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MongoDB Documentation
Release 2.4.8
MongoDB Documentation Project
November 26,2013
2
Contents
1 Install MongoDB 3
1.1 Installation Guides............................................3
1.2 First Steps with MongoDB........................................19
2 MongoDB CRUD Operations 27
2.1 MongoDB CRUD Introduction.....................................27
2.2 MongoDB CRUD Concepts.......................................29
2.3 MongoDB CRUD Tutorials.......................................58
2.4 MongoDB CRUD Reference.......................................82
3 Data Models 97
3.1 Data Modeling Introduction.......................................97
3.2 Data Modeling Concepts.........................................99
3.3 Data Model Examples and Patterns...................................106
3.4 Data Model Reference..........................................121
4 Administration 135
4.1 Administration Concepts.........................................135
4.2 Administration Tutorials.........................................169
4.3 Administration Reference........................................224
5 Security 237
5.1 Security Introduction...........................................237
5.2 Security Concepts............................................239
5.3 Security Tutorials.............................................245
5.4 Security Reference............................................267
6 Aggregation 277
6.1 Aggregation Introduction........................................277
6.2 Aggregation Concepts..........................................281
6.3 Aggregation Examples..........................................292
6.4 Aggregation Reference..........................................308
7 Indexes 313
7.1 Index Introduction............................................313
7.2 Index Concepts..............................................318
7.3 Indexing Tutorials............................................338
7.4 Indexing Reference............................................374
1
8 Replication 377
8.1 Replication Introduction.........................................377
8.2 Replication Concepts...........................................381
8.3 Replica Set Tutorials...........................................419
8.4 Replication Reference..........................................466
9 Sharding 491
9.1 Sharding Introduction..........................................491
9.2 Sharding Concepts............................................496
9.3 Sharded Cluster Tutorials........................................517
9.4 Sharding Reference...........................................558
10 Frequently Asked Questions 575
10.1 FAQ:MongoDB Fundamentals.....................................575
10.2 FAQ:MongoDB for Application Developers..............................578
10.3 FAQ:The mongo Shell.........................................588
10.4 FAQ:Concurrency............................................590
10.5 FAQ:Sharding with MongoDB.....................................594
10.6 FAQ:Replica Sets and Replication in MongoDB............................600
10.7 FAQ:MongoDB Storage.........................................603
10.8 FAQ:Indexes...............................................607
10.9 FAQ:MongoDB Diagnostics.......................................610
11 Release Notes 615
11.1 Current Stable Release..........................................615
11.2 Previous Stable Releases.........................................633
11.3 Other MongoDB Release Notes.....................................658
11.4 MongoDB Version Numbers.......................................659
12 About MongoDB Documentation 661
12.1 License..................................................661
12.2 Editions..................................................661
12.3 Version and Revisions..........................................662
12.4 Report an Issue or Make a Change Request...............................662
12.5 Contribute to the Documentation....................................662
Index 679
2
MongoDB Documentation,Release 2.4.8
See About MongoDB Documentation (page 661) for more information about the MongoDB Documentation project,
this Manual and additional editions of this text.
Note:This version of the PDF does not include the reference section,see MongoDB Reference Manual
1
for a PDF
edition of all MongoDB Reference Material.
1
http://docs.mongodb.org/v2.4/MongoDB-reference-manual.pdf
Contents 1
MongoDB Documentation,Release 2.4.8
2 Contents
CHAPTER 1
Install MongoDB
MongoDB runs on most platforms and supports both 32-bit and 64-bit architectures.
1.1 Installation Guides
See
Release Notes (page 615) for information about specific releases of MongoDB.
1.1.1 Linux
Install on Linux (page 3)
Install on Linux
These documents provide instructions to install MongoDB for various Linux systems.
Recommended
For easy installation,MongoDB provides packages for popular Linux distributions.The following guides detail the
installation process for these systems:
Install on Red Hat Enterprise Linux (page 4) Install MongoDB on Red Hat Enterprise,CentOS,Fedora and related
Linux systems using.rpm packages.
Install on Ubuntu (page 6) Install MongoDB on Ubuntu Linux systems using.deb packages.
Install on Debian (page 7) Install MongoDB on Debian systems using.deb packages.
For systems without supported packages,refer to the Manual Installation tutorial.
Manual Installation
Although packages are the preferred installation method,for Linux systems without supported packages,see the
following guide:
Install on Other Linux Systems (page 9) Install MongoDB on other Linux systems fromthe MongoDB archives.
3
MongoDB Documentation,Release 2.4.8
Install MongoDB on Red Hat Enterprise,CentOS,or Fedora This tutorial outlines the steps to install MongoDB
on Red Hat Enterprise Linux,CentOS Linux,Fedora Linux and related systems.The tutorial uses.rpm packages to
install.While some of these distributions include their own MongoDB packages,the official MongoDB packages are
generally more up to date.
Packages The MongoDB downloads repository contains two packages:
• mongo-10gen-server
This package contains the mongod and mongos daemons from the latest stable release and associated con-
figuration and init scripts.Additionally,you can use this package to install daemons from a previous release
(page 4) of MongoDB.
• mongo-10gen
This package contains all MongoDB tools fromthe latest stable release.Additionally,you can use this package
to install tools from a previous release (page 4) of MongoDB.Install this package on all production MongoDB
hosts and optionally on other systems fromwhich you may need to administer MongoDB systems.
Install MongoDB
Configure Package Management System(YUM) Create a/etc/yum.repos.d/mongodb.repo file to hold
the following configuration information for the MongoDB repository:
Tip
For production deployments,always run MongoDB on 64-bit systems.
If you are running a 64-bit system,use the following configuration:
[mongodb]
name=MongoDB Repository
baseurl=http://downloads-distro.mongodb.org/repo/redhat/os/x86_64/
gpgcheck=0
enabled=1
If you are running a 32-bit system,which is not recommended for production deployments,use the following config-
uration:
[mongodb]
name=MongoDB Repository
baseurl=http://downloads-distro.mongodb.org/repo/redhat/os/i686/
gpgcheck=0
enabled=1
Install Packages Issue the following command (as root or with sudo) to install the latest stable version of Mon-
goDB and the associated tools:
yum install mongo-10gen mongo-10gen-server
When this command completes,you have successfully installed MongoDB!
Manage Installed Versions You can use the mongo-10gen and mongo-10gen-server packages to install
previous releases of MongoDB.To install a specific release,append the version number,as in the following example:
4 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
yum install mongo-10gen-2.2.3 mongo-10gen-server-2.2.3
This installs the mongo-10gen and mongo-10gen-server packages with the 2.2.3 release.You can specify
any available version of MongoDB;however yum will upgrade the mongo-10gen and mongo-10gen-server
packages when a newer version becomes available.Use the following pinning procedure to prevent unintended up-
grades.
To pin a package,add the following line to your/etc/yum.conf file:
exclude=mongo-10gen,mongo-10gen-server
Control Scripts
Warning:With the introduction of systemd in Fedora 15,the control scripts included in the packages available
in the MongoDB downloads repository are not compatible with Fedora systems.A correction is forthcoming,
see SERVER-7285
a
for more information,and in the mean time use your own control scripts or install using the
procedure outlined in Install MongoDB on Linux Systems (page 9).
a
https://jira.mongodb.org/browse/SERVER-7285
The packages include various control scripts,including the init script/etc/rc.d/init.d/mongod.These pack-
ages configure MongoDB using the/etc/mongod.conf file in conjunction with the control scripts.
As of version 2.4.8,there are no control scripts for mongos.mongos is only used in sharding deployments
(page 496).You can use the mongod init script to derive your own mongos control script.
Run MongoDB
Important:You must SELinux to allow MongoDB to start on Fedora systems.Administrators have two options:
• enable access to the relevant ports (e.g.27017) for SELinux.See Configuration Options (page 242) for more
information on MongoDB’s default ports (page 275).
• disable SELinux entirely.This requires a systemreboot and may have larger implications for your deployment.
Start MongoDB The MongoDB instance stores its data files in the/var/lib/mongo and its log files in
/var/log/mongo,and run using the mongod user account.If you change the user that runs the MongoDBprocess,
you must modify the access control rights to the/var/lib/mongo and/var/log/mongo directories.
Start the mongod process by issuing the following command (as root or with sudo):
service mongod start
You can verify that the mongod process has started successfully by checking the contents of the log file at
/var/log/mongo/mongod.log.
You may optionally ensure that MongoDB will start following a system reboot by issuing the following command
(with root privileges:)
chkconfig mongod on
Stop MongoDB Stop the mongod process by issuing the following command (as root or with sudo):
service mongod stop
1.1.Installation Guides 5
MongoDB Documentation,Release 2.4.8
Restart MongoDB You can restart the mongod process by issuing the following command (as root or with sudo):
service mongod restart
Follow the state of this process by watching the output in the/var/log/mongo/mongod.log file to watch for
errors or important messages fromthe server.
