diff --git a/source/reference/glossary.txt b/source/reference/glossary.txt index f5b08d45286..9029c32d322 100644 --- a/source/reference/glossary.txt +++ b/source/reference/glossary.txt @@ -23,7 +23,7 @@ Glossary :sorted: $cmd - A special virtual :term:`collection` that exposes MongoDB's + A virtual :term:`collection` that exposes MongoDB's :term:`database commands `. To use database commands, see :ref:`issue-commands`. @@ -33,7 +33,7 @@ Glossary think of the ``_id`` field as the document's :term:`primary key`. If you create a new document without an ``_id`` field, MongoDB automatically creates the field and assigns a unique - BSON :term:`ObjectId`. + BSON :term:`ObjectId` to the field. accumulator An :term:`expression` in an :term:`aggregation pipeline` that @@ -53,20 +53,23 @@ Glossary see :ref:`admin-commands`. aggregation - Any of a variety of operations that reduces and summarizes large + An operation that reduces and summarizes large sets of data. MongoDB's :method:`~db.collection.aggregate()` and :method:`~db.collection.mapReduce()` methods are two examples of aggregation operations. For more information, see :doc:`/aggregation`. aggregation pipeline - The set of MongoDB operators that let you calculate aggregate - values without having to use :term:`map-reduce`. For a list of - operators, see :doc:`/reference/aggregation`. + Consists of one or more stages that process documents. Aggregation + operators calculate aggregate values without having to use + :term:`map-reduce`. For a list of operators, see + :doc:`/reference/aggregation`. arbiter - A member of a :term:`replica set` that exists solely to vote in - :term:`elections `. Arbiters do not replicate data. See + A :term:`replica set` member that exists just to vote in + :term:`elections `. Arbiters do not replicate data. An + arbiter participates in elections for a :term:`primary` but cannot + become a primary. For more details, see :ref:`replica-set-arbiter-configuration`. Atlas @@ -74,8 +77,8 @@ Glossary is a cloud-hosted database-as-a-service. atomic operation - An atomic operation is a write operation which either completes - entirely, or does not complete at all. In the case of + An atomic operation is a write operation that either completes + entirely or doesn't complete at all. For :ref:`distributed transactions `, which involve writes to multiple documents, all writes to each document must succeed for the transaction to succeed. Atomic operations cannot @@ -101,7 +104,7 @@ Glossary Backup cursors are for internal use only. blocking sort - A sort that must be performed in memory before output is returned. + A sort that must be performed in memory before the output is returned. Blocking sorts may impact performance for large data sets. Use an :term:`indexed sort` to avoid a blocking sort. @@ -110,14 +113,14 @@ Glossary bounded collection scan A plan used by the :doc:`query optimizer ` that - eliminates documents with specific field value ranges. For + excludes documents with specific field value ranges. For example, if a range of date field values is outside of a specified - date range, the documents in that range are eliminated from the + date range, the documents in that range are excluded from the query plan. See :ref:`explain-output-collection-scan`. BSON A serialization format used to store :term:`documents ` and make - remote procedure calls in MongoDB. "BSON" is a portmanteau of the words + remote procedure calls in MongoDB. "BSON" is a combination of the words "binary" and "JSON". Think of BSON as a binary representation of JSON (JavaScript Object Notation) documents. See :doc:`/reference/bson-types` and @@ -129,7 +132,7 @@ Glossary B-tree A data structure commonly used by database management systems to - store indexes. MongoDB uses B-trees for its indexes. + store indexes. MongoDB uses B-tree indexes. CAP Theorem Given three properties of computing systems, consistency, @@ -139,7 +142,7 @@ Glossary capped collection A fixed-sized :term:`collection ` that automatically - overwrites its oldest entries when it reaches its maximum size. + overwrites its oldest entries when the collection reaches its maximum size. The MongoDB :term:`oplog` that is used in :term:`replication` is a capped collection. See :doc:`/core/capped-collections`. @@ -149,11 +152,11 @@ Glossary and has a cardinality of 3. See :ref:`shard-key-cardinality`. cartesian product - The result of combining two data sets such that the combined set + The result of combining two data sets where the combined set contains every possible combination of values. cfq - Complete Fairness Queueing (cfq) is a I/O operation scheduler + Complete Fairness Queueing (cfq) is an I/O operation scheduler that