizer查询优化器
A process that generates query plans. 生成查询计划的过程。For each query, the optimizer generates a plan that matches the query to the index that will return results as efficiently as possible. 对于每个查询，优化器都会生成一个将查询与索引相匹配的计划，该索引将尽可能高效地返回结果。The optimizer reuses the query plan each time the query runs. 每次查询运行时，优化器都会重用查询计划。If a collection changes significantly, the optimizer creates a new query plan. 如果集合发生显著变化，优化器将创建一个新的查询计划。See Query Plans.请参阅查询计划。
query shape

A combination of query predicate, sort, and projection.查询谓词、排序和投影的组合。

For the query predicate, only the structure of the predicate, including the field names, are significant; the values in the query predicate are insignificant. 对于查询谓词，只有谓词的结构（包括字段名）是重要的；查询谓词中的值无关紧要。As such, a query predicate {type: 'food' } is equivalent to the query predicate { type: 'utensil' } for a query shape.因此，查询谓词{type: 'food' }相当于查询形状的查询谓词{ type: 'utensil' }。

To help identify slow queries with the same query shape, starting in MongoDB 4.2, each query shape is associated with a queryHash. The queryHash is a hexadecimal string that represents a hash of the query shape and is dependent only on the query shape.queryHash是一个十六进制字符串，表示查询形状的散列，并且仅依赖于查询形状。

Note

As with any hash function, two different query shapes may result in the same hash value. 与任何哈希函数一样，两个不同的查询形状可能会产生相同的哈希值。However, the occurrence of hash collisions between different query shapes is unlikely.但是，不同查询形状之间不太可能发生哈希冲突。

RDBMS
Relational Database Management System. 关系数据库管理系统。A database management system based on the relational model, typically using SQL as the query language.基于关系模型的数据库管理系统，通常使用a href="#term-sql">SQL作为查询语言。
read concern
Specifies a level of isolation for read operations. 指定读取操作的隔离级别。For example, you can use read concern to only read data that has propagated to a majority of nodes in a replica set. 例如，可以使用读关注点仅读取已传播到副本集中大多数Node的数据。See Read Concern.请参阅读关注点。
read lock
A shared lock on a resource such as a collection or database that, while held, allows concurrent readers but no writers. See What type of locking does MongoDB use?.
read preference
A setting that determines how clients direct read operations. 确定客户端如何指导读取操作的设置。Read preference affects all replica sets, including shard replica sets. 读取首选项会影响所有副本集，包括碎片副本集。By default, MongoDB directs reads to primaries. However, you may also direct reads to secondaries for eventually consistent reads. See Read Preference.
recovering
A replica set member status indicating that a member is not ready to begin normal activities of a secondary or primary. Recovering members are unavailable for reads.正在恢复的成员无法读取。
replica pairs

