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MongoDB: The Definitive Guide

Cover of MongoDB: The Definitive Guide by Michael Dirolf... Published by O'Reilly Media, Inc.
  1. MongoDB: The Definitive Guide
  2. Foreword
  3. Preface
    1. How This Book Is Organized
      1. Getting Up to Speed with MongoDB
      2. Developing with MongoDB
      3. Advanced Usage
      4. Administration
      5. Developing Applications with MongoDB
      6. Appendixes
    2. Conventions Used in This Book
    3. Using Code Examples
    4. Safari® Books Online
    5. How to Contact Us
    6. Acknowledgments
      1. Acknowledgments from Kristina
      2. Acknowledgments from Michael
  4. 1. Introduction
    1. A Rich Data Model
    2. Easy Scaling
    3. Tons of Features…
    4. …Without Sacrificing Speed
    5. Simple Administration
    6. But Wait, That’s Not All…
  5. 2. Getting Started
    1. Documents
    2. Collections
      1. Schema-Free
      2. Naming
    3. Databases
    4. Getting and Starting MongoDB
    5. MongoDB Shell
      1. Running the Shell
      2. A MongoDB Client
      3. Basic Operations with the Shell
      4. Tips for Using the Shell
    6. Data Types
      1. Basic Data Types
      2. Numbers
      3. Dates
      4. Arrays
      5. Embedded Documents
      6. _id and ObjectIds
  6. 3. Creating, Updating, and Deleting Documents
    1. Inserting and Saving Documents
      1. Batch Insert
      2. Inserts: Internals and Implications
    2. Removing Documents
      1. Remove Speed
    3. Updating Documents
      1. Document Replacement
      2. Using Modifiers
      3. Upserts
      4. Updating Multiple Documents
      5. Returning Updated Documents
    4. The Fastest Write This Side of Mississippi
      1. Safe Operations
      2. Catching “Normal” Errors
    5. Requests and Connections
  7. 4. Querying
    1. Introduction to find
      1. Specifying Which Keys to Return
      2. Limitations
    2. Query Criteria
      1. Query Conditionals
      2. OR Queries
      3. $not
      4. Rules for Conditionals
    3. Type-Specific Queries
      1. null
      2. Regular Expressions
      3. Querying Arrays
      4. Querying on Embedded Documents
    4. $where Queries
    5. Cursors
      1. Limits, Skips, and Sorts
      2. Avoiding Large Skips
      3. Advanced Query Options
      4. Getting Consistent Results
    6. Cursor Internals
  8. 5. Indexing
    1. Introduction to Indexing
      1. Scaling Indexes
      2. Indexing Keys in Embedded Documents
      3. Indexing for Sorts
      4. Uniquely Identifying Indexes
    2. Unique Indexes
      1. Dropping Duplicates
      2. Compound Unique Indexes
    3. Using explain and hint
    4. Index Administration
      1. Changing Indexes
    5. Geospatial Indexing
      1. Compound Geospatial Indexes
      2. The Earth Is Not a 2D Plane
  9. 6. Aggregation
    1. count
    2. distinct
    3. group
      1. Using a Finalizer
      2. Using a Function as a Key
    4. MapReduce
      1. Example 1: Finding All Keys in a Collection
      2. Example 2: Categorizing Web Pages
      3. MongoDB and MapReduce
  10. 7. Advanced Topics
    1. Database Commands
      1. How Commands Work
      2. Command Reference
    2. Capped Collections
      1. Properties and Use Cases
      2. Creating Capped Collections
      3. Sorting Au Naturel
      4. Tailable Cursors
    3. GridFS: Storing Files
      1. Getting Started with GridFS: mongofiles
      2. Working with GridFS from the MongoDB Drivers
      3. Under the Hood
    4. Server-Side Scripting
      1. db.eval
      2. Stored JavaScript
      3. Security
    5. Database References
      1. What Is a DBRef?
      2. Example Schema
      3. Driver Support for DBRefs
      4. When Should DBRefs Be Used?
  11. 8. Administration
    1. Starting and Stopping MongoDB
      1. Starting from the Command Line
      2. File-Based Configuration
      3. Stopping MongoDB
    2. Monitoring
      1. Using the Admin Interface
      2. serverStatus
      3. mongostat
      4. Third-Party Plug-Ins
    3. Security and Authentication
      1. Authentication Basics
      2. How Authentication Works