Install MongoDB on Ubuntu This tutorial outlines the steps to install MongoDB on Ubuntu Linux systems.The
tutorial uses.deb packages to install.Although Ubuntu include its own MongoDB packages,the official MongoDB
packages are generally more up to date.
Note:If you use an older Ubuntu that does not use Upstart,(i.e.any version before 9.10 “Karmic”) please followthe
instructions on the Install MongoDB on Debian (page 7) tutorial.
Package Options The MongoDB downloads repository provides the mongodb-10gen package,which contains
the latest stable release.Additionally you can install previous releases (page 6) of MongoDB.
You cannot install this package concurrently with the mongodb,mongodb-server,or mongodb-clientspack-
ages provided by Ubuntu.
Install MongoDB
Configure Package Management System (APT) The Ubuntu package management tool (i.e.dpkg and apt)
ensure package consistency and authenticity by requiring that distributors sign packages with GPG keys.Issue the
following command to import the MongoDB public GPG Key
1
:
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 7F0CEB10
Create a/etc/apt/sources.list.d/mongodb.list file using the following command.
echo'deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen'| sudo tee/etc/apt/sources.list.d/mongodb.list
Now issue the following command to reload your repository:
sudo apt-get update
Install Packages Issue the following command to install the latest stable version of MongoDB:
sudo apt-get install mongodb-10gen
When this command completes,you have successfully installed MongoDB!Continue for configuration and start-up
suggestions.
Manage Installed Versions You can use the mongodb-10gen package to install previous versions of MongoDB.
To install a specific release,append the version number to the package name,as in the following example:
apt-get install mongodb-10gen=2.2.3
This will install the 2.2.3 release of MongoDB.You can specify any available version of MongoDB;however
apt-get will upgrade the mongodb-10gen package when a newer version becomes available.Use the following
pinning procedure to prevent unintended upgrades.
1
http://docs.mongodb.org/10gen-gpg-key.asc
6 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
To pin a package,issue the following command at the system prompt to pin the version of MongoDB at the currently
installed version:
echo"mongodb-10gen hold"| sudo dpkg --set-selections
Control Scripts The packages include various control scripts,including the init script
/etc/rc.d/init.d/mongod.These packages configure MongoDB using the/etc/mongod.conf file
in conjunction with the control scripts.
As of version 2.4.8,there are no control scripts for mongos.mongos is only used in sharding deployments
(page 496).You can use the mongod init script to derive your own mongos control script.
Run MongoDB The MongoDB instance stores its data files in the/var/lib/mongo and its log files in
/var/log/mongo,and run using the mongod user account.If you change the user that runs the MongoDBprocess,
you must modify the access control rights to the/var/lib/mongo and/var/log/mongo directories.
Start MongoDB You can start the mongod process by issuing the following command:
sudo service mongodb start
You can verify that mongod has started successfully by checking the contents of the log file at
/var/log/mongodb/mongodb.log.
Stop MongoDB As needed,you may stop the mongod process by issuing the following command:
sudo service mongodb stop
Restart MongoDB You may restart the mongod process by issuing the following command:
sudo service mongodb restart
Install MongoDB on Debian This tutorial outlines the steps to install MongoDB on Debian systems.The tutorial
uses.deb packages to install.While some Debian distributions include their own MongoDB packages,the official
MongoDB packages are generally more up to date.
Note:This tutorial applies to both Debian systems and versions of Ubuntu Linux prior to 9.10 “Karmic” which do
not use Upstart.Other Ubuntu users will want to follow the Install MongoDB on Ubuntu (page 6) tutorial.
Package Options The downloads repository provides the mongodb-10gen package,which contains the latest
stable release.Additionally you can install previous releases (page 8) of MongoDB.
You cannot install this package concurrently with the mongodb,mongodb-server,or mongodb-clientspack-
ages that your release of Debian may include.
Install MongoDB
Configure Package Management System (APT) The Debian package management tools (i.e.dpkg and apt)
ensure package consistency and authenticity by requiring that distributors sign packages with GPG keys.
1.1.Installation Guides 7
MongoDB Documentation,Release 2.4.8
Step 1:Import MongoDB PGP Key Issue the following command to add the MongoDB public GPG Key
2
to the
systemkey ring.
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10
Step 2:Create a sources.listfile for MongoDB Create a/etc/apt/sources.list.d/mongodb.list
file
echo'deb http://downloads-distro.mongodb.org/repo/debian-sysvinit dist 10gen'| sudo tee/etc/apt/sources.list.d/mongodb.list
Step 3:Reload Local Package Database Issue the following command to reload the local package database:
sudo apt-get update
Install Packages Issue the following command to install the latest stable version of MongoDB:
sudo apt-get install mongodb-10gen
When this command completes,you have successfully installed MongoDB!
Manage Installed Versions You can use the mongodb-10gen package to install previous versions of MongoDB.
To install a specific release,append the version number to the package name,as in the following example:
apt-get install mongodb-10gen=2.2.3
This will install the 2.2.3 release of MongoDB.You can specify any available version of MongoDB;however
apt-get will upgrade the mongodb-10gen package when a newer version becomes available.Use the following
pinning procedure to prevent unintended upgrades.
To pin a package,issue the following command at the system prompt to pin the version of MongoDB at the currently
installed version:
echo"mongodb-10gen hold"| sudo dpkg --set-selections
Control Scripts The packages include various control scripts,including the init script
/etc/rc.d/init.d/mongod.These packages configure MongoDB using the/etc/mongod.conf file
in conjunction with the control scripts.
As of version 2.4.8,there are no control scripts for mongos.mongos is only used in sharding deployments
(page 496).You can use the mongod init script to derive your own mongos control script.
Run MongoDB The MongoDB instance stores its data files in the/var/lib/mongo and its log files in
/var/log/mongo,and run using the mongod user account.If you change the user that runs the MongoDBprocess,
you must modify the access control rights to the/var/lib/mongo and/var/log/mongo directories.
Start MongoDB Issue the following command to start mongod:
sudo/etc/init.d/mongodb start
You can verify that mongod has started successfully by checking the contents of the log file at
/var/log/mongodb/mongodb.log.
2
http://docs.mongodb.org/10gen-gpg-key.asc
8 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
Stop MongoDB Issue the following command to stop mongod:
sudo/etc/init.d/mongodb stop
Restart MongoDB Issue the following command to restart mongod:
sudo/etc/init.d/mongodb restart
Install MongoDB on Linux Systems Compiled versions of MongoDB for Linux provide a simple option for in-
stalling MongoDB for other Linux systems without supported packages.
Installation Process MongoDBprovides archives for both 64-bit and 32-bit Linux.Followthe installation procedure
appropriate for your system.
Install for 64-bit Linux
Step 1:Download the Latest Release In a systemshell,download the latest release for 64-bit Linux.
curl -O http://downloads.mongodb.org/linux/mongodb-linux-x86_64-2.5.4.tgz
You may optionally specify a different version to download.
Step 2:Extract MongoDB FromArchive Extract the files fromthe downloaded archive.
tar -zxvf mongodb-linux-x86_64-2.5.4.tgz
Step 3:Optional.Copy MongoDB to Target Directory Copy the extracted folder into another location,such as
mongodb.
mkdir -p mongodb
cp -R -n mongodb-linux-x86_64-2.5.4/mongodb
Step 4:Optional.Configure Search Path To ensure that the downloaded binaries are in your PATH,you can
modify your PATH and/or create symbolic links to the MongoDB binaries in your/usr/local/bin directory
(/usr/local/bin is already in your PATH).You can find the MongoDB binaries in the bin/directory within the
archive.
Install for 32-bit Linux
Step 1:Download the Latest Release In a systemshell,download the latest release for 32-bit Linux.
curl -O http://downloads.mongodb.org/linux/mongodb-linux-i686-2.5.4.tgz
You may optionally specify a different version to download.
Step 2:Extract MongoDB FromArchive Extract the files fromthe downloaded archive.
1.1.Installation Guides 9
MongoDB Documentation,Release 2.4.8
tar -zxvf mongodb-linux-i686-2.5.4.tgz
Step 3:Optional.Copy MongoDB to Target Directory Copy the extracted folder into another location,such as
mongodb.
mkdir -p mongodb
cp -R -n mongodb-linux-i686-2.5.4/mongodb
Step 4:Optional.Configure Search Path To ensure that the downloaded binaries are in your PATH,you can
modify your PATH and/or create symbolic links to the MongoDB binaries in your/usr/local/bin directory
(/usr/local/bin is already in your PATH).You can find the MongoDB binaries in the bin/directory within the
archive.
Run MongoDB
Set Up the Data Directory Before you start mongod for the first time,you will need to create the data directory
(i.e.dbpath).By default,mongod writes data to the/data/db directory.
