How do I delete everything in Redis?
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How to Delete Everything in Redis: A Comprehensive Guide
Learn the various methods to clear all data from your Redis instance, understand their implications, and choose the safest approach for your use case.
Deleting data in Redis is a common administrative task, whether for development, testing, or resetting a production instance. However, it's a powerful operation that, if misused, can lead to irreversible data loss. This article will guide you through the different commands available in Redis to delete all data, explain their nuances, and provide best practices to ensure you perform this critical operation safely and effectively.
Understanding FLUSHDB vs. FLUSHALL
Redis provides two primary commands for clearing data: FLUSHDB and FLUSHALL. While both achieve the goal of deleting data, they operate at different scopes. Understanding this distinction is crucial to avoid unintended data loss, especially in environments where multiple databases are in use.
FLUSHDB
Clears all keys from the currently selected database.
FLUSHALL
Clears all keys from all databases on the Redis server.
Scope of FLUSHDB vs. FLUSHALL
FLUSHALL, especially in production environments. It will wipe all data across all databases on your Redis server, impacting any applications sharing that instance.Asynchