CouchDB: The Definitive Guide

Chapter 16. Replication

This chapter introduces CouchDB’s world-class replication system. Replication synchronizes two copies of the same database, allowing users to have low latency access data no matter where they are. These databases can live on the same server or on two different servers—CouchDB doesn’t make a distinction. If you change one copy of the database, replication will send these changes to the other copy.

Replication is a one-off operation: you send an HTTP request to CouchDB that includes a source and a target database, and CouchDB will send the changes from the source to the target. That is all. Granted, calling something world-class and then only needing one sentence to explain it does seem odd. But part of the reason why CouchDB’s replication is so powerful lies in its simplicity.

Let’s see what replication looks like:

POST /_replicate HTTP/1.1
{"source":"database","target":"http://example.org/database"}

This call sends all the documents in the local database database to the remote database http://example.org/database. A database is considered “local” when it is on the same CouchDB instance you send the POST /_replicate HTTP request to. All other instances of CouchDB are “remote.”

If you want to send changes from the target to the source database, you just make the same HTTP requests, only with source and target database swapped. That is all.

POST /_replicate HTTP/1.1
{"source":"http://example.org/database","target":"database"}

A remote database is identified by the ...