allocates bandwidth for incoming request processes. checksum @@ -161,7 +164,7 @@ Glossary The :term:`md5` algorithm is sometimes used as a checksum. chunk - A contiguous range of :term:`shard key` values within a particular + A contiguous range of :term:`shard key` values within a :term:`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 @@ -174,7 +177,7 @@ Glossary and storage. :term:`Drivers ` provide the interface level between the application layer and the database server. - Client can also refer to a single thread or process. + A client can also be a single thread or process. client affinity A consistent client connection to a specified data source. @@ -188,16 +191,16 @@ Glossary collection A grouping of MongoDB :term:`documents `. A collection - is the equivalent of an :term:`RDBMS` table. A collection exists - within a single :term:`database`. Collections do not enforce a - schema. Documents within a collection can have different fields. - Typically, all documents in a collection have a similar or related + is the equivalent of an :term:`RDBMS` table. A collection is + in a single :term:`database`. Collections do not enforce a + schema. Documents in a collection can have different fields. + Typically, documents in a collection have a similar or related purpose. See :ref:`faq-dev-namespace`. collection scan Collection scans are a query execution strategy where MongoDB must inspect every document in a collection to see if it matches the - query criteria. These queries are very inefficient and do not use + query criteria. These queries are very inefficient and don't use indexes. See :doc:`/core/query-optimization` for details about query execution strategies. @@ -214,20 +217,20 @@ Glossary concurrency control Concurrency control ensures that database operations can be executed concurrently without compromising correctness. - Pessimistic concurrency control, such as used in systems - with :term:`locks `, will block any potentially - conflicting operations even if they may not turn out to - actually conflict. Optimistic concurrency control, the approach - used by :ref:`WiredTiger `, will delay - checking until after a conflict may have occurred, aborting and - retrying one of the operations involved in any :term:`write - conflict` that arises. + Pessimistic concurrency control, such as that used in systems + with :term:`locks `, blocks any potentially + conflicting operations even if they may not conflict. + Optimistic concurrency control, the approach + used by :ref:`WiredTiger `, delays + checking until after a conflict may have occurred, ending and + retrying one of the operations in any :term:`write + conflict`. config database - An internal database that holds the metadata associated with a - :term:`sharded cluster`. Applications and administrators should - not modify the ``config`` database in the course of normal - operation. See :doc:`/reference/config-database`. + An internal database with metadata for a :term:`sharded cluster`. + Typically, you don't modify the ``config`` database. For more + information about the ``config`` database, see + :doc:`/reference/config-database`. config server A :binary:`~bin.mongod` instance that stores all the metadata @@ -235,7 +238,7 @@ Glossary See :ref:`sharding-config-server`. connection pool - A cache of database connections maintained by the driver. These + A cache of database connections maintained by the driver. The cached connections are re-used when connections to the database are required, instead of opening new connections. @@ -252,26 +255,25 @@ Glossary Read, Update, and Delete. See :doc:`/crud`. CSV - A text-based data format consisting of comma-separated values. - This format is commonly used to exchange data between relational - databases since the format is well-suited to tabular data. You can + A text data format with comma-separated values. + CSV files can be used to exchange data between relational + databases because CSV files have tabular data. You can import CSV files using :binary:`~bin.mongoimport`. cursor A pointer to the result set of a :term:`query`. Clients can iterate through a cursor to retrieve results. By default, cursors not opened within a session automatically timeout after 10 - minutes of inactivity. Cursors opened under a session close with + minutes of inactivity. Cursors opened in a session close with the end or timeout of the session. See :ref:`read-operations-cursors`. daemon - The conventional name for a background, non-interactive - process. + A background, non-interactive process. data directory - The file-system location where the :binary:`~bin.mongod` stores data - files. The :setting:`~storage.dbPath` option specifies the data directory. + The