俗语

The MongoDB aggregation framework provides a means to calculate aggregate values without having to use map-reduce.

A member of a replica set that exists solely to vote in elections. Arbiters do not replicate data.

A serialization format used to store documents and make remote procedure calls in MongoDB. “BSON” is a portmanteau of the words “binary” and “JSON”. Think of BSON as a binary representation of JSON (JavaScript Object Notation) documents. For a detailed spec, see bsonspec.org.

The set of types supported by the BSON serialization format. The following types are available:

A fixed-sized collection. Once they reach their fixed size, capped collections automatically overwrite their oldest entries. MongoDB’s oplog replication mechanism depends on capped collections. Developers may also use capped collections in their applications.

Collections are groupings of BSON documents. Collections do not enforce a schema, but they are otherwise mostly analogous to RDBMS tables.

The documents within a collection may not need the exact same set of fields, but typically all documents in a collection have a similar or related purpose for an application.

All collections exist within a single database. The namespace within a database for collections are flat.

See What is a namespace in MongoDB? and BSON 文档 for more information.

A property that allows clients to address members in a system to based upon their location.

Replica sets implement data-center awareness using tagging. See 数据中心意识 for more information.

Any MongoDB operation other than an insert, update, remove, or query. MongoDB exposes commands as queries against the special $cmd collection. For example, the implementation of count for MongoDB is a command.

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.

Refers to the location of MongoDB’s data file storage. The default dbpath is /data/db. Other common data paths include /srv/mongodb and /var/lib/mongodb.

A member of a replica set that cannot become primary and applies operations at a specified delay. This delay is useful for protecting data from human error (i.e. unintentionally deleted databases) or updates that have unforeseen effects on the production database.

mongod can create a verbose log of operations with the mongod --diaglog option or through the diagLogging command. The mongod creates this log in the directory specified to mongod --dbpath. The name of the is diaglog.<time in hex>, where “<time-in-hex>” reflects the initiation time of logging as a hexadecimal string.

MongoDB uses the dot notation to access the elements of an array and to access the fields of a subdocument.

To access an element of an array by the zero-based index position, you concatenate the array name with the dot (.) and zero-based index position:

'<array>.<index>'

To access a field of a subdocument with dot-notation, you concatenate the subdocument name with the dot (.) and the field name:

'<subdocument>.<field>'

The process of removing or “shedding” chunks from one shard to another. Administrators must drain shards before removing them from the cluster.

A client implementing the communication protocol required for talking to a server. The MongoDB drivers provide language-idiomatic methods for interfacing with MongoDB.

In the context of replica sets, an election is the process by which members of a replica set select primaries on startup and in the event of failures.

In the context of the aggregation framework, expressions are the stateless transformations that operate on the data that passes through the pipeline.

The process that allows one of the secondary members in a replica set to become primary in the event of a failure.

A convention for storing large files in a MongoDB database. All of the official MongoDB drivers support this convention, as does the mongofiles program.

In the context of geospatial queries, haystack indexes enhance searches by creating “bucket” of objects grouped by a second criterion. For example, you might want all geographical searches to also include the type of location being searched for. In this case, you can create a haystack index that includes a document’s position and type:

db.places.ensureIndex( { position: "geoHaystack", type: 1 } )

You can then query on position and type:

db.places.find( { position: [34.2, 33.3], type: "restaurant" } )

A member of a replica set that cannot become primary and is not advertised as part of the set in the database command isMaster, which prevents it from receiving read-only queries depending on read preference.

A sequential, binary transaction used to bring the database into a consistent state in the event of a hard shutdown. MongoDB enables journaling by default for 64-bit builds of MongoDB version 2.0 and newer. Journal files are pre-allocated and will exist as three 1GB file in the data directory. To make journal files smaller, use smallfiles.

When enabled, MongoDB writes data first to the journal and after to the core data files. MongoDB commits to the journal every 100ms and this is configurable using the journalCommitInterval runtime option.

To force mongod to commit to the journal more frequently, you can specify j:true. When a write operation with j:true pending, mongod will reduce journalCommitInterval to a third of the set value.

A JSON document is a collection of fields and values in a structured format. The following is a sample JSON document with two fields:

{ name: "MongoDB",
  type: "database" }

A data and 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.

The MongoDB Shell. mongo connects to mongod and mongos instances, allowing administration, management, and testing. mongo has a JavaScript interface.

The program implementing the MongoDB database server. This server typically runs as a daemon.

The routing and load balancing process that acts an interface between an application and a MongoDB sharded cluster.

The order in which a database stores documents on disk. Typically, the order of documents on disks reflects insertion order, except when documents move internal because of document growth due to update operations. However, Capped collections guarantee that insertion order and natural order are identical.

When you execute find() with no parameters, the database returns documents in forward natural order. When you execute find() and include sort() with a parameter of $natural:-1, the database returns documents in reverse natural order.

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.

Query plan that returns results in the order consistent with the sort() order.

The event that occurs when a process requests stored data (i.e. a page) from memory that the operating system has moved to disk.

The series of operations in the aggregation process.

A per-collection setting that changes and normalizes the way that MongoDB allocates space for each document in an effort to maximize storage reuse reduce fragmentation. This is the default for TTL Collections. See collMod and usePowerOf2Sizes for more information.

2.2 新版功能.

In the context of replica sets, priority is a configurable value that helps determine which members in a replica set are most likely to become primary.

For each query, the MongoDB query optimizer generates a query plan that matches the query to the index that produces the fastest results. The optimizer then uses the query plan each time the mongod receives the query. If a collection changes significantly, the optimizer creates a new query plan.

A setting on the MongoDB drivers that determines how the clients direct read operations. Read preference affects all replica sets including shards. By default, drivers direct all reads to primaries for strict consistency. However, you may also direct reads to secondaries for eventually consistent reads.

The precursor to the MongoDB replica sets.

1.6 版后已移除.

A cluster of MongoDB servers that implements master-slave replication and automated failover. MongoDB’s recommended replication strategy.

A feature allowing multiple database servers to share the same data, thereby ensuring redundancy and facilitating load balancing. MongoDB supports two flavors of replication: master-slave replication and replica sets.

也可以参考

replica set, sharding, 副本集. and 副本集基本概念.

The length of time between the last operation in the primary’s oplog last operation applied to a particular secondary or slave. In general, you want to keep replication lag as small as possible.

In the context of a replica set, the set name refers to an arbitrary name given to a replica set when it’s first configured. All members of a replica set must have the same name specified with the replSet setting (or --replSet option for mongod.)

A single replica set that stores some portion of a sharded cluster’s total data set. See sharding.

The set of nodes comprising a sharded MongoDB deployment. A sharded cluster consists of three config processes, one or more replica sets, and one or more mongos routing processes.

A database architecture that enable horizontal scaling by splitting data into key ranges among two or more replica sets. This architecture is also known as “range-based partitioning.” See shard.

A number of database commands have “helper” methods in the mongo shell that provide a more concise syntax and improve the general interactive experience.

The replica set operation where members replicate data from the primary. Replica sets synchronize data at two different points:

• Initial sync occurs when MongoDB creates new databases on a new or restored replica set member, populating the the member with the replica set’s data.
• “Replication” occurs continually after initial sync and keeps the member updated with changes to the replica set’s data.

Query plan that returns results in an order inconsistent with the sort() order.

Specifies whether a write operation has succeeded. Write concern allows your application to detect insertion errors or unavailable mongod instances. For replica sets, you can configure write concern to confirm replication to a specified number of members.