How to Interpret "Evicted_keys" From Redis Info?

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The "evicted_keys" value in the output of the Redis INFO command represents the number of keys that have been evicted due to the maxmemory limit being reached. This typically occurs when Redis runs out of memory and needs to remove some keys to free up space for new data. Keeping an eye on the "evicted_keys" count can help monitor memory usage and performance of the Redis database.

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How to recover data from evicted keys in redis?

Unfortunately, once a key has been evicted in Redis, it is not possible to recover the data associated with that key. Redis uses a LRU (Least Recently Used) algorithm to evict keys when the memory limit is reached, and once a key has been evicted, the data is permanently lost.

To prevent data loss due to key eviction, you can consider increasing the memory limit of your Redis server, periodically backing up your data, or using a Redis persistence mechanism such as RDB snapshots or AOF logs to persist your data to disk. These measures can help prevent data loss and ensure that you have a backup in case of key eviction.

What role does evicted keys play in maintaining data consistency in redis?

Evicted keys in Redis play a role in maintaining data consistency by ensuring that the database does not become overwhelmed with too much data. When the maximum memory capacity for Redis is reached, the system will automatically evict keys to make room for new data, preventing data loss or crashing of the system.

By evicting keys based on certain eviction policies (such as LRU, LFU, or random eviction), Redis can effectively manage its memory usage and maintain data consistency by prioritizing the retention of more frequently accessed or recently added keys.

Overall, evicted keys help prevent memory congestion, ensure efficient data storage, and maintain a balanced performance in Redis.

How to detect and resolve evicted key conflicts in redis?

When a key is evicted from Redis due to memory constraints, a "keyspace-notification" event is generated. This event includes the name of the evicted key and the reason for eviction.

To detect and resolve evicted key conflicts in Redis, you can follow these steps:

  1. Monitoring: Set up monitoring tools like Redis MONITOR or Redis Sentinel to keep track of eviction events. You can also use external monitoring tools to monitor memory usage and key eviction rates.
  2. Logging: Enable Redis slow log and monitor the eviction logs. This can help you identify which keys are being evicted and track the reasons for eviction.
  3. Key TTL management: Set expiry times (TTL) for keys to prevent them from being evicted unintentionally. Make sure to set appropriate expiry times based on the importance of the key.
  4. Memory optimization: Optimize memory usage by removing unnecessary keys, using data structures efficiently, and enabling memory management features like eviction policies and maxmemory policy.
  5. Key conflict resolution: When conflicts arise due to evicted keys, consider using a hybrid storage solution where important keys are stored in Redis with persistence to disk, and less critical keys are stored in a secondary database. Implementing a backup and restore strategy can help recover evicted keys when needed.
  6. Capacity planning: Regularly monitor memory usage and plan for capacity upgrades or sharding if needed to accommodate growing data sets and reduce the likelihood of key conflicts.

By following these steps, you can effectively detect and resolve evicted key conflicts in Redis, ensuring data integrity and optimal performance.

How to monitor evicted_keys in real-time in redis?

One way to monitor evicted keys in real-time in Redis is by using Redis' built-in event notification system. Redis allows you to subscribe to specific events using the SUBSCRIBE command, including the evicted event which is triggered when a key is evicted from the cache.

To monitor evicted keys in real-time, you can use the following steps:

  1. Start a Redis client and subscribe to the evicted event:
SUBSCRIBE __keyspace@0__:evicted

  1. You will start receiving messages in real-time whenever a key is evicted from the Redis cache. You can process these messages as needed to monitor the evicted keys.

Alternatively, you can also set up a monitoring tool or script that periodically checks the INFO command output for the evicted_keys metric. This command provides information about the number of keys that have been evicted since the Redis server was started. You can parse this output and monitor the evicted keys count over time.

By using these methods, you can monitor evicted keys in real-time in Redis and take appropriate actions to manage the cache effectively.

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