file system location where :binary:`~bin.mongod` stores data + files. :setting:`~storage.dbPath` specifies the data directory. data files Store document data and indexes. The :setting:`~storage.dbPath` @@ -289,9 +291,9 @@ Glossary :doc:`/data-center-awareness`. database - A physical container for :term:`collections `. - Each database gets its own set of files on the file - system. A single MongoDB server typically has multiple + A container for :term:`collections `. + Each database has a set of files in the file + system. One MongoDB server typically has multiple databases. database command @@ -317,7 +319,7 @@ Glossary delayed member A :term:`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 + protecting data from human error (unintentionally deleted databases) or updates that have unforeseen effects on the production database. See :ref:`replica-set-delayed-members`. @@ -340,21 +342,20 @@ Glossary driver A client library for interacting with MongoDB in a particular - language. See :driver:`driver `. + computer language. See :driver:`driver `. 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 :binary:`~bin.mongod` server, a write operation is - considered durable when it has been written to the server's - :term:`journal` file. For a :doc:`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. + A write operation is durable when it persists after a shutdown (or + crash) and restart of one or more server processes. For a single + :binary:`~bin.mongod` server, a write operation is considered + durable when it has been written to the server's :term:`journal` + file. For a :doc:`replica set `, a write operation + is considered durable after the write operation achieves + durability on a majority of voting nodes and written to a majority + of voting nodes' journals. election - The process by which members of a :term:`replica set` select a + The process where members of a :term:`replica set` select a :term:`primary` on startup and in the event of a failure. See :ref:`replica-set-elections`. @@ -365,11 +366,11 @@ Glossary 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. + that readable members aren't required to have the latest + updates. expression - In the context of an :term:`aggregation pipeline`, expressions are + In an :term:`aggregation pipeline`, expressions are the stateless transformations that operate on the data that passes through a :term:`pipeline`. See :doc:`/core/aggregation-pipeline`. @@ -384,19 +385,21 @@ Glossary databases. See :ref:`document-structure`. field path - Path to a field in the document. To specify a field path, use a + Path to a field in a document. To specify a field path, use a string that prefixes the field name with a dollar sign (``$``). firewall - A system level networking filter that restricts access based on, - among other things, IP address. Firewalls form a part of an - effective network security strategy. See - :ref:`security-firewalls`. + A system level network filter that restricts access based on + IP addresses and other parameters. Firewalls are part of a + secure network. See :ref:`security-firewalls`. fsync - A system call that flushes all dirty, in-memory pages to - disk. MongoDB calls ``fsync()`` on its database files at least - every 60 seconds. See :dbcommand:`fsync`. + A system call that flushes all dirty, in-memory pages to storage. + As applications write data, MongoDB records the data in the + storage layer and then writes the data to disk within the + ``syncPeriodSecs`` interval, which is 60 seconds by default. Run + ``fsync`` if you want to flush writes to disk ahead of that + interval. For details, see :dbcommand:`fsync`. geohash A geohash value is a binary representation of the location on a @@ -415,11 +418,11 @@ Glossary GridFS A convention for storing large files in a MongoDB database. All of - the official MongoDB drivers support this convention, as does the + the official MongoDB drivers support the GridFS convention, as does the :binary:`~bin.mongofiles` program. See :doc:`/core/gridfs`. hashed shard key - A special type of :term:`shard key` that uses a hash of the value + A type of :term:`shard key` that uses a hash of the value in the shard key field to distribute documents among members of the :term:`sharded cluster`. See :ref:`index-type-hashed`. @@ -431,14 +434,14 @@ Glossary health manager A health manager runs health checks on a :term:`health manager facet` at a specified :ref:`intensity level - `. Health manager checks run at + `. The health manager checks are run at specified time intervals. A health manager can be configured to move a failing :ref:`mongos ` out of a cluster - automatically. + automatically. health manager facet - A specific