Step 1:Create dbpath To create the default dbpath directory,use the following command:
mkdir -p/data/db
Step 2:Set dbpath Permissions Ensure that the user that runs the mongod process has read and write permissions
to this directory.For example,if you will run the mongod process,change the owner of the/data/db directory:
chown mongodb/data/db
You must create the mongodb user separately.
You can specify an alternate path for data files using the --dbpath option to mongod.If you use an alternate
location for your data directory,ensure that this user can write to the alternate data directory.
Start MongoDB To start mongod,run the executable mongod at the systemprompt.
For example,if your PATH includes the location of the mongod binary,enter mongod at the systemprompt.
mongod
If your PATH does not include the location of the mongod binary,enter the full path to the mongod binary.
Starting mongod without any arguments starts a MongoDB instance that writes data to the/data/db directory.To
specify an alternate data directory,start mongod with the --dbpath option:
mongod --dbpath <some alternate directory>
Whether using the default/data/db or an alternate directory,ensure that the user account running mongod has read
and write permissions to the directory.
Stop MongoDB To stop the mongod instance,press Control+C in the terminal where the mongod instance is
running.
10 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
1.1.2 OS X
Install MongoDB on OS X (page 11)
Install MongoDB on OS X
PlatformSupport
Starting in version 2.4,MongoDB only supports OS X versions 10.6 (Snow Leopard) on Intel x86-64 and later.
MongoDB is available through the popular OS X package manager Homebrew
3
or through the MongoDB Download
site.
Install MongoDB with Homebrew
Homebrew
4 5
installs binary packages based on published “formulae”.The following commands will update brew to
the latest packages and install MongoDB.
In a terminal shell,use the following sequence of commands to update‘‘brew‘‘ to the latest packages and install
MongoDB:
brew update
brew install mongodb
Later,if you need to upgrade MongoDB,run the following sequence of commands to update the MongoDBinstallation
on your system:
brew update
brew upgrade mongodb
Manual Installation
Step 1:Download the Latest Release In a systemshell,download the latest release for 64-bit OS X.
curl -O http://downloads.mongodb.org/osx/mongodb-osx-x86_64-2.5.4.tgz
You may optionally specify a different version to download.
Step 2:Extract MongoDB FromArchive Extract the files fromthe downloaded archive.
tar -zxvf mongodb-osx-x86_64-2.5.4.tgz
Step 3:Optional.Copy MongoDB to Target Directory Copy the extracted folder into another location,such as
mongodb.
mkdir -p mongodb
cp -R -n mongodb-osx-x86_64-2.5.4/mongodb
3
http://mxcl.github.com/homebrew/
4
http://brew.sh/
5
Homebrew requires some initial setup and configuration.This configuration is beyond the scope of this document.
1.1.Installation Guides 11
MongoDB Documentation,Release 2.4.8
Step 4:Optional.Configure Search Path To ensure that the downloaded binaries are in your PATH,you can
modify your PATH and/or create symbolic links to the MongoDB binaries in your/usr/local/bin directory
(/usr/local/bin is already in your PATH).You can find the MongoDB binaries in the bin/directory within the
archive.
Run MongoDB
Set Up the Data Directory Before you start mongod for the first time,you will need to create the data directory.
By default,mongod writes data to the/data/db/directory.
Step 1:Create dbpath To create the default dbpath directory,use the following command:
mkdir -p/data/db
Step 2:Set dbpath Permissions Ensure that the user that runs the mongod process has read and write permissions
to this directory.For example,if you will run the mongod process,change the owner of the/data/db directory:
chown`id -u`/data/db
You must create the mongodb user separately.
You can specify an alternate path for data files using the --dbpath option to mongod.If you use an alternate
location for your data directory,ensure that the alternate directory has the appropriate permissions.
Start MongoDB To start mongod,run the executable mongod at the systemprompt.
For example,if your PATH includes the location of the mongod binary,enter mongod at the systemprompt.
mongod
If your PATH does not include the location of the mongod binary,enter the full path to the mongod binary.
The previous command starts a mongod instance that writes data to the/data/db/directory.To specify an alternate
data directory,start mongod with the --dbpath option:
mongod --dbpath <some alternate directory>
Whether using the default/data/db/or an alternate directory,ensure that the user account running mongod has
read and write permissions to the directory.
Stop MongoDB To stop the mongod instance,press Control+C in the terminal where the mongod instance is
running.
1.1.3 Windows
Install MongoDB on Windows (page 12)
Install MongoDB on Windows
PlatformSupport
Starting in version 2.2,MongoDB does not support Windows XP.Please use a more recent version of Windows to use
more recent releases of MongoDB.
12 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
Important:If you are running any edition of Windows Server 2008 R2 or Windows 7,please install a hotfix to
resolve an issue with memory mapped files on Windows
6
.
Download MongoDB for Windows
There are three builds of MongoDB for Windows:
• MongoDBfor Windows Server 2008 R2 edition (i.e.2008R2) only runs on Windows Server 2008 R2,Windows
7 64-bit,and newer versions of Windows.This build takes advantage of recent enhancements to the Windows
Platformand cannot operate on older versions of Windows.
• MongoDB for Windows 64-bit runs on any 64-bit version of Windows newer than Windows XP,including
Windows Server 2008 R2 and Windows 7 64-bit.
• MongoDB for Windows 32-bit runs on any 32-bit version of Windows newer than Windows XP.32-bit versions
of MongoDBare only intended for older systems and for use in testing and development systems.32-bit versions
of MongoDB only support databases smaller than 2GB.
Tip
To find which version of Windows you are running,enter the following command in the Command Prompt:
wmic os get osarchitecture
1.Download the latest production release of MongoDB fromthe MongoDB downloads page
7
.Ensure you down-
load the correct version of MongoDB for your Windows system.The 64-bit versions of MongoDB will not
work with 32-bit Windows.
2.Extract the downloaded archive.
(a) In Windows Explorer,find the MongoDB download file,typically in the default Downloads directory.
(b) Extract the archive to C:\by right clicking on the archive and selecting Extract All and browsing to C:\.
3.Optional.Move the MongoDB directory to another location.For example,to move the directory to
C:\mongodb directory:
(a) Go Start Menu > All Programs > Accessories.
(b) Right click Command Prompt,and select Run as Administrator fromthe popup menu.
(c) In the Command Prompt,issue the following commands:
cd\
move C:\mongodb-win32-
*
C:\mongodb
Note:MongoDB is self-contained and does not have any other system dependencies.You can run MongoDB from
any folder you choose.You may install MongoDB in any directory (e.g.D:\test\mongodb)
Run MongoDB
6
http://support.microsoft.com/kb/2731284
7
http://www.mongodb.org/downloads
1.1.Installation Guides 13
MongoDB Documentation,Release 2.4.8
Set Up the Data Directory MongoDBrequires a data folder to store its files.The default location for the MongoDB
data directory is C:\data\db.Create this folder using the Command Prompt.Go to the C:\directory and issue the
following command sequence:
md data
md data\db
You can specify an alternate path for data files using the --dbpath option to mongod.exe.
Start MongoDB To start MongoDB,execute fromthe Command Prompt:
C:\mongodb\bin\mongod.exe
This will start the main MongoDB database process.The waiting for connections message in the console
output indicates that the mongod.exe process is running successfully.
Note:Depending on the security level of your system,Windows will issue a Security Alert dialog box about blocking
“some features” of C:\\mongodb\bin\mongod.exe from communicating on networks.All users should select
Private Networks,such as my home or work network and click Allow access.For additional
information on security and MongoDB,please read the Security Concepts (page 239) page.
Warning:Do not allowmongod.exe to be accessible to public networks without running in “Secure Mode” (i.e.
auth.) MongoDB is designed to be run in “trusted environments” and the database does not enable authentication
or “Secure Mode” by default.
You may specify an alternate path for\data\db with the dbpath setting for mongod.exe,as in the following
example:
C:\mongodb\bin\mongod.exe --dbpath d:\test\mongodb\data
If your path includes spaces,enclose the entire path in double quotations,for example:
C:\mongodb\bin\mongod.exe --dbpath"d:\test\mongo db data"
Connect to MongoDB Connect to MongoDB using the mongo.exe shell.Open another Command Prompt and
issue the following command:
C:\mongodb\bin\mongo.exe
Note:Executing the command start C:\mongodb\bin\mongo.exewill automatically start the mongo.exe
shell in a separate Command Prompt window.
The mongo.exe shell will connect to mongod.exe running on the localhost interface and port 27017 by default.
At the mongo.exe prompt,issue the following two commands to insert a record in the test collection of the default
test database and then retrieve that record:
db.test.save( { a:1 } )
db.test.find()
See also:
mongo and http://docs.mongodb.org/manualreference/method.If you want to develop applications
using.NET,see the documentation of C#and MongoDB
8
for more information.
8
http://docs.mongodb.org/ecosystem/drivers/csharp
14 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
MongoDB as a Windows Service
New in version 2.0.
You can set up MongoDB as a Windows Service so that the database will start automatically following each reboot
cycle.