The precursor to the MongoDB replica sets.MongoDB副本集的前身。

Deprecated since version 1.6.自1.6版以来已弃用。

replica set副本集
A cluster of MongoDB servers that implements replication and automated failover. 实现复制和自动故障切换的MongoDB服务器集群。MongoDB’s recommended replication strategy. MongoDB推荐的复制策略。See Replication.请参阅复制。
replication复制
A feature allowing multiple database servers to share the same data, thereby ensuring redundancy and facilitating load balancing. 一种允许多个数据库服务器共享相同数据的功能，从而确保冗余并促进负载平衡。See Replication.请参阅复制。
replication lag
The length of time between the last operation in the primary’s oplog and the last operation applied to a particular secondary. In general, you want to keep replication lag as small as possible. See Replication Lag.
resident memory常驻记忆
The subset of an application’s memory currently stored in physical RAM. 当前存储在物理RAM中的应用程序内存的子集。Resident memory is a subset of virtual memory, which includes memory mapped to physical RAM and to disk.常驻内存是虚拟内存的一个子集，包括映射到物理RAM和磁盘的内存。
resource资源
A database, collection, set of collections, or cluster.数据库、集合、集合集或群集。 A privilege permits actions on a specified resource. See resource.
role
A set of privileges that permit actions on specified resources. Roles assigned to a user determine the user’s access to resources and operations. See Security.
rollback回滚
A process that reverts writes operations to ensure the consistency of all replica set members. 一种恢复写入操作以确保所有副本集成员一致性的进程。See Rollbacks During Replica Set Failover.请参阅副本集故障切换期间的回滚。
secondary
A replica set member that replicates the contents of the master database. Secondary members may handle read requests, but only the primary members can handle write operations. See Secondaries.
secondary index二级索引
A database index that improves query performance by minimizing the amount of work that the query engine must perform to fulfill a query. See Indexes.
seed list
A seed list is used by drivers and clients (like the mongo shell) for initial discovery of the replica set configuration. 驱动程序和客户端（如mongo shell）使用种子列表来初始发现副本集配置。Seed lists can be provided as a list of host:port pairs (see Standard Connection String Format or via DNS entries (see DNS Seed List Connection Format).
set name
The arbitrary name given to a replica set. 为复制集指定的任意名称。All members of a replica set must have the same name specified with the replSetName setting or the --replSet option.副本集的所有成员必须具有使用replSetName设置或--replSet选项指定的相同名称。
shard
A single mongod instance or replica set that stores some portion of a sharded cluster’s total data set. In production, all shards should be replica sets. See Shards.
shard key分片键
The field MongoDB uses to distribute documents among members of a sharded cluster. MongoDB用于在分片集群的成员之间分发文档的字段。See Shard Keys.请参阅分片键。
sharded cluster分片群集
The set of nodes comprising a sharded MongoDB deployment. A sharded cluster consists of config servers, shards, and one or more mongos routing processes. See Sharded Cluster Components.
sharding
A database architecture that partitions data by key ranges and distributes the data among two or more database instances. 一种数据库体系结构，它按键范围划分数据，并在两个或多个数据库实例之间分配数据。Sharding enables horizontal scaling. 分片支持水平缩放。See Sharding.请参阅分片。
shell helper
A method in the mongo shell that provides a more concise syntax for a database command. Shell helpers improve the general interactive experience. See mongo Shell Methods.请参阅mongo Shell方法。