set of features and functionality that a :term:`health - manager` can be configured to run health checks against. For + A set of features that a :term:`health + manager` can be configured to run health checks for. For example, you can configure a health manager to monitor and manage DNS or LDAP cluster health issues automatically. See :ref:`health-managers-facets` for details. @@ -450,28 +453,28 @@ Glossary 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. MongoDB + redundancy, and automatic failover. Applications + supported by the system can operate without + downtime for a long time period. MongoDB :ref:`replica sets ` support - high availability when deployed according to our documented + high availability when deployed according to the :ref:`best practices `. For guidance on replica set deployment architecture, see :ref:`replica-set-architecture`. idempotent - The quality of an operation to produce the same result given the - same input, whether run once or run multiple times. + An operation produces the same result with the + same input when run multiple times. index A data structure that optimizes queries. See :doc:`/indexes`. init script - A simple shell script used by a Linux platform's + A shell script used by a Linux platform's :term:`init system` to start, restart, or stop a :term:`daemon` - process. If you installed MongoDB via a package manager, an init - script has been provided for your system as part of the + process. If you installed MongoDB using a package manager, an init + script is provided for your system as part of the installation. See the respective :doc:`Installation Guide ` for your operating system. @@ -494,38 +497,36 @@ Glossary :ref:`replica-set-initial-sync`. intent lock - A :term:`lock` on a resource that indicates that the holder - of the lock will read (intent shared) or write (intent + A :term:`lock` on a resource that indicates the lock holder + will read from (intent shared) or write to (intent exclusive) the resource using :term:`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 :ref:`faq-concurrency-locking`. + resource. See :ref:`faq-concurrency-locking`. 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. + A revision to the IP (Internet Protocol) standard with a + large address space to support Internet hosts. ISODate The international date format used by :binary:`~bin.mongosh` - to display dates. The format is: ``YYYY-MM-DD HH:MM.SS.millis``. + to display dates. The format is ``YYYY-MM-DD HH:MM.SS.millis``. indexed sort - A sort in which an index provides the sorted result. Sort operations that + A sort where an index provides the sorted result. Sort operations that use an index often have better performance than a :term:`blocking sort`. See :ref:`Use Indexed to Sort Query Results ` for more information. interrupt point - A point in an operation's lifecycle when it can - safely abort. MongoDB only terminates an operation + A point in an operation when it can + safely end. MongoDB only ends an operation at designated interrupt points. See :doc:`/tutorial/terminate-running-operations`. JavaScript - A popular scripting language originally designed for web - browsers. :mongosh:`mongosh `, the legacy - :binary:`mongo ` shell, and certain server-side + A scripting language. :mongosh:`mongosh `, the legacy + :binary:`mongo ` shell, and certain server functions use a JavaScript interpreter. See :doc:`/core/server-side-javascript` for more information. @@ -539,7 +540,7 @@ Glossary See :doc:`/core/journaling/`. JSON - JavaScript Object Notation. A human-readable, plain text format + JavaScript Object Notation. A plain text format for expressing structured data with support in many programming languages. For more information, see ``_. Certain MongoDB tools render an approximation of MongoDB @@ -552,21 +553,21 @@ Glossary ``_. JSONP - :term:`JSON` with Padding. Refers to a method of injecting JSON + :term:`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. + An authorization policy that grants a user only the access + that is essential to that user's work. legacy coordinate pairs - The format used for :term:`geospatial` data prior to MongoDB + The format used for :term:`geospatial` data before MongoDB version 2.4. This format stores geospatial data as points on a - planar coordinate system (e.g. ``[ x, y ]``). See + planar coordinate system (for example, ``[ x, y ]``). See :doc:`/geospatial-queries`. LineString - A LineString is defined by an array of two or more positions. A + A LineString is 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: ``_. To use a @@ -575,11 +576,16 @@ Glossary lock MongoDB uses locks to ensure that :doc:`concurrency ` - does not affect correctness. MongoDB uses :term:`read locks + does not affect correctness. MongoDB uses :term:`read locks `, :term:`write locks ` and :term:`intent locks `. For more information, see :ref:`faq-concurrency-locking`. + log files + Contain server events, such as incoming connections, commands run, + and issues encountered. For more details, see + :ref:`log-messages-ref`. + LVM Logical volume manager. LVM is a program that abstracts disk images from physical devices and provides a number of raw disk @@ -588,26 +594,29 @@ Glossary :ref:`lvm-backup-and-restore`. 