Note:mongod.exe added support for running as a Windows service in version 2.0,and mongos.exe added
support for running as a Windows Service in version 2.1.1.
Configure the System The following steps,although optional,are good practice.
You should specify two options when running MongoDB as a Windows Service:a path for the log output (i.e.
logpath) and a configuration file.
1.Optional.Create a specific directory for MongoDB log files:
md C:\mongodb\log
2.Optional.Create a configuration file for the logpath option for MongoDBin the Command Prompt by issuing
this command:
echo logpath=C:\mongodb\log\mongo.log > C:\mongodb\mongod.cfg
Note:Consider setting the logappend option.If you do not,mongod.exe will delete the contents of the existing
log file when starting.
Changed in version 2.2:The default logpath and logappend behavior changed in the 2.2 release.
Install and Run the MongoDB Service Run all of the following commands in Command Prompt with “Adminis-
trative Privileges:”
1.To install the MongoDB service:
C:\mongodb\bin\mongod.exe --config C:\mongodb\mongod.cfg --install
Modify the path to the mongod.cfg file as needed.For the --install option to succeed,you must specify
a logpath setting or the --logpath run-time option.
2.To run the MongoDB service:
net start MongoDB
If you wish to use an alternate path for your dbpath specify it in the config file (e.g.C:\mongodb\mongod.cfg)
on that you specified in the --install operation.You may also specify --dbpath on the command line;however,
always prefer the configuration file.
If you have not set up the data directory,set up the data directory (page 13) where MongoDB will store its data files.
If the dbpath directory does not exist,mongod.exe will not be able to start.The default value for dbpath is
\data\db.
Stop or Remove the MongoDB Service To stop the MongoDB service:
net stop MongoDB
To remove the MongoDB service:
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MongoDB Documentation,Release 2.4.8
C:\mongodb\bin\mongod.exe --remove
1.1.4 MongoDB Enterprise
Install MongoDB Enterprise (page 16)
Install MongoDB Enterprise
New in version 2.2.
MongoDB Enterprise
9
is available on four platforms and contains support for several features related to security and
monitoring.
Required Packages
Changed in version 2.4.4:MongoDB Enterprise uses Cyrus SASL instead of GNU SASL.Earlier 2.4 Enterprise
versions use GNU SASL (libgsasl) instead.For required packages for the earlier 2.4 versions,see Earlier 2.4
Versions (page 16).
To use MongoDB Enterprise,you must install several prerequisites.The names of the packages vary by distribution
and are as follows:
• Debian or Ubuntu 12.04 require:libssl0.9.8,snmp,snmpd,cyrus-sasl2-dbg,
cyrus-sasl2-mit-dbg,libsasl2-2,libsasl2-dev,libsasl2-modules,and
libsasl2-modules-gssapi-mit.Issue a command such as the following to install these pack-
ages:
sudo apt-get install libssl0.9.8 snmp snmpd cyrus-sasl2-dbg cyrus-sasl2-mit-dbg libsasl2-2 libsasl2-dev libsasl2-modules libsasl2-modules-gssapi-mit
• CentOS and Red Hat Enterprise Linux 6.x and 5.x,as well as Amazon Linux AMI require:
net-snmp,net-snmp-libs,openssl,net-snmp-utils,cyrus-sasl,cyrus-sasl-lib,
cyrus-sasl-devel,and cyrus-sasl-gssapi.Issue a command such as the following to install these
packages:
sudo yum install openssl net-snmp net-snmp-libs net-snmp-utils cyrus-sasl cyrus-sasl-lib cyrus-sasl-devel cyrus-sasl-gssapi
• SUSE Enterprise Linux requires libopenssl0_9_8,libsnmp15,slessp1-libsnmp15,
snmp-mibs,cyrus-sasl,cyrus-sasl-devel,and cyrus-sasl-gssapi.Issue a command
such as the following to install these packages:
sudo zypper install libopenssl0_9_8 libsnmp15 slessp1-libsnmp15 snmp-mibs cyrus-sasl cyrus-sasl-devel cyrus-sasl-gssapi
Earlier 2.4 Versions Before version 2.4.4,the 2.4 versions of MongoDB Enterprise use libgsasl
10
.The required
packages for the different distributions are as follows:
• Ubuntu 12.04 requires libssl0.9.8,libgsasl,snmp,and snmpd.Issue a command such as the follow-
ing to install these packages:
sudo apt-get install libssl0.9.8 libgsasl7 snmp snmpd
9
http://www.mongodb.com/products/mongodb-enterprise
10
http://www.gnu.org/software/gsasl/
16 Chapter 1.Install MongoDB
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• Red Hat Enterprise Linux 6.x series and Amazon Linux AMI require openssl,libgsasl7,net-snmp,
net-snmp-libs,and net-snmp-utils.To download libgsasl you must enable the EPEL repository
by issuing the following sequence of commands to add and update the systemrepositories:
sudo rpm -ivh http://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
sudo yum update -y
When you have installed and updated the EPEL repositories,issue the following install these packages:
sudo yum install openssl net-snmp net-snmp-libs net-snmp-utils libgsasl
• SUSE Enterprise Linux requires libopenssl0_9_8,libsnmp15,slessp1-libsnmp15,and
snmp-mibs.Issue a command such as the following to install these packages:
sudo zypper install libopenssl0_9_8 libsnmp15 slessp1-libsnmp15 snmp-mibs
Note:Before 2.4.4,MongoDB Enterprise 2.4 for SUSE requires libgsasl
11
which is not available in the default
repositories for SUSE.
Install MongoDB Enterprise Binaries
When you have installed the required packages,and downloaded the Enterprise packages
12
you can install the packages
using the same procedure as a standard installation of MongoDB on Linux Systems (page 9).
Note:.deb and.rpm packages for Enterprise releases are available for some platforms.You can use these to install
MongoDB directly using the dpkg and rpm utilities.
Use the sequence of commands below to download and extract MongoDB Enterprise packages appropriate for your
distribution:
Ubuntu 12.04
curl -O http://downloads.10gen.com/linux/mongodb-linux-x86_64-subscription-ubuntu1204-2.5.4.tgz
tar -zxvf mongodb-linux-x86_64-subscription-ubuntu1204-2.5.4.tgz
cp -R -n mongodb-linux-x86_64-subscription-ubuntu1204-2.5.4/mongodb
Red Hat Enterprise Linux 6.x
curl -O http://downloads.10gen.com/linux/mongodb-linux-x86_64-subscription-rhel62-2.5.4.tgz
tar -zxvf mongodb-linux-x86_64-subscription-rhel62-2.5.4.tgz
cp -R -n mongodb-linux-x86_64-subscription-rhel62-2.5.4/mongodb
Amazon Linux AMI
curl -O http://downloads.10gen.com/linux/mongodb-linux-x86_64-subscription-amzn64-2.5.4.tgz
tar -zxvf mongodb-linux-x86_64-subscription-amzn64-2.5.4.tgz
cp -R -n mongodb-linux-x86_64-subscription-amzn64-2.5.4/mongodb
11
http://www.gnu.org/software/gsasl/
12
http://www.mongodb.com/products/mongodb-enterprise
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MongoDB Documentation,Release 2.4.8
SUSE Enterprise Linux
curl -O http://downloads.10gen.com/linux/mongodb-linux-x86_64-subscription-suse11-2.5.4.tgz
tar -zxvf mongodb-linux-x86_64-subscription-suse11-2.5.4.tgz
cp -R -n mongodb-linux-x86_64-subscription-suse11-2.5.4/mongodb
Running and Using MongoDB
Note:The Enterprise packages currently include an example SNMP configuration file named mongod.conf.This
file is not a MongoDB configuration file.
Before you start mongod for the first time,you will need to create the data directory (i.e.dbpath).By default,
mongod writes data to the/data/db directory.
Step 1:Create dbpath To create the default dbpath directory,use the following command:
mkdir -p/data/db
Step 2:Set dbpath Permissions Ensure that the user that runs the mongod process has read and write permissions
to this directory.For example,if you will run the mongod process,change the owner of the/data/db directory:
chown mongodb/data/db
You must create the mongodb user separately.
You can specify an alternate path for data files using the --dbpath option to mongod.If you use an alternate
location for your data directory,ensure that this user can write to the alternate data directory.
Start MongoDB To start mongod,run the executable mongod at the systemprompt.
For example,if your PATH includes the location of the mongod binary,enter mongod at the systemprompt.
mongod
If your PATH does not include the location of the mongod binary,enter the full path to the mongod binary.
Starting mongod without any arguments starts a MongoDB instance that writes data to the/data/db directory.To
specify an alternate data directory,start mongod with the --dbpath option:
mongod --dbpath <some alternate directory>
Whether using the default/data/db or an alternate directory,ensure that the user account running mongod has read
and write permissions to the directory.
Stop MongoDB To stop the mongod instance,press Control+C in the terminal where the mongod instance is
running.
