hash-field-expiry.md

Hash Field Expiry

Redis 7.4 introduced per-field expiration on hash keys. This allows you to set TTL on individual hash fields instead of the entire key.

Requires Redis 7.4+ and StackExchange.Redis 2.12+

Set a Field with Expiry

// Atomic set + expire in one command (HSETEX)
await redis.HashSetWithExpiryAsync("user:1", "session", sessionData, TimeSpan.FromMinutes(30));

// With absolute expiry
await redis.HashSetWithExpiryAsync("user:1", "token", tokenData, DateTime.UtcNow.AddHours(1));

Set Expiry on Existing Fields

// Set expiry on one or more fields (HEXPIRE)
var results = await redis.HashFieldExpireAsync("user:1",
    new[] { "session", "token" },
    TimeSpan.FromMinutes(15));

// Check results per field
foreach (var result in results)
    Console.WriteLine(result); // Success, FieldNotFound, etc.

Query Remaining TTL

// Get remaining TTL in milliseconds per field (HPTTL)
var ttls = await redis.HashFieldGetTimeToLiveAsync("user:1", new[] { "session", "name" });
// ttls[0] = 899542  (session: ~15 minutes remaining)
// ttls[1] = -1      (name: no expiry)

Remove Expiry

// Make fields permanent again (HPERSIST)
var results = await redis.HashFieldPersistAsync("user:1", new[] { "session" });

Use Case: User Sessions with Metadata

graph TB
    subgraph "Hash: user:1"
        name["name: 'Ugo'<br/><i>no expiry</i>"]
        email["email: 'ugo@example.com'<br/><i>no expiry</i>"]
        session["session: {data}<br/><i>TTL: 30 min</i>"]
        token["token: 'abc123'<br/><i>TTL: 1 hour</i>"]
    end

    style session fill:#FFE4B5
    style token fill:#FFE4B5

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This pattern stores permanent user data alongside ephemeral session data in the same hash, without needing separate keys.