      3. Other Security Considerations
    4. Backup and Repair
      1. Data File Backup
      2. mongodump and mongorestore
      3. fsync and Lock
      4. Slave Backups
      5. Repair
  12. 9. Replication
    1. Master-Slave Replication
      1. Options
      2. Adding and Removing Sources
    2. Replica Sets
      1. Initializing a Set
      2. Nodes in a Replica Set
      3. Failover and Primary Election
    3. Performing Operations on a Slave
      1. Read Scaling
      2. Using Slaves for Data Processing
    4. How It Works
      1. The Oplog
      2. Syncing
      3. Replication State and the Local Database
      4. Blocking for Replication
    5. Administration
      1. Diagnostics
      2. Changing the Oplog Size
      3. Replication with Authentication
  13. 10. Sharding
    1. Introduction to Sharding
    2. Autosharding in MongoDB
      1. When to Shard
    3. The Key to Sharding: Shard Keys
      1. Sharding an Existing Collection
      2. Incrementing Shard Keys Versus Random Shard Keys
      3. How Shard Keys Affect Operations
    4. Setting Up Sharding
      1. Starting the Servers
      2. Sharding Data
    5. Production Configuration
      1. A Robust Config
      2. Many mongos
      3. A Sturdy Shard
      4. Physical Servers
    6. Sharding Administration
      1. config Collections
      2. Sharding Commands
  14. 11. Example Applications
    1. Chemical Search Engine: Java
      1. Installing the Java Driver
      2. Using the Java Driver
      3. Schema Design
      4. Writing This in Java
      5. Issues
    2. News Aggregator: PHP
      1. Installing the PHP Driver
      2. Using the PHP Driver
      3. Designing the News Aggregator
      4. Trees of Comments
      5. Voting
    3. Custom Submission Forms: Ruby
      1. Installing the Ruby Driver
      2. Using the Ruby Driver
      3. Custom Form Submission
      4. Ruby Object Mappers and Using MongoDB with Rails
    4. Real-Time Analytics: Python
      1. Installing PyMongo
      2. Using PyMongo
      3. MongoDB for Real-Time Analytics
      4. Schema
      5. Handling a Request
      6. Using Analytics Data
      7. Other Considerations
  15. A. Installing MongoDB
    1. Choosing a Version
    2. Windows Install
      1. Installing as a Service
    3. POSIX (Linux, Mac OS X, and Solaris) Install
      1. Installing from a Package Manager
  16. B. mongo: The Shell
    1. Shell Utilities
  17. C. MongoDB Internals
    1. BSON
    2. Wire Protocol
    3. Data Files
    4. Namespaces and Extents
    5. Memory-Mapped Storage Engine
  18. Index
  19. About the Authors
  20. Colophon
  21. Copyright
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Chapter 9. Replication

Perhaps the most important job of any MongoDB administrator is making sure that replication is set up and functioning correctly. Use of MongoDB’s replication functionality is always recommended in production settings, especially since the current storage engine does not provide single-server durability (see Appendix C for details). Replicas can be used purely for failover and data integrity, or they can be used in more advanced ways, such as for scaling out reads, taking hot backups, or as a data source for offline batch processing. In this chapter, we’ll cover everything you need to know about replication.

Master-Slave Replication

Master-slave replication is the most general replication mode supported by MongoDB. This mode is very flexible and can be used for backup, failover, read scaling, and more (see Figures 9-1 and 9-2).

A master with one slave

Figure 9-1. A master with one slave

The basic setup is to start a master node and one or more slave nodes, each of which knows the address of the master. To start the master, run mongod --master. To start a slave, run mongod --slave --source master_address, where master_address is the address of the master node that was just started.

It is simple to try this on a single machine, although in production you would use multiple servers. First, create a directory for the master to store data in and choose a port (10000):

$ mkdir -p ~/dbs/master $ ...

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