Further Reading
As you begin to use MongoDB,consider the Getting Started with MongoDB (page 19) and MongoDB Tutorials
(page 186) resources.To read about features only available in MongoDB Enterprise,consider:Monitor MongoDB
with SNMP (page 176) and Deploy MongoDB with Kerberos Authentication (page 261).
18 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
1.2 First Steps with MongoDB
After you have installed MongoDB,consider the following documents as you begin to learn about MongoDB:
Getting Started with MongoDB (page 19) An introduction to the basic operation and use of MongoDB.
Generate Test Data (page 23) To support initial exploration,generate test data to facilitate testing.
1.2.1 Getting Started with MongoDB
This tutorial addresses the following aspects of MongoDB use:
• Connect to a Database (page 19)
– Connect to a mongod (page 19)
– Select a Database (page 20)
– Display mongo Help (page 20)
• Create a Collection and Insert Documents (page 20)
• Insert Documents using a For Loop or a JavaScript Function (page 21)
• Working with the Cursor (page 21)
– Iterate over the Cursor with a Loop (page 21)
– Use Array Operations with the Cursor (page 22)
– Query for Specific Documents (page 22)
– Return a Single Document froma Collection (page 23)
– Limit the Number of Documents in the Result Set (page 23)
• Next Steps with MongoDB (page 23)
This tutorial provides an introduction to basic database operations using the mongo shell.mongo is a part of the
standard MongoDB distribution and provides a full JavaScript environment with a complete access to the JavaScript
language and all standard functions as well as a full database interface for MongoDB.See the mongo JavaScript API
13
documentation and the mongo shell JavaScript Method Reference.
The tutorial assumes that you’re running MongoDB on a Linux or OS Xoperating systemand that you have a running
database server;MongoDB does support Windows and provides a Windows distribution with identical operation.
For instructions on installing MongoDB and starting the database server,see the appropriate installation (page 3)
document.
Connect to a Database
In this section,you connect to the database server,which runs as mongod,and begin using the mongo shell to select
a logical database within the database instance and access the help text in the mongo shell.
Connect to a mongod
Froma systemprompt,start mongo by issuing the mongo command,as follows:
mongo
By default,mongo looks for a database server listening on port 27017 on the localhost interface.To connect to
a server on a different port or interface,use the --port and --host options.
13
http://api.mongodb.org/js
1.2.First Steps with MongoDB 19
MongoDB Documentation,Release 2.4.8
Select a Database
After starting the mongo shell your session will use the test database by default.At any time,issue the following
operation at the mongo to report the name of the current database:
db
1.Fromthe mongo shell,display the list of databases,with the following operation:
show dbs
2.Switch to a new database named mydb,with the following operation:
use mydb
3.Confirm that your session has the mydb database as context,by checking the value of the db object,which
returns the name of the current database,as follows:
db
At this point,if you issue the show dbs operation again,it will not include the mydb database.MongoDB
will not permanently create a database until you insert data into that database.The Create a Collection and
Insert Documents (page 20) section describes the process for inserting data.
New in version 2.4:show databases also returns a list of databases.
Display mongo Help
At any point,you can access help for the mongo shell using the following operation:
help
Furthermore,you can append the.help() method to some JavaScript methods,any cursor object,as well as the db
and db.collection objects to return additional help information.
Create a Collection and Insert Documents
In this section,you insert documents into a newcollection named testData within the new database named mydb.
MongoDB will create a collection implicitly upon its first use.You do not need to create a collection before inserting
data.Furthermore,because MongoDB uses dynamic schemas (page 576),you also need not specify the structure of
your documents before inserting theminto the collection.
1.Fromthe mongo shell,confirmyou are in the mydb database by issuing the following:
db
2.If mongo does not return mydb for the previous operation,set the context to the mydb database,with the
following operation:
use mydb
3.Create two documents named j and k by using the following sequence of JavaScript operations:
j = { name:"mongo"}
k = { x:3 }
4.Insert the j and k documents into the testData collection with the following sequence of operations:
20 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
db.testData.insert( j )
db.testData.insert( k )
When you insert the first document,the mongod will create both the mydb database and the testData
collection.
5.Confirmthat the testData collection exists.Issue the following operation:
show collections
The mongo shell will return the list of the collections in the current (i.e.mydb) database.At this point,the only
collection is testData.All mongod databases also have a system.indexes (page 228) collection.
6.Confirm that the documents exist in the testData collection by issuing a query on the collection using the
find() method:
db.testData.find()
This operation returns the following results.The ObjectId (page 129) values will be unique:
{"_id":ObjectId("4c2209f9f3924d31102bd84a"),"name":"mongo"}
{"_id":ObjectId("4c2209fef3924d31102bd84b"),"x":3 }
All MongoDB documents must have an _id field with a unique value.These operations do not explicitly
specify a value for the _id field,so mongo creates a unique ObjectId (page 129) value for the field before
inserting it into the collection.
Insert Documents using a For Loop or a JavaScript Function
To perform the remaining procedures in this tutorial,first add more documents to your database using one or both of
the procedures described in Generate Test Data (page 23).
Working with the Cursor
When you query a collection,MongoDB returns a “cursor” object that contains the results of the query.The mongo
shell then iterates over the cursor to display the results.Rather than returning all results at once,the shell iterates over
the cursor 20 times to display the first 20 results and then waits for a request to iterate over the remaining results.In
the shell,use enter it to iterate over the next set of results.
The procedures in this section show other ways to work with a cursor.For comprehensive documentation on cursors,
see crud-read-cursor.
Iterate over the Cursor with a Loop
Before using this procedure,make sure to add at least 25 documents to a collection using one of the procedures in
Generate Test Data (page 23).You can name your database and collections anything you choose,but this procedure
will assume the database named test and a collection named testData.
1.In the MongoDB JavaScript shell,query the testData collection and assign the resulting cursor object to the
c variable:
var c = db.testData.find()
2.Print the full result set by using a while loop to iterate over the c variable:
1.2.First Steps with MongoDB 21
MongoDB Documentation,Release 2.4.8
while ( c.hasNext() ) printjson( c.next() )
The hasNext() function returns true if the cursor has documents.The next() method returns the next
document.The printjson() method renders the document in a JSON-like format.
The operation displays 20 documents.For example,if the documents have a single field named x,the operation
displays the field as well as each document’s ObjectId:
{"_id":ObjectId("51a7dc7b2cacf40b79990be6"),"x":1 }
{"_id":ObjectId("51a7dc7b2cacf40b79990be7"),"x":2 }
{"_id":ObjectId("51a7dc7b2cacf40b79990be8"),"x":3 }
{"_id":ObjectId("51a7dc7b2cacf40b79990be9"),"x":4 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bea"),"x":5 }
{"_id":ObjectId("51a7dc7b2cacf40b79990beb"),"x":6 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bec"),"x":7 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bed"),"x":8 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bee"),"x":9 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bef"),"x":10 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf0"),"x":11 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf1"),"x":12 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf2"),"x":13 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf3"),"x":14 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf4"),"x":15 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf5"),"x":16 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf6"),"x":17 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf7"),"x":18 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf8"),"x":19 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf9"),"x":20 }
Use Array Operations with the Cursor
The following procedure lets you manipulate a cursor object as if it were an array:
1.In the mongo shell,query the testData collection and assign the resulting cursor object to the c variable:
var c = db.testData.find()
2.To find the document at the array index 4,use the following operation:
printjson( c [ 4 ] )
MongoDB returns the following:
{"_id":ObjectId("51a7dc7b2cacf40b79990bea"),"x":5 }
When you access documents in a cursor using the array index notation,mongo first calls the
cursor.toArray() method and loads into RAM all documents returned by the cursor.The index is then
applied to the resulting array.This operation iterates the cursor completely and exhausts the cursor.
For very large result sets,mongo may run out of available memory.
For more information on the cursor,see crud-read-cursor.
Query for Specific Documents
MongoDB has a rich query system that allows you to select and filter the documents in a collection along specific
fields and values.See Query Documents (page 60) and Read Operations (page 31) for a full account of queries in
MongoDB.
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MongoDB Documentation,Release 2.4.8
In this procedure,you query for specific documents in the testData collection by passing a “query document” as a
parameter to the find() method.Aquery document specifies the criteria the query must match to return a document.
In the mongo shell,query for all documents where the x field has a value of 18 by passing the { x:18 } query
document as a parameter to the find() method:
db.testData.find( { x:18 } )
MongoDB returns one document that fits this criteria:
{"_id":ObjectId("51a7dc7b2cacf40b79990bf7"),"x":18 }
Return a Single Document froma Collection
With the findOne() method you can return a single document from a MongoDB collection.The findOne()
method takes the same parameters as find(),but returns a document rather than a cursor.
To retrieve one document fromthe testData collection,issue the following command:
db.testData.findOne()
For more information on querying for documents,see the Query Documents (page 60) and Read Operations (page 31)
documentation.
