Interface IJournalSnapshotInterval

Namespace

OptunaSharp.Storages.Journal

Assembly

OptunaSharp.dll

A snapshot-capable journal backend that tells JournalStorage how many study or trial ids apart to save a replay snapshot when the caller does not choose. OptunaSharp only: Optuna snapshots every 100 ids whatever the backend, and has no such interface.

public interface IJournalSnapshotInterval

Remarks

A snapshot pays off when replaying the records it replaces costs more than restoring it, and it costs the worker that saves it a serialization of the whole study, under the storage's lock. Which side wins depends on how the backend reads its records, which only the backend knows. Measured on 2026-11-07 at 20,000 trials on a Redis journal (Release build, with the binary snapshot of plan 10, item 2.7): reading the records in batches, a cold start took 927 ms without any snapshot, 170 ms with one every 1000 ids and 109 ms with one every 100; reading one record per round trip (cluster mode), 70.8 s, 3.3 s and 0.43 s. Saving a snapshot of that study takes about 20 ms, so the Redis backends answer Optuna's 100 in both modes (the owner's choice; a standalone server used 1000 until then).

JournalStorage reads DefaultSnapshotInterval once, in its constructor, and only when that constructor's snapshotInterval argument is null. A backend that stores snapshots (IBaseJournalSnapshot) without implementing this interface gets Optuna's 100. Implementing it on a backend without snapshots changes nothing.

Properties

DefaultSnapshotInterval

How many study or trial ids apart a JournalStorage over this backend saves a snapshot when its constructor is not given one: the worker that creates a study or trial whose id is a multiple of this value saves the whole replay state. Must be at least 1.

int DefaultSnapshotInterval { get; }

Property Value

int

Remarks

A value below 1 makes the JournalStorage constructor throw ArgumentException rather than snapshot on every id (1) or never; a backend that should never snapshot should not implement IBaseJournalSnapshot.