Snapshots

Snapshots are online point-in-time backups. The database remains fully operational during a snapshot, and db.Snapshot() performs an immediate flush before reading the data files — every write up to the snapshot call is included.

A snapshot contains only the fresh (current) version of each record. Stale and deleted history present in the source .db/.map files is not carried over. As a result, a snapshot is effectively a defragged copy of the live dataset — typically smaller than the source when the source has accumulated stale records.

Snapshot files are named htl.{yyyyMMdd.HHmm.ss.fff}.{datasetName}.db and .map. A snapshot is a fully independent database, openable in any mode, and requires the same configuration as the source (serializer, encryption key, and any other settings must match).

Snapshots are not compatible with ReadOnly access mode — configuring SnapshotTo on a ReadOnly database throws at configuration time. Snapshots are taken from the persisted files, not the in-memory cache; that is why an immediate flush precedes every snapshot.

// 1. Configure a snapshot destination
MemDb.ConfigureFor<Person>("people", _dbDirectory)
    .SerializeWith(() => new PersonSerializer())
    .EncryptWithPassword(() => "SuperSecureEncryptionPasswordGoesHere.")
    .SnapshotTo(Path.Combine(_dbDirectory, "snapshots"))
    .Register();

// 2. Take a snapshot — returns the timestamp of the snapshot
DateTime snappedAt;
using (var db = MemDb.Open<Person>("people"))
{
    // ... operations ...
    snappedAt = db.Snapshot();

    // changes made after this point will NOT be in the snapshot
}

// 3. Open the snapshot
string snapshotDatasetName = MemDb.GetConfiguration("people").GetSnapshotDatasetName(snappedAt);
MemDb.ConfigureFor<Person>(snapshotDatasetName, Path.Combine(_dbDirectory, "snapshots"))
    .SerializeWith(() => new PersonSerializer())
    .EncryptWithPassword(() => "SuperSecureEncryptionPasswordGoesHere.")
    .Register();

using (var snap = MemDb.Open<Person>(snapshotDatasetName))
{
    // snapshot reflects the state of the database at the time db.Snapshot() was called
}

Maintenance Extensibility