Limit the Number of Documents in the Result Set
To increase performance,you can constrain the size of the result by limiting the amount of data your application must
receive over the network.
To specify the maximum number of documents in the result set,call the limit() method on a cursor,as in the
following command:
db.testData.find().limit(3)
MongoDB will return the following result,with different ObjectId (page 129) values:
{"_id":ObjectId("51a7dc7b2cacf40b79990be6"),"x":1 }
{"_id":ObjectId("51a7dc7b2cacf40b79990be7"),"x":2 }
{"_id":ObjectId("51a7dc7b2cacf40b79990be8"),"x":3 }
Next Steps with MongoDB
For more information on manipulating the documents in a database as you continue to learn MongoDB,consider the
following resources:
• MongoDB CRUD Operations (page 27)
• SQL to MongoDB Mapping Chart (page 85)
• MongoDB Drivers and Client Libraries (page 95)
1.2.2 Generate Test Data
This tutorial describes how to quickly generate test data as you need to test basic MongoDB operations.
1.2.First Steps with MongoDB 23
MongoDB Documentation,Release 2.4.8
Insert Multiple Documents Using a For Loop
You can add documents to a new or existing collection by using a JavaScript for loop run fromthe mongo shell.
1.From the mongo shell,insert new documents into the testData collection using the following for loop.If
the testData collection does not exist,MongoDB creates the collection implicitly.
for (var i = 1;i <= 25;i++) db.testData.insert( { x:i } )
2.Use find() to query the collection:
db.testData.find()
The mongo shell displays the first 20 documents in the collection.Your ObjectId (page 129) values will be
different:
{"_id":ObjectId("51a7dc7b2cacf40b79990be6"),"x":1 }
{"_id":ObjectId("51a7dc7b2cacf40b79990be7"),"x":2 }
{"_id":ObjectId("51a7dc7b2cacf40b79990be8"),"x":3 }
{"_id":ObjectId("51a7dc7b2cacf40b79990be9"),"x":4 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bea"),"x":5 }
{"_id":ObjectId("51a7dc7b2cacf40b79990beb"),"x":6 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bec"),"x":7 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bed"),"x":8 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bee"),"x":9 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bef"),"x":10 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf0"),"x":11 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf1"),"x":12 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf2"),"x":13 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf3"),"x":14 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf4"),"x":15 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf5"),"x":16 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf6"),"x":17 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf7"),"x":18 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf8"),"x":19 }
{"_id":ObjectId("51a7dc7b2cacf40b79990bf9"),"x":20 }
1.The find() returns a cursor.To iterate the cursor and return more documents use the it operation in the
mongo shell.The mongo shell will exhaust the cursor,and return the following documents:
{"_id":ObjectId("51a7dce92cacf40b79990bfc"),"x":21 }
{"_id":ObjectId("51a7dce92cacf40b79990bfd"),"x":22 }
{"_id":ObjectId("51a7dce92cacf40b79990bfe"),"x":23 }
{"_id":ObjectId("51a7dce92cacf40b79990bff"),"x":24 }
{"_id":ObjectId("51a7dce92cacf40b79990c00"),"x":25 }
Insert Multiple Documents with a mongo Shell Function
You can create a JavaScript function in your shell session to generate the above data.The insertData() JavaScript
function,shown here,creates new data for use in testing or training by either creating a new collection or appending
data to an existing collection:
function insertData(dbName,colName,num) {
var col = db.getSiblingDB(dbName).getCollection(colName);
for (i = 0;i < num;i++) {
col.insert({x:i});
24 Chapter 1.Install MongoDB
MongoDB Documentation,Release 2.4.8
}
print(col.count());
}
The insertData() function takes three parameters:a database,a new or existing collection,and the number of
documents to create.The function creates documents with an x field that is set to an incremented integer,as in the
following example documents:
{"_id":ObjectId("51a4da9b292904caffcff6eb"),"x":0 }
{"_id":ObjectId("51a4da9b292904caffcff6ec"),"x":1 }
{"_id":ObjectId("51a4da9b292904caffcff6ed"),"x":2 }
Store the function in your.mongorc.js file.The mongo shell loads the function for you every time you start a session.
Example
Specify database name,collection name,and the number of documents to insert as arguments to insertData().
insertData("test","testData",400)
This operation inserts 400 documents into the testData collection in the test database.If the collection and
database do not exist,MongoDB creates themimplicitly before inserting documents.
See also:
MongoDB CRUD Concepts (page 29) and Data Models (page 97).
1.2.First Steps with MongoDB 25
MongoDB Documentation,Release 2.4.8
26 Chapter 1.Install MongoDB
CHAPTER 2
MongoDB CRUD Operations
MongoDB provides rich semantics for reading and manipulating data.CRUD stands for create,read,update,and
delete.These terms are the foundation for all interactions with the database.
MongoDB CRUD Introduction (page 27) An introduction to the MongoDB data model as well as queries and data
manipulations.
MongoDB CRUD Concepts (page 29) The core documentation of query and data manipulation.
MongoDB CRUD Tutorials (page 58) Examples of basic query and data modification operations.
MongoDB CRUD Reference (page 82) Reference material for the query and data manipulation interfaces.
2.1 MongoDB CRUD Introduction
MongoDB stores data in the formof documents,which are JSON-like field and value pairs.Documents are analogous
to structures in programming languages that associate keys with values,where keys may hold other pairs of keys and
values (e.g.dictionaries,hashes,maps,and associative arrays).Formally,MongoDBdocuments are BSON documents,
which is a binary representation of JSON with additional type information.For more information,see Documents
(page 122).
Figure 2.1:A MongoDB document.
MongoDB stores all documents in collections.A collection is a group of related documents that have a set of shared
common indexes.Collections are analogous to a table in relational databases.
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Figure 2.2:A collection of MongoDB documents.
2.1.1 Database Operations
Query
In MongoDB a query targets a specific collection of documents.Queries specify criteria,or conditions,that identify
the documents that MongoDB returns to the clients.A query may include a projection that specifies the fields from
the matching documents to return.You can optionally modify queries to impose limits,skips,and sort orders.
In the following diagram,the query process specifies a query criteria and a sort modifier:
Data Modification
Data modification refers to operations that create,update,or delete data.In MongoDB,these operations modify the
data of a single collection.For the update and delete operations,you can specify the criteria to select the documents
to update or remove.
In the following diagram,the insert operation adds a new document to the users collection.
2.1.2 Related Features
Indexes
To enhance the performance of common queries and updates,MongoDBhas full support for secondary indexes.These
indexes allowapplications to store a viewof a portion of the collection in an efficient data structure.Most indexes store
an ordered representation of all values of a field or a group of fields.Indexes may also enforce uniqueness (page 334),
store objects in a geospatial representation (page 326),and facilitate text search (page 332).
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Figure 2.3:The stages of a MongoDB query with a query criteria and a sort modifier.
Read Preference
For replica sets and sharded clusters with replica set components,applications specify read preferences (page 405).A
read preference determines how the client direct read operations to the set.
Write Concern
Applications can also control the behavior of write operations using write concern (page 46).Particularly useful
for deployments with replica sets,the write concern semantics allow clients to specify the assurance that MongoDB
provides when reporting on the success of a write operation.
Aggregation
In addition to the basic queries,MongoDB provides several data aggregation features.For example,MongoDB can
return counts of the number of documents that match a query,or return the number of distinct values for a field,or
process a collection of documents using a versatile stage-based data processing pipeline or map-reduce operations.
2.2 MongoDB CRUD Concepts
The Read Operations (page 31) and Write Operations (page 42) documents introduces the behavior and operations of
read and write operations for MongoDB deployments.
Read Operations (page 31) Introduces all operations that select and return documents to clients,including the query
specifications.
Cursors (page 35) Queries return iterable objects,called cursors,that hold the full result set of the query re-
quest.
Query Optimization (page 36) Analyze and improve query performance.
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Figure 2.4:The stages of a MongoDB insert operation.
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Distributed Queries (page 38) Describes how sharded clusters and replica sets affect the performance of read
operations.
Write Operations (page 42) Introduces data create and modify operations,their behavior,and performances.
Write Concern (page 46) Describes the kind of guarantee MongoDB provides when reporting on the success
of a write operation.
Distributed Write Operations (page 49) Describes howMongoDB directs write operations on sharded clusters
and replica sets and the performance characteristics of these operations.
2.2.1 Read Operations
Read operations,or queries,retrieve data stored in the database.In MongoDB,queries select documents froma single
collection.
Queries specify criteria,or conditions,that identify the documents that MongoDB returns to the clients.A query may
include a projection that specifies the fields fromthe matching documents to return.The projection limits the amount
of data that MongoDB returns to the client over the network.
Query Interface
For query operations,MongoDB provide a db.collection.find() method.The method accepts both the query
criteria and projections and returns a cursor (page 35) to the matching documents.You can optionally modify the
query to impose limits,skips,and sort orders.
