Table of Contents

StackExchange.Redis

OptunaSharp.Storage.StackExchange.Redis provides StackExchangeJournalRedisBackend in OptunaSharp.Storages.Journal. It uses StackExchange.Redis IDatabase string commands and Lua execution to implement the shared Redis journal format.

Install and use

Requires .NET 8 or .NET 10 and a reachable Redis server.

dotnet add package OptunaSharp.Storage.StackExchange.Redis

using OptunaSharp;
using OptunaSharp.Storages.Journal;
using StackExchange.Redis;

using var connection = ConnectionMultiplexer.Connect(new ConfigurationOptions
{
    EndPoints = { "localhost:6379" },
    ConnectTimeout = 5000,
    SyncTimeout = 5000,
    ClientName = "optunasharp-worker",
});

var backend = new StackExchangeJournalRedisBackend(connection, prefix: "experiments");
var study = Optuna.CreateStudy(
    storage: new JournalStorage(backend),
    studyName: "quadratic", loadIfExists: true);
study.Optimize(trial => Math.Pow(trial.SuggestFloat("x", -10, 10), 2), nTrials: 20);

The multiplexer is application-owned. Keep it alive for all workers that use it, and dispose it after their work finishes. Disposing the backend leaves an injected multiplexer open. A backend built from a URL or ConfigurationOptions owns its multiplexer instead, and Dispose() closes it.

Constructors and database selection

First arguments Behavior
string url Parse redis://, rediss://, or unix://, then create a multiplexer
string url, Action<ConfigurationOptions> configure Parse URL, apply callback, then connect
ConfigurationOptions options Connect using the supplied native options
IConnectionMultiplexer connection Borrow an existing connection

All overloads also take bool useCluster = false, string prefix = "". URL database selection sets ConfigurationOptions.DefaultDatabase; an injected connection uses its configured default database because the backend calls GetDatabase() without a database argument.

The URL path sets AbortOnConnectFail = false before invoking any callback. This permits constructing the connection while the server is unavailable, but the subsequent journal load or write still needs a working Redis connection. The native-options and injected-client paths preserve the configuration you supplied.

A URL callback can configure client timeouts or naming:

using OptunaSharp.Storages.Journal;

var backend = new StackExchangeJournalRedisBackend(
    "redis://localhost:6379/1",
    options =>
    {
        options.ConnectTimeout = 5000;
        options.SyncTimeout = 5000;
        options.ClientName = "optunasharp-worker";
    },
    prefix: "experiments");

This convenience form creates an internal multiplexer. Use the injected-client form from the first example for deterministic shutdown. Native options expose TLS configuration, endpoint lists, and the other StackExchange.Redis connection settings; they do not alter the journal data model.

Behavior and limits

On standalone Redis, ReadLogs and the append both go through ScriptEvaluate: one read-only script call per batch of up to 1,000 records, and one append script call per record, which seeds the counter itself. Cluster mode reads with StringGet, seeds the counter with StringSet(..., When.NotExists) and appends with StringIncrement followed by StringSet. Snapshots use raw Redis byte values under {prefix}:snapshot:optunasharp. The URL and options constructors turn on StackExchange.Redis's DedicatedThreads flag before connecting unless you pass dedicatedThreads: false; the Redis overview explains why, and what that flag affects.

Read the Redis overview for prefix isolation, non-atomic cluster writes, missing-record waits, and runtime-specific snapshots. NRedisStack and ServiceStack.Redis can access the same logs when pointed at the same database and prefix.

Implementation: StackExchangeJournalRedisBackend. Verification covers all constructor forms, cross-library bytes, and Python read/write interoperability.

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