Document history

Since – by default – ShareDB stores all of the submitted operations, these operations can be used to reconstruct a document at any point in its history.

ShareDB exposes two methods for this:

• connection.fetchSnapshot() – fetches a snapshot by version number
• connection.fetchSnapshotByTimestamp() – fetches a snapshot by UNIX timestamp

ShareDB doesn’t support “branching” a document. Any historical snapshots fetched will be read-only.

Milestone snapshots

Since OT types are only optionally reversible, ShareDB rebuilds its historic snapshots by replaying ops all the way from creation to the requested version.

Once documents reach a high version, rebuilding a document like this can get slow. In order to facilitate this, ShareDB supports Milestone Snapshots – snapshots that are periodically saved, so that ShareDB can jump to the nearest snapshot, and rebuild from there.

In order to benefit from this performance improvement, a milestone adapter should be configured.