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). + A structure in programming languages that associate keys with + values. Keys may contain embedded pairs of keys and values + (for example, dictionaries, hashes, maps, and associative arrays). The properties of these structures depend on the language - specification and implementation. Generally the order of keys in + specification and implementation. Typically, the order of keys in mapping types is arbitrary and not guaranteed. map-reduce - A data processing and aggregation paradigm consisting of a "map" - phase that selects data and a "reduce" phase that transforms the + An aggregation process that has a "map" + phase that selects the 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 + using map-reduce. For the map-reduce implementation, see :doc:`/core/map-reduce`. For all approaches to aggregation, see :doc:`/aggregation`. md5 - A hashing algorithm used to efficiently provide - reproducible unique strings to identify and :term:`checksum` - data. MongoDB uses md5 to identify chunks of data for - :term:`GridFS`. See :doc:`/reference/command/filemd5`. + A hashing algorithm that calculates a :term:`checksum` for the + supplied data. The algorithm returns a unique value + to identify the data. MongoDB uses md5 to identify chunks of data + for :term:`GridFS`. See :doc:`/reference/command/filemd5`. + + mean + Average of a set of numbers. member An individual :term:`mongod` process. A :term:`replica set` has @@ -625,6 +634,9 @@ Glossary :binary:`~bin.mongofiles` tool provides an option to specify a MIME type to describe a file inserted into :term:`GridFS` storage. + mode + Number that occurs most frequently in a set of numbers. + mongo The legacy MongoDB shell. The :binary:`~bin.mongo` process starts the legacy shell as a :term:`daemon` connected to either a @@ -638,15 +650,15 @@ Glossary mongod The MongoDB database server. The :binary:`~bin.mongod` process starts the MongoDB server as a :term:`daemon`. The MongoDB server - manages data requests and formats and manages background - operations. See :doc:`/reference/program/mongod`. + manages data requests and background operations. See + :doc:`/reference/program/mongod`. mongos The MongoDB sharded cluster query router. The :binary:`~bin.mongos` process starts the MongoDB router as a :term:`daemon`. The MongoDB router acts as an interface between an application and a MongoDB :term:`sharded cluster` and - handles all routing and load balancing across the cluster. See + handles all routing and load balancing across the cluster. See :doc:`/reference/program/mongos`. mongosh @@ -658,14 +670,13 @@ Glossary :binary:`~bin.mongo` as the preferred shell. 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 + A namespace is a combination of the database name and + the name of the collection or index: + ``.``. All documents belong to a namespace. See :ref:`faq-dev-namespace`. natural order - The order in which the database refers to documents on disk. This is the + The order that the database stores documents on disk. Natural order is the default sort order. See :operator:`$natural` and :ref:`return-natural-order`. @@ -674,14 +685,16 @@ Glossary 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 + Sometimes, partitions are partial or asymmetric. An example + partial partition is the 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 + communicate with members of the second set, and the reverse, 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 + the partition can communicate with the other side only if they originate the communications channel. node @@ -697,9 +710,9 @@ Glossary See :term:`natural order`. ObjectId - A special 12-byte :term:`BSON` type that guarantees uniqueness - within the :term:`collection`. The ObjectId is generated based on - timestamp, machine ID, process ID, and a process-local incremental + A 12-byte :term:`BSON` type that is unique + within a :term:`collection`. The ObjectId is generated using the + timestamp, computer ID, process ID, and a local process incremental counter. MongoDB uses ObjectId values as the default values for :term:`_id` fields. @@ -725,10 +738,10 @@ Glossary See :doc:`/core/replica-set-oplog`. oplog hole - A temporary gap in the oplog due to oplog writes not occurring in + A temporary gap in the oplog because the oplog writes aren't in sequence. Replica set :ref:`primaries ` apply oplog entries in parallel as a batch operation. As a result, - temporary gaps in the oplog can occur from entries that are not + temporary gaps in the oplog can occur from entries that aren't yet written from a batch. oplog window @@ -753,9 +766,9 @@ Glossary 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. + shard that also exist in chunks on other shards. This is caused by + a failed migration or an incomplete migration cleanup because of + an atypical shutdown. Starting in MongoDB 4.4, orphaned documents are cleaned up automatically after a chunk migration completes. You no longer @@ -763,7 +776,7 @@ Glossary documents. orphaned cursor - A cursor that is not properly closed or iterated over + A cursor that is not correctly closed or iterated over in your application code. Orphaned cursors can cause performance issues in your MongoDB deployment. @@ -834,13 +847,13 @@ Glossary :ref:`replica-set-primary-member`. primary key - A record's unique immutable identifier. In an :term:`RDBMS`, the primary + A record's unique immutable identifier. In :term:`RDBMS` software, the primary key is typically an integer stored in each row's ``id`` field. - In MongoDB, the :term:`_id` field holds a document's primary - key which is usually a BSON :term:`ObjectId`. + In MongoDB, the :term:`_id` field stores a document's primary + key, which is typically a BSON :term:`ObjectId`. primary shard - The :term:`shard` that holds all the un-sharded collections. See + The :term:`shard` that stores all the unsharded collections. See :ref:`primary-shard`. priority @@ -854,16 +867,16 @@ Glossary :ref:`privilege `. projection - A document given to a :term:`query` that specifies which fields - MongoDB returns in the result set. See :ref:`projection`. For a - list of projection operators, see + A document supplied to a :term:`query` that specifies the fields + MongoDB returns in the result set. For more information about projections, + see :ref:`projection` and :doc:`/reference/operator/projection`. query - A read request. MongoDB uses a :term:`JSON`-like query language - that includes a variety of :term:`query operators ` with + A read request. MongoDB uses a :term:`JSON` form of query language + that includes :term:`query operators ` with names that begin with a ``$`` character. In - :binary:`~bin.mongosh`, you can issue queries using the + :binary:`~bin.mongosh`, you can run queries using the :method:`db.collection.find()` and :method:`db.collection.findOne()` methods. See :ref:`read-operations-queries`. @@ -876,19 +889,23 @@ Glossary query optimizer A process that generates query plans. For each query, the optimizer generates a plan that matches the query to the index - that will return results as efficiently as possible. The + that returns the results as efficiently as possible. The optimizer reuses the query plan each time the query runs. If a collection changes significantly, the optimizer creates a new query plan. See :ref:`read-operations-query-optimization`. + query plan + Most efficient execution plan chosen by the query planner. For + more details, see :ref:`query-plans-query-optimization`. + query shape A combination of query predicate, sort, projection, and :doc:`collation `. The query shape allows MongoDB to identify logically equivalent queries and analyze their performance. For the query predicate, only the structure of the predicate, - including the field names, are significant; the values in the - query predicate are insignificant. As such, a query predicate ``{ + including the field names, are significant. The values in the + query predicate are insignificant. Therefore, a query predicate ``{ type: 'food' }`` is equivalent to the query predicate ``{ type: 'utensil' }`` for a query shape. @@ -915,19 +932,14 @@ Glossary RDBMS Relational Database Management System. A database management - system based on the relational model, typically using - :term:`SQL` as the query language. + system based on the relational model, typically using :term:`SQL` + as the query language. recovering A :term:`replica set` member status indicating that a member - is not ready to begin normal activities of a secondary or primary. + is not ready to begin activities of a secondary or primary. Recovering members are unavailable for reads. - replica pairs - The precursor to the MongoDB :term:`replica sets `. - - .. deprecated:: 1.6 - replica set A cluster of MongoDB servers that implements replication and automated