Glossary: Etags

What are Etags?

RavenDB uses etags to track changes of data. Etags are 64-bit numbers which always increase with each change. If comparing etags for two versions of the same document on a specific RavenDB instance, the version with a higher etag is more up-to-date.

Etags vs. Change Vectors

Both etags and change vectors are used to track document changes. Etags have meaning local to cluster nodes, and change vectors have meaning cluster-wide.

• An etag is only incremented when a document is modified locally
• Change Vector may be changed when a document is modified locally or replicated

Etags In-Depth

In RavenDB, etags track changes on many different types of server entities.

Etags are used to track changes to the following:

• Documents
• Indexes
• Cluster Topology
• ETL

For developing with the RavenDB client API, etags are not needed. Etags are used as a "building block" of a Change Vector.

Etags and Clustering

When looking at etags in the context of a RavenDB cluster, etags are only meaningful within a single database on a specific node. This means etags are not universally unique per different databases on a single node and are not unique across cluster nodes.