single-master replication单主机复制
A replication topology where only a single database instance accepts writes. 只有一个数据库实例接受写入的复制拓扑。Single-master replication ensures consistency and is the replication topology employed by MongoDB. 单主机复制确保了一致性，是MongoDB采用的复制拓扑。See Replica Set Primary.请参阅副本集主副本。
snappy
A compression/decompression library designed to balance efficient computation requirements with reasonable compression rates. 一个压缩/解压库，旨在平衡高效的计算要求和合理的压缩率。Snappy is the default compression library for MongoDB’s use of WiredTiger. Snappy是MongoDB使用WiredTiger的默认压缩库。See Snappy and the WiredTiger compression documentation for more information.有关更多信息，请参阅Snappy和WiredTiger压缩文档。
split
The division between chunks in a sharded cluster. See Data Partitioning with Chunks.请参阅数据块分区。
SQL
Structured Query Language (SQL) is a common special-purpose programming language used for interaction with a relational database, including access control, insertions, updates, queries, and deletions. 结构化查询语言（SQL）是一种常见的专用编程语言，用于与关系数据库进行交互，包括访问控制、插入、更新、查询和删除。There are some similar elements in the basic SQL syntax supported by different database vendors, but most implementations have their own dialects, data types, and interpretations of proposed SQL standards. 不同的数据库供应商支持的基本SQL语法中有一些类似的元素，但大多数实现都有自己的方言、数据类型，以及对建议的SQL标准的解释。Complex SQL is generally not directly portable between major RDBMS products. 复杂的SQL通常不能在主要的RDBMS产品之间直接移植。SQL is often used as metonym for relational databases.SQL经常被用作关系数据库的转喻。
SSD
Solid State Disk. 固态磁盘。A high-performance disk drive that uses solid state electronics for persistence, as opposed to the rotating platters and movable read/write heads used by traditional mechanical hard drives.一种高性能磁盘驱动器，使用固态电子器件进行持久化，与传统机械硬盘驱动器使用的旋转盘片和可移动读/写磁头不同。
standalone
An instance of mongod that is running as a single server and not as part of a replica set. To convert a standalone into a replica set, see Convert a Standalone to a Replica Set.
storage engine
The part of a database that is responsible for managing how data is stored and accessed, both in memory and on disk. 数据库中负责管理如何在内存和磁盘上存储和访问数据的部分。Different storage engines perform better for specific workloads. 不同的存储引擎对于特定的工作负载表现更好。See Storage Engines for specific details on the built-in storage engines in MongoDB.有关MongoDB中内置存储引擎的详细信息，请参阅存储引擎。
storage order
See natural order.请参阅自然秩序。
strict consistency严格一致性
A property of a distributed system requiring that all members always reflect the latest changes to the system. 分布式系统的一种属性，要求所有成员始终反映系统的最新变化。In a database system, this means that any system that can provide data must reflect the latest writes at all times.在数据库系统中，这意味着任何能够提供数据的系统都必须始终反映最新的写操作。
sync
The replica set operation where members replicate data from the primary. Sync first occurs when MongoDB creates or restores a member, which is called initial sync. Sync then occurs continually to keep the member updated with changes to the replica set’s data. 然后会持续进行同步，以使成员随着副本集数据的更改而更新。See Replica Set Data Synchronization.请参阅副本集数据同步。
syslog
On UNIX-like systems, a logging process that provides a uniform standard for servers and processes to submit logging information. 在类UNIX系统上，为服务器和进程提交日志信息提供一致性标准的一种日志记录过程。MongoDB provides an option to send output to the host’s syslog system. MongoDB提供了一个选项，可以将输出发送到主机的syslog系统。See syslogFacility.请参阅syslogFacility。
tag