failover. MongoDB's recommended @@ -935,20 +947,20 @@ Glossary replication A feature allowing multiple database servers to share the same - data, thereby ensuring redundancy and facilitating load balancing. - See :doc:`/replication`. + data. Replication ensures data redundancy and enables load + balancing. See :doc:`/replication`. replication lag - The length of time between the last operation in the + The time period between the last operation in the :term:`primary's ` :term:`oplog` and the last operation - applied to a particular :term:`secondary`. In general, you want to - keep replication lag as small as possible. See :ref:`Replication + applied to a particular :term:`secondary`. You typically want + replication lag as short as possible. See :ref:`Replication Lag `. resident memory The subset of an application's memory currently stored in physical RAM. Resident memory is a subset of :term:`virtual memory`, - which includes memory mapped to physical RAM and to disk. + which includes memory mapped to physical RAM and to storage. resource A database, collection, set of collections, or cluster. A @@ -962,19 +974,19 @@ Glossary :doc:`/security`. rollback - A process that reverts writes operations to ensure the consistency + A process that reverts write operations to ensure the consistency of all replica set members. See :ref:`replica-set-rollback`. secondary A :term:`replica set` member that replicates the contents of the - master database. Secondary members may handle read requests, but - only the :term:`primary` members can handle write operations. See + master database. Secondary members may run read requests, but + only the :term:`primary` members can run write operations. See :ref:`replica-set-secondary-members`. secondary index A database :term:`index` that improves query performance by minimizing the amount of work that the query engine must perform - to fulfill a query. See :doc:`/indexes`. + to run a query. See :doc:`/indexes`. secondary member See :term:`secondary`. Also known as a secondary node. @@ -984,7 +996,7 @@ Glossary :binary:`~bin.mongosh`) for initial discovery of the replica set configuration. Seed lists can be provided as a list of ``host:port`` pairs (see :ref:`connections-standard-connection-string-format` - or via DNS entries (see :ref:`connections-dns-seedlist`). + or through DNS entries. For more information, see :ref:`connections-dns-seedlist`. set name The arbitrary name given to a replica set. All members of a @@ -992,10 +1004,11 @@ Glossary :setting:`~replication.replSetName` setting or the :option:`--replSet ` option. shard - A single :binary:`~bin.mongod` instance or :term:`replica set` that - stores some portion of a :term:`sharded cluster's ` total data set. In production, all shards should be - replica sets. See :doc:`/core/sharded-cluster-shards`. + A single :binary:`~bin.mongod` instance or :term:`replica set` + that stores part of a :term:`sharded cluster's ` + total data set. Typically, in a production deployment, ensure all + shards are part of replica sets. See + :doc:`/core/sharded-cluster-shards`. shard key The field MongoDB uses to distribute documents among members of a @@ -1013,22 +1026,22 @@ Glossary Sharding enables horizontal scaling. See :doc:`/sharding`. shell helper - A method in ``mongosh`` that provides a more concise + A method in ``mongosh`` that has a concise syntax for a :doc:`database command `. Shell helpers - improve the general interactive experience. See + improve the interactive experience. See :doc:`/reference/method`. single-master replication A :term:`replication` topology where only a single database instance accepts writes. Single-master replication ensures - consistency and is the replication topology employed by MongoDB. + consistency and is the replication topology used by MongoDB. See :doc:`/core/replica-set-primary`. snapshot .. include:: /includes/snapshot-definition.rst snappy - A compression/decompression library designed to balance + A compression/decompression library to balance efficient computation requirements with reasonable compression rates. Snappy is the default compression library for MongoDB's use of :ref:`WiredTiger @@ -1042,26 +1055,18 @@ Glossary cluster`. See :doc:`/core/sharding-data-partitioning`. 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. 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. Complex - SQL is generally not directly portable between major - :term:`RDBMS` products. ``SQL`` is often used as - metonym for relational databases. + Structured Query Language (SQL) is used for interaction with + relational databases. SSD - Solid State Disk. 