The following diagramhighlights the components of a MongoDB query operation:
Figure 2.5:The components of a MongoDB find operation.
The next diagramshows the same query in SQL:
Figure 2.6:The components of a SQL SELECT statement.
Example
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db.users.find( { age:{ $gt:18 } },{ name:1,address:1 } ).limit(5)
This query selects the documents in the users collection that match the condition age is greater than 18.To specify
the greater than condition,query criteria uses the greater than (i.e.$gt) query selection operator.The query returns
at most 5 matching documents (or more precisely,a cursor to those documents).The matching documents will return
with only the _id,name and address fields.See Projections (page 32) for details.
See
SQL to MongoDB Mapping Chart (page 85) for additional examples of MongoDBqueries and the corresponding SQL
statements.
Query Behavior
MongoDB queries exhibit the following behavior:
• All queries in MongoDB address a single collection.
• You can modify the query to impose limits,skips,and sort orders.
• The order of documents returned by a query is not defined and is not necessarily consistent unless you specify a
sort().
• Operations that modify existing documents (page 67) (i.e.updates) use the same query syntax as queries to select
documents to update.
• In aggregation (page 281) pipeline,the $match pipeline stage provides access to MongoDB queries.
MongoDB provides a db.collection.findOne() method as a special case of find() that returns a single
document.
Query Statements
Consider the following diagramof the query process that specifies a query criteria and a sort modifier:
In the diagram,the query selects documents fromthe users collection.Using a query selection operator
to define the conditions for matching documents,the query selects documents that have age greater than (i.e.$gt)
18.Then the sort() modifier sorts the results by age in ascending order.
For additional examples of queries,see Query Documents (page 60).
Projections
Queries in MongoDBreturn all fields in all matching documents by default.To limit the amount of data that MongoDB
sends to applications,include a projection in the queries.By projecting results with a subset of fields,applications
reduce their network overhead and processing requirements.
Projections,which are the the second argument to the find() method,may either specify a list of fields to return or
list fields to exclude in the result documents.
Important:Except for excluding the _id field in inclusive projections,you cannot mix exclusive and inclusive
projections.
Consider the following diagramof the query process that specifies a query criteria and a projection:
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Figure 2.7:The stages of a MongoDB query with a query criteria and a sort modifier.
Figure 2.8:The stages of a MongoDB query with a query criteria and projection.MongoDB only transmits the
projected data to the clients.
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In the diagram,the query selects fromthe users collection.The criteria matches the documents that have age equal
to 18.Then the projection specifies that only the name field should return in the matching documents.
Projection Examples
Exclude One Field Froma Result Set
db.records.find( {"user_id":{ $lt:42} },{ history:0} )
This query selects a number of documents in the records collection that match the query {"user_id":{
$lt:42} },but excludes the history field.
Return Two fields and the _id Field
db.records.find( {"user_id":{ $lt:42} },{"name":1,"email":1} )
This query selects a number of documents in the records collection that match the query {"user_id":{
$lt:42} },but returns documents that have the _id field (implicitly included) as well as the name and email
fields.
Return Two Fields and Exclude _id
db.records.find( {"user_id":{ $lt:42} },{"_id":0,"name":1,"email":1 } )
This query selects a number of documents in the records collection that match the query {"user_id":{
$lt:42} },but only returns the name and email fields.
See
Limit Fields to Return from a Query (page 63) for more examples of queries with projection statements.
Projection Behavior
MongoDB projections have the following properties:
• In MongoDB,the _id field is always included in results unless explicitly excluded.
• For fields that contain arrays,MongoDB provides the following projection operators:$elemMatch,$slice,
$.
• For related projection functionality in the aggregation framework (page 281) pipeline,use the $project
pipeline stage.
Related Concepts
The following documents further describe read operations:
Cursors (page 35) Queries return iterable objects,called cursors,that hold the full result set of the query request.
Query Optimization (page 36) Analyze and improve query performance.
Query Plans (page 37) MongoDB processes and executes using plans developed to return results as efficiently as
possible.
Distributed Queries (page 38) Describes how sharded clusters and replica sets affect the performance of read opera-
tions.
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Cursors
In the mongo shell,the primary method for the read operation is the db.collection.find() method.This
method queries a collection and returns a cursor to the returning documents.
To access the documents,you need to iterate the cursor.However,in the mongo shell,if the returned cursor is not
assigned to a variable using the var keyword,then the cursor is automatically iterated up to 20 times
1
to print up to
the first 20 documents in the results.
For example,in the mongo shell,the following read operation queries the inventory collection for documents that
have type equal to ’food’ and automatically print up to the first 20 matching documents:
db.inventory.find( { type:'food'} );
To manually iterate the cursor to access the documents,see Iterate a Cursor in the mongo Shell (page 65).
Cursor Behaviors
Closure of Inactive Cursors By default,the server will automatically close the cursor after 10 minutes of inactivity
or if client has exhausted the cursor.To override this behavior,you can specify the noTimeout wire protocol flag
2
in your query;however,you should either close the cursor manually or exhaust the cursor.In the mongo shell,you
can set the noTimeout flag:
var myCursor = db.inventory.find().addOption(DBQuery.Option.noTimeout);
See your driver (page 95) documentation for information on setting the noTimeout flag.For the mongo shell,see
cursor.addOption() for a complete list of available cursor flags.
Cursor Isolation Because the cursor is not isolated during its lifetime,intervening write operations on a document
may result in a cursor that returns a document more than once if that document has changed.To handle this situation,
see the information on snapshot mode (page 586).
Cursor Batches The MongoDB server returns the query results in batches.Batch size will not exceed the maximum
BSON document size.For most queries,the first batch returns 101 documents or just enough documents to exceed 1
megabyte.Subsequent batch size is 4 megabytes.To override the default size of the batch,see batchSize() and
limit().
For queries that include a sort operation without an index,the server must load all the documents in memory to perform
the sort and will return all documents in the first batch.
As you iterate through the cursor and reach the end of the returned batch,if there are more results,cursor.next()
will perform a getmore operation to retrieve the next batch.To see how many documents remain in the batch
as you iterate the cursor,you can use the objsLeftInBatch() method,as in the following example:
var myCursor = db.inventory.find();
var myFirstDocument = myCursor.hasNext()?myCursor.next():null;
myCursor.objsLeftInBatch();
1
You can use the DBQuery.shellBatchSize to change the number of iteration from the default value 20.See Executing Queries
(page 214) for more information.
2
http://docs.mongodb.org/meta-driver/latest/legacy/mongodb-wire-protocol
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Cursor Information You can use the command cursorInfo to retrieve the following information on cursors:
• total number of open cursors
• size of the client cursors in current use
• number of timed out cursors since the last server restart
Consider the following example:
db.runCommand( { cursorInfo:1 } )
The result fromthe command returns the following document:
{
"totalOpen":<number>,
"clientCursors_size":<number>,
"timedOut":<number>,
"ok":1
}
Query Optimization
Indexes improve the efficiency of read operations by reducing the amount of data that query operations need to process.
This simplifies the work associated with fulfilling queries within MongoDB.
Create an Index to Support Read Operations If your application queries a collection on a particular field or fields,
then an index on the queried field or fields can prevent the query from scanning the whole collection to find and
return the query results.For more information about indexes,see the complete documentation of indexes in MongoDB
(page 318).
Example
An application queries the inventory collection on the type field.The value of the type field is user-driven.
var typeValue = <someUserInput>;
db.inventory.find( { type:typeValue } );
To improve the performance of this query,add an ascending,or a descending,index to the inventory collection
on the type field.
3
In the mongo shell,you can create indexes using the db.collection.ensureIndex()
method:
db.inventory.ensureIndex( { type:1 } )
This index can prevent the above query on type fromscanning the whole collection to return the results.
To analyze the performance of the query with an index,see Analyze Query Performance (page 66).
In addition to optimizing read operations,indexes can support sort operations and allow for a more efficient storage
utilization.See db.collection.ensureIndex()and Indexing Tutorials (page 338) for more information about
index creation.
3
For single-field indexes,the selection between ascending and descending order is immaterial.For compound indexes,the selection is important.
See indexing order (page 323) for more details.
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Query Selectivity Some query operations are not selective.These operations cannot use indexes effectively or
cannot use indexes at all.
The inequality operators $nin and $ne are not very selective,as they often match a large portion of the index.As a
result,in most cases,a $nin or $ne query with an index may performno better than a $nin or $ne query that must
scan all documents in a collection.
Queries that specify regular expressions,with inline JavaScript regular expressions or $regex operator expressions,
cannot use an index with one exception.Queries that specify regular expression with anchors at the beginning of a
string can use an index.
Covering a Query An index covers (page 369) a query,a covered query,when:
• all the fields in the query (page 60) are part of that index,and
• all the fields returned in the documents that match the query are in the same index.