A label applied to a replica set member and used by clients to issue data-center-aware operations. 应用于副本集成员的标签，客户端使用该标签来执行数据中心感知操作。For more information on using tags with replica sets, see the following sections of this manual: Read Preference Tag Sets.有关将标记与副本集一起使用的更多信息，请参阅本手册的以下章节：阅读首选项标记集。

Changed in version 3.4:In MongoDB 3.4, sharded cluster zones replace tags.

tag set
A document containing zero or more tags.包含零个或多个标记的文档。
tailable cursor可裁剪游标
For a capped collection, a tailable cursor is a cursor that remains open after the client exhausts the results in the initial cursor. 对于封顶集合，可裁剪游标是在客户端耗尽初始游标中的结果后保持打开状态的游标。As clients insert new documents into the capped collection, the tailable cursor continues to retrieve documents.当客户端将新文档插入到capped集合中时，可裁剪游标将继续检索文档。
term
For the members of a replica set, a monotonically increasing number that corresponds to an election attempt.对于复制集的成员，与选举尝试相对应的单调递增的数字。
topology
The state of a deployment of MongoDB instances, including the type of deployment (i.e. standalone, replica set, or sharded cluster) as well as the availability of servers, and the role of each server (i.e. primary, secondary, config server, or mongos.)
TSV
A text-based data format consisting of tab-separated values. 一种基于文本的数据格式，由制表符分隔的值组成。This format is commonly used to exchange data between relational databases, since the format is well-suited to tabular data. 这种格式通常用于在关系数据库之间交换数据，因为这种格式非常适合表格数据。You can import TSV files using mongoimport.
TTL
Stands for “time to live” and represents an expiration time or period for a given piece of information to remain in a cache or other temporary storage before the system deletes it or ages it out. 代表“生存时间”，表示给定信息在系统删除或老化之前保留在缓存或其他临时存储中的过期时间或期限。MongoDB has a TTL collection feature. See Expire Data from Collections by Setting TTL.
unique index
An index that enforces uniqueness for a particular field across a single collection. 在单个集合中强制特定字段唯一性的索引。See Unique Indexes.请参阅唯一索引。
unix epoch
January 1st, 1970 at 00:00:00 UTC. 1970年1月1日协调世界时00:00:00。Commonly used in expressing time, where the number of seconds or milliseconds since this point is counted.常用于表示时间，从这一点算起的秒数或毫秒数。
unordered query plan无序查询计划
A query plan that returns results in an order inconsistent with the sort() order. See Query Plans.
upsert
An option for update operations; e.g. db.collection.update(), db.collection.findAndModify(). If set to true, the update operation will either update the document(s) matched by the specified query or if no documents match, insert a new document. The new document will have the fields indicated in the operation. See Insert a New Document if No Match Exists (Upsert).
virtual memory虚拟内存
An application’s working memory, typically residing on both disk and in physical RAM.应用程序的工作内存，通常位于磁盘和物理RAM中。
WGS84
The default reference system and geodetic datum that MongoDB uses to calculate geometry over an Earth-like sphere for geospatial queries on GeoJSON objects. MongoDB用于计算类地球球体上的几何图形的默认参考系和大地基准，用于对GeoJSON对象进行地理空间查询。See the “EPSG:4326: WGS 84” specification: http://spatialreference.org/ref/epsg/4326/.请参阅“EPSG:4326:WGS 84”规范：http://spatialreference.org/ref/epsg/4326/。
working set
The data that MongoDB uses most often.MongoDB最常使用的数据。
write concern
Specifies whether a write operation has succeeded. 指定写入操作是否已成功。Write concern allows your application to detect insertion errors or unavailable mongod instances. Write concern允许应用程序检测插入错误或不可用的mongod实例。For replica sets, you can configure write concern to confirm replication to a specified number of members. 对于副本集，可以配置写入关注点以确认复制到指定数量的成员。See Write Concern.请参阅写关注点。
write conflict
A situation in which two concurrent operations, at least one of which is a write, attempt to use a resource in a way that would violate constraints imposed by a storage engine using optimistic concurrency control. 两个并发操作（至少其中一个是写操作）试图以违反存储引擎使用乐观并发控制施加的约束的方式使用资源的一种情况。MongoDB will transparently abort and retry one of the conflicting operations.MongoDB将透明地中止并重试其中一个冲突操作。
write lock
An exclusive lock on a resource such as a collection or database. When a process writes to a resource, it takes an exclusive write lock to prevent other processes from writing to or reading from that resource. For more information on locks, see FAQ: Concurrency.
writeBacks
The process within the sharding system that ensures that writes issued to a shard that is not responsible for the relevant chunk get applied to the proper shard. 分片系统中的一个过程，用于确保向不负责相关块的分片发出的写入操作应用于正确的分片。For related information, see What does writebacklisten in the log mean? and writeBacksQueued.有关相关信息，请参阅writebacklisten在日志中是什么意思？以及writeBacksQueued。
zlib
A data compression library that provides higher compression rates at the cost of more CPU, compared to MongoDB’s use of snappy. 与MongoDB使用snappy相比，它是一个以更多CPU为代价提供更高压缩率的数据压缩库。You can configure WiredTiger to use zlib as its compression library. 您可以将WiredTiger配置为使用zlib作为其压缩库。See http://www.zlib.net and the WiredTiger compression documentation for more information.请参阅http://www.zlib.net以及WiredTiger压缩文档以获取更多信息。
zone

New in version 3.4:3.4版中新增：A grouping of documents based on ranges of shard key values for a given sharded collection. 基于给定分片集合的分片键值范围的文档分组。Each shard in the sharded cluster can associate with one or more zones. 分片集群中的每个分片都可以与一个或多个分区关联。In a balanced cluster, MongoDB directs reads and writes covered by a zone only to those shards inside the zone. 在平衡集群中，MongoDB只将区域覆盖的读写操作定向到区域内的碎片。See the Zones manual page for more information.有关更多信息，请参阅区域手册页面。

Zones supersede functionality described by tags in MongoDB 3.2.区域取代MongoDB 3.2中标签描述的功能。

zstd

New in version 4.2.版本4.2中的新功能。

A data compression library that provides higher compression rates and lower CPU usage when compared to zlib.一个数据压缩库，与zlib相比，它提供了更高的压缩率和更低的CPU使用率。