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. + Solid State Disk. High-performance storage that uses solid + state electronics for persistence instead of rotating platters + and movable read/write heads used by mechanical hard drives. standalone - An instance of :binary:`~bin.mongod` that is running as a single - server and not as part of a :term:`replica set`. To convert a - standalone into a replica set, see + An instance of :binary:`~bin.mongod` that runs as a single server + and not as part of a :term:`replica set`. To convert it to a + replica set, see :doc:`/tutorial/convert-standalone-to-replica-set`. storage engine @@ -1073,7 +1078,7 @@ Glossary strict consistency A property of a distributed system requiring that all members - always reflect the latest changes to the system. In a database + contain the latest changes to the system. In a database system, this means that any system that can provide data must reflect the latest writes at all times. @@ -1099,13 +1104,10 @@ Glossary tag A label applied to a replica set member and used by clients to issue data-center-aware operations. For more information - on using tags with replica sets, see the following - sections of this manual: :ref:`replica-set-read-preference-tag-sets`. - - .. versionchanged:: 3.4 + on using tags with replica sets, see :ref:`replica-set-read-preference-tag-sets`. - In MongoDB 3.4, sharded cluster :term:`zones ` replace - :term:`tags `. + In MongoDB 3.4, sharded cluster :term:`zones ` replace + :term:`tags `. tag set A document containing zero or more :term:`tags `. @@ -1126,11 +1128,12 @@ Glossary :doc:`/core/timeseries-collections`. 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. :term:`primary`, :term:`secondary`, - :term:`config server`, or :binary:`~bin.mongos`.) + The state of a deployment of MongoDB instances. Includes: + + - Type of deployment (standalone, replica set, or sharded cluster). + - Availability of servers. + - Role of each server (:term:`primary`, :term:`secondary`, + :term:`config server`, or :binary:`~bin.mongos`). transaction Group of read or write operations. For details, see @@ -1146,18 +1149,18 @@ Glossary TSV A text-based data format consisting of tab-separated values. This format is commonly used to exchange data between relational - databases, since the format is well-suited to tabular data. You can + databases because the format is suited to tabular data. You can import TSV files using :binary:`~bin.mongoimport`. TTL - Stands for "time to live" and represents an expiration time or + Time-to-live (TTL) is 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. MongoDB has a TTL collection feature. See :doc:`/tutorial/expire-data`. unique index - An index that enforces uniqueness for a particular field across + An index that enforces uniqueness for a particular field in a single collection. See :ref:`index-type-unique`. unordered query plan @@ -1166,13 +1169,16 @@ Glossary See :ref:`read-operations-query-optimization`. upsert - An option for update operations; e.g. + An option for update operations. For example: :method:`db.collection.updateOne()`, - :method:`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 :ref:`upsert-parameter`. + :method:`db.collection.findAndModify()`. If upsert is ``true``, + the update operation either: + + - updates the document(s) matched by the query. + - or if no documents match, inserts a new document. The new + document has the field values specified in the update operation. + + For more information about upserts, see :ref:`upsert-parameter`. virtual memory An application's working memory, typically residing on both @@ -1200,11 +1206,11 @@ Glossary specified number of members. See :doc:`/reference/write-concern`. 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 :term:`concurrency control`. MongoDB will - transparently abort and retry one of the conflicting operations. + A situation where two concurrent operations, at least one of which + is a write, try to use a resource that violates the + constraints for a storage engine that uses optimistic + :term:`concurrency control`. MongoDB automatically ends and + retries one of the conflicting write operations. write lock An exclusive :term:`lock` on a resource such as a collection @@ -1214,9 +1220,9 @@ Glossary locks, see :doc:`/faq/concurrency`. writeBacks - The process within the sharding system that ensures that writes - issued to a :term:`shard` that *is not* responsible for the - relevant chunk get applied to the proper shard. For related + The process in the sharding system that ensures writes + sent to a :term:`shard` that *is not* responsible for the + relevant chunk are applied to the correct shard. For more information, see :ref:`faq-writebacklisten` and :ref:`server-status-writebacksqueued`.