What is Document Versioning?

Document versioning refers to the practice of tracking and managing multiple versions of a document over time. In many applications, document changes need to be recorded rather than overwritten, ensuring historical integrity and compliance with regulations. Versioning is critical in industries such as finance, healthcare, legal, and content management, where keeping an accurate record of past document states is essential for audits, accountability, and compliance.

How Versioning Works in Different Systems

In traditional databases and content management systems, versioning is often handled using:

• Row-based historical tracking (e.g., a database table storing each document version with timestamps and unique identifiers).
• Event sourcing (capturing all changes as immutable events in an append-only log).
• Snapshot and delta storage (storing periodic full copies and incremental changes between versions).
  However, in OpenSearch, snapshots are scheduled at fixed intervals rather than triggered by document changes, meaning they may not always capture the latest updates in real-time.

OpenSearch: A Search Layer, Not a Versioning System

OpenSearch is a powerful distributed search and analytics engine, but it is not designed for document version control. While it provides a built-in _version field, this feature is primarily intended for optimistic concurrency control—not for maintaining historical versions of documents. If you update a document in OpenSearch, the _version number increments, but the previous state is lost. There is no native mechanism to retrieve past versions of a document.

This means that applications requiring audit trails, compliance tracking, or historical data retrieval need a custom approach to versioning. OpenSearch is optimized for search and retrieval speed, not for serving as an authoritative data store. The best practice is to treat OpenSearch as a search layer while keeping the true source of data (including historical versions) in a separate, persistent database.

Why OpenSearch is Not Optimized for Versioning

Unlike traditional databases, OpenSearch follows a distributed architecture that makes version tracking challenging:

1. Eventual Consistency: Updates are indexed asynchronously, meaning that documents may not appear updated in search results immediately.
2. Sharding Complexity: Data is split across multiple shards, making atomic updates and transactions difficult to implement at scale.
3. Optimized for Read Performance: OpenSearch is built for fast, scalable search operations, not transactional integrity.
4. No Native Version History: The _version field only tracks the latest version, with no capability to retrieve past document states.

For example, if an application tracks legal contracts or medical records, simply relying on OpenSearch’s _version field would not provide a verifiable audit history—previous versions would be irreversibly lost.

Using the Cloud for Compliance and Versioning

For organizations that need regulatory compliance, security, and versioning best practices, leveraging cloud services is the most effective approach. Cloud providers like AWS offer managed solutions that help achieve compliance while maintaining performance and scalability.

AWS Solutions for Versioning and Compliance

Amazon Web Services (AWS) provides several services that facilitate document versioning, retention, and compliance in cloud environments:

1. Amazon S3 with Versioning
   • Stores every version of a document, ensuring that no data is lost.
   • Provides lifecycle policies to automatically manage older versions.
   • Integrates with AWS Backup for long-term archival.
2. Amazon DynamoDB for Immutable Data Storage
   • Supports time-stamped records to track all changes.
   • Ensures strong consistency while keeping historical data.
   • Works well with OpenSearch as a backend for storing authoritative document history.
3. AWS Backup and AWS Audit Manager
   • Automates backups across AWS services, ensuring retention of historical records.
   • Helps meet compliance requirements for regulations like GDPR, HIPAA, and SOC 2.
4. Amazon OpenSearch Service with Fine-Grained Access Control
   • Integrates with AWS IAM to enforce security policies.
   • Provides detailed audit logging through AWS CloudTrail.
   • Ensures encrypted storage and secure data access.
5. AWS Managed Blockchain for Tamper-Proof Versioning
   • Provides an immutable ledger for tracking document changes.
   • Can be integrated with OpenSearch for fast retrieval.

By combining OpenSearch with AWS’s managed storage, security, and compliance services, organizations can ensure that document versioning is handled securely, efficiently, and in accordance with industry regulations.

Understanding OpenSearch’s _version Field

While OpenSearch assigns each document a _version, this does not function like traditional version control systems such as Git or database transaction logs. Instead, _version is used to prevent conflicts when multiple clients attempt to update the same document.

How _version Works

1. A document is indexed for the first time → _version = 1
2. A client updates the document → _version increments (_version = 2)
3. Another update occurs → _version = 3
4. However, previous versions are overwritten, not stored.

If two clients try to update the same document simultaneously, OpenSearch can reject changes that do not match the expected _version. This ensures concurrent updates do not overwrite each other, but it does not provide a way to retrieve historical versions.

Example: Updating a Document

# Add a document

PUT /my_index/_doc/1
{
  "title": "First Version",
  "content": "This is the first version of the document."
}

# Update a document

PUT /my_index/_doc/1
{
  "title": "Updated Version",
  "content": "This is the updated version of the document."
}

After the second PUT request, the original version is completely replaced. The _version number increases, but the old data is lost.

What happens if you try to retrieve version 1? Unlike databases that store historical states, OpenSearch only retains the latest version. Querying for an old version (e.g., GET /my_index/_doc/1?version=1) will not work—only the most recent document is available.

Conclusion: Key Takeaways

In this article, we explored the challenges and solutions for document versioning in OpenSearch. Key takeaways include:

• OpenSearch is not a versioning system; it is optimized for search, not for maintaining historical records.
• The built-in _version field is only for optimistic concurrency control and does not store historical versions.
• Applications requiring audit trails, compliance, and historical tracking should maintain a separate source of truth, such as a database or object storage.
• AWS provides robust tools for compliance, including Amazon S3 with versioning, DynamoDB, OpenSearch Service with IAM control, and AWS Backup.
• The best strategy for OpenSearch versioning depends on the use case and can include flag-based indexing, parent-child relationships, aggregations, or hybrid approaches.

With this foundation, we are now ready to explore specific strategies for managing document versions in OpenSearch. Stay tuned for the next article:

“Document Versioning in OpenSearch: Using a Database as the Source of Truth: Best Practices for OpenSearch Integration.”