For these queries,MongoDB does not need to inspect documents outside of the index.This is often more efficient
than inspecting entire documents.
Example
Given a collection inventory with the following index on the type and item fields:
{ type:1,item:1 }
This index will cover the following query on the type and item fields,which returns only the item field:
db.inventory.find( { type:"food",item:/^c/},
{ item:1,_id:0 } )
However,the index will not cover the following query,which returns the item field and the _id field:
db.inventory.find( { type:"food",item:/^c/},
{ item:1 } )
See Create Indexes that Support Covered Queries (page 369) for more information on the behavior and use of covered
queries.
Query Plans
The MongoDBquery optimizer processes queries and chooses the most efficient query plan for a query given the avail-
able indexes.The query systemthen uses this query plan each time the query runs.The query optimizer occasionally
reevaluates query plans as the content of the collection changes to ensure optimal query plans.
You can use the explain() method to view statistics about the query plan for a given query.This information can
help as you develop indexing strategies (page 367).
Query Optimization To create a new query plan,the query optimizer:
1.runs the query against several candidate indexes in parallel.
2.records the matches in a common results buffer or buffers.
• If the candidate plans include only ordered query plans,there is a single common results buffer.
• If the candidate plans include only unordered query plans,there is a single common results buffer.
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• If the candidate plans include both ordered query plans and unordered query plans,there are two common
results buffers,one for the ordered plans and the other for the unordered plans.
If an index returns a result already returned by another index,the optimizer skips the duplicate match.In the
case of the two buffers,both buffers are de-duped.
3.stops the testing of candidate plans and selects an index when one of the following events occur:
• An unordered query plan has returned all the matching results;or
• An ordered query plan has returned all the matching results;or
• An ordered query plan has returned a threshold number of matching results:
– Version 2.0:Threshold is the query batch size.The default batch size is 101.
– Version 2.2:Threshold is 101.
The selected index becomes the index specified in the query plan;future iterations of this query or queries with the
same query pattern will use this index.Query pattern refers to query select conditions that differ only in the values,as
in the following two queries with the same query pattern:
db.inventory.find( { type:'food'} )
db.inventory.find( { type:'utensil'} )
Query Plan Revision As collections change over time,the query optimizer deletes the query plan and re-evaluates
after any of the following events:
• The collection receives 1,000 write operations.
• The reIndex rebuilds the index.
• You add or drop an index.
• The mongod process restarts.
Distributed Queries
Read Operations to Sharded Clusters Sharded clusters allow you to partition a data set among a cluster of
mongod instances in a way that is nearly transparent to the application.For an overview of sharded clusters,see
the Sharding (page 491) section of this manual.
For a sharded cluster,applications issue operations to one of the mongos instances associated with the cluster.
Read operations on sharded clusters are most efficient when directed to a specific shard.Queries to sharded collections
should include the collection’s shard key (page 503).When a query includes a shard key,the mongos can use cluster
metadata fromthe config database (page 500) to route the queries to shards.
If a query does not include the shard key,the mongos must direct the query to all shards in the cluster.These scatter
gather queries can be inefficient.On larger clusters,scatter gather queries are unfeasible for routine operations.
For more information on read operations in sharded clusters,see the Sharded Cluster Query Routing (page 507) and
Shard Keys (page 503) sections.
Read Operations to Replica Sets Replica sets use read preferences to determine where and how to route read
operations to members of the replica set.By default,MongoDB always reads data from a replica set’s primary.You
can modify that behavior by changing the read preference mode (page 488).
You can configure the read preference mode (page 488) on a per-connection or per-operation basis to allowreads from
secondaries to:
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Figure 2.9:Diagramof a sharded cluster.
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Figure 2.10:Read operations to a sharded cluster.Query criteria includes the shard key.The query router mongos
can target the query to the appropriate shard or shards.
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Figure 2.11:Read operations to a sharded cluster.Query criteria does not include the shard key.The query router
mongos must broadcast query to all shards for the collection.
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• reduce latency in multi-data-center deployments,
• improve read throughput by distributing high read-volumes (relative to write volume),
• for backup operations,and/or
• to allow reads during failover (page 396) situations.
Figure 2.12:Read operations to a replica set.Default read preference routes the read to the primary.Read preference
of nearest routes the read to the nearest member.
Read operations fromsecondary members of replica sets are not guaranteed to reflect the current state of the primary,
and the state of secondaries will trail the primary by some amount of time.Often,applications don’t rely on this kind
of strict consistency,but application developers should always consider the needs of their application before setting
read preference.
For more information on read preference or on the read preference modes,see Read Preference (page 405) and Read
Preference Modes (page 488).
2.2.2 Write Operations
A write operation is any operation that creates or modifies data in the MongoDB instance.In MongoDB,write
operations target a single collection.All write operations in MongoDB are atomic on the level of a single document.
There are three classes of write operations in MongoDB:insert,update,and remove.Insert operations add newdata to
a collection.Update operations modify existing data,and remove operations delete data from a collection.No insert,
update,or remove can affect more than one document atomically.
For the update and remove operations,you can specify criteria,or conditions,that identify the documents to update or
remove.These operations use the same query syntax to specify the criteria as read operations (page 31).
After issuing these modification operations,MongoDB allows applications to determine the level of acknowledgment
returned fromthe database.See Write Concern (page 46).
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Create
Create operations add new documents to a collection.In MongoDB,the db.collection.insert() method
performs create operations.
The following diagramhighlights the components of a MongoDB insert operation:
Figure 2.13:The components of a MongoDB insert operations.
The following diagramshows the same query in SQL:
Figure 2.14:The components of a SQL INSERT statement.
Example
The following operation inserts a newdocuments into the users collection.The newdocument has four fields name,
age,and status,and an _id field.MongoDB always adds the _id field to the new document if that field does not
exist.
db.users.insert(
{
name:"sue",
age:26,
status:"A"
}
)
This operation inserts a new document into the users collection.The new document has four fields:name,age,
status,and an _id field.MongoDB always adds the _id field to a new document if the field does not exist.
For more information,see db.collection.insert() and Insert Documents (page 59).
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Some updates also create records.If an update operation specifies the upsert flag and there are no documents that
match the query portion of the update operation,then MongoDB will convert the update into an insert.
With an upsert,applications can decide between performing an update or an insert operation using just a single call.
Both the update() method and the save() method can perform an upsert.See update() and save() for
details on performing an upsert with these methods.
See
SQL to MongoDB Mapping Chart (page 85) for additional examples of MongoDB write operations and the corre-
sponding SQL statements.
Insert Behavior
If you add a new document without the _id field,the client library or the mongod instance adds an _id field and
populates the field with a unique ObjectId.
If you specify the _id field,the value must be unique within the collection.For operations with write concern
(page 46),if you try to create a document with a duplicate _id value,mongod returns a duplicate key exception.
Update
Update operations modify existing documents in a collection.In MongoDB,db.collection.update() and the
db.collection.save() methods performupdate operations.The db.collection.update() method can
accept a query criteria to determine which documents to update as well as an option to update multiple rows.The
method can also accept options that affect its behavior such as the multi option to update multiple documents.
The following diagramhighlights the components of a MongoDB update operation:
Figure 2.15:The components of a MongoDB update operation.
The following diagramshows the same query in SQL:
Figure 2.16:The components of a SQL UPDATE statement.
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Example
db.users.update(
{ age:{ $gt:18 } },
{ $set:{ status:"A"} },
{ multi:true }
)
This update operation on the users collection sets the status field to A for the documents that match the criteria
of age greater than 18.
For more information,see db.collection.update() and db.collection.save(),and Modify Docu-
ments (page 67) for examples.
Update Behavior
By default,the db.collection.update()method updates a single document.However,with the multioption,
update() can update all documents in a collection that match a query.
The db.collection.update() method either updates specific fields in the existing document or replaces the
document.See db.collection.update() for details.
When performing update operations that increase the document size beyond the allocated space for that document,the
update operation relocates the document on disk and may reorder the document fields depending on the type of update.
The db.collection.save() method replaces a document and can only update a single document.See
db.collection.save() and Insert Documents (page 59) for more information
Delete
Delete operations remove documents from a collection.In MongoDB,db.collection.remove() method per-
forms delete operations.The db.collection.remove() method can accept a query criteria to determine which
documents to remove.
The following diagramhighlights the components of a MongoDB remove operation:
Figure 2.17:The components of a MongoDB remove operation.
The following diagramshows the same query in SQL:
Example
db.users.remove(
{ status:"D"}
)
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Figure 2.18:The components of a SQL DELETE statement.
This delete operation on the users collection removes all documents that match the criteria of status equal to D.
For more information,see db.collection.remove() method and Remove Documents (page 68).
Remove Behavior
By default,db.collection.remove() method removes all documents that match its query.However,the
method can accept a flag to limit the delete operation to a single document.
Isolation of Write Operations
The modification of a single document is always atomic,even if the write operation modifies multiple sub-documents