Configuring Replication in CouchDB

Replication in CouchDB allows you to synchronize data between databases, enabling data redundancy, distribution, and backup. This tutorial will guide you through the steps to configure replication in CouchDB and provide examples of commands and code.

1. Setting up Replication

To configure replication, follow these steps:

1. Create a new database or identify the target database for replication.
2. Choose the replication method:
• One-Time Replication: Use the curl command or CouchDB's HTTP API to initiate a one-time replication. For example:

$ curl -X POST http://localhost:5984/_replicate -d '{


"source": "http://source-db:5984/mydb",
"target": "http://localhost:5984/mydb",
"create_target": true
}'

• Continuous Replication: Create a replication document to enable continuous replication. This document specifies the source and target databases and other replication settings. For example:

{


"_id": "myreplication",
"source": "http://source-db:5984/mydb",
"target": "http://localhost:5984/mydb",
"continuous": true
}

Save this document to a new database or update an existing database.

Common Mistakes:

• Incorrectly specifying the source or target URL.
• Failure to enable continuous replication when needed.
• Insufficient permissions to access the source or target databases.

Frequently Asked Questions (FAQs):

1. Can I replicate data between CouchDB instances on different servers?

   Yes, you can replicate data between CouchDB instances running on different servers. Ensure that the appropriate network connectivity and access permissions are in place.

2. How do I monitor the replication process?

   CouchDB provides a _active_tasks endpoint that shows the status of active replications. You can query this endpoint to monitor the progress of ongoing replications.

3. What happens if there are conflicts during replication?

   In the event of conflicts, CouchDB uses a conflict resolution algorithm based on document revision numbers. You can define custom conflict resolution functions or let CouchDB choose the winning revision automatically.

4. Can I filter the data being replicated?

   Yes, you can use replication filters to specify which documents to include or exclude during replication. Filters are defined in the replication document using a JavaScript function.

5. Is it possible to replicate only specific document types or subsets of data?

   Yes, you can use filters to replicate only specific document types or subsets of data based on custom criteria.

Summary:

Configuring replication in CouchDB enables you to synchronize data between databases efficiently. Whether you need one-time or continuous replication, following the steps outlined in this tutorial will help you set up replication successfully. Be mindful of common mistakes and refer to the FAQs for additional guidance. Replication is a powerful feature that ensures data availability and redundancy in CouchDB.