Time To Live

Objects stored in Redis may be valid only for a certain amount of time. This is especially useful for persisting short-lived objects in Redis without having to remove them manually when they reach their end of life. The expiration time in seconds can be set with @RedisHash(timeToLive=…) as well as by using KeyspaceConfiguration.KeyspaceSettings (see Keyspaces).

More flexible expiration times can be set by using the @TimeToLive annotation on either a numeric property or a method. However, do not apply @TimeToLive on both a method and a property within the same class. The following example shows the @TimeToLive annotation on a property and on a method:

Example 1. Expirations

public class TimeToLiveOnProperty {

  @Id
  private String id;

  @TimeToLive
  private Long expiration;
}

public class TimeToLiveOnMethod {

  @Id
  private String id;

  @TimeToLive
  public long getTimeToLive() {
  	return new Random().nextLong();
  }
}

Annotating a property explicitly with @TimeToLive reads back the actual TTL or PTTL value from Redis. -1 indicates that the object has no associated expiration.

The repository implementation ensures subscription to Redis keyspace notifications via RedisMessageListenerContainer.

When the expiration is set to a positive value, the corresponding EXPIRE command is run. In addition to persisting the original, a phantom copy is persisted in Redis and set to expire five minutes after the original one. This is done to enable the Repository support to publish RedisKeyExpiredEvent, holding the expired value in Spring’s ApplicationEventPublisher whenever a key expires, even though the original values have already been removed. Expiry events are received on all connected applications that use Spring Data Redis repositories.

By default, the key expiry listener is disabled when initializing the application. The startup mode can be adjusted in @EnableRedisRepositories or RedisKeyValueAdapter to start the listener with the application or upon the first insert of an entity with a TTL. See RedisKeyValueAdapter.EnableKeyspaceEvents for possible values.

The RedisKeyExpiredEvent holds a copy of the expired domain object as well as the key.

Delaying or disabling the expiry event listener startup impacts RedisKeyExpiredEvent publishing. A disabled event listener does not publish expiry events. A delayed startup can cause loss of events because of the delayed listener initialization.

The keyspace notification message listener alters notify-keyspace-events settings in Redis, if those are not already set. Existing settings are not overridden, so you must set up those settings correctly (or leave them empty). Note that CONFIG is disabled on AWS ElastiCache, and enabling the listener leads to an error. To work around this behavior, set the keyspaceNotificationsConfigParameter parameter to an empty string. This prevents CONFIG command usage.

Redis Pub/Sub messages are not persistent. If a key expires while the application is down, the expiry event is not processed, which may lead to secondary indexes containing references to the expired object.

@EnableKeyspaceEvents(shadowCopy = OFF) disable storage of phantom copies and reduces data size within Redis. RedisKeyExpiredEvent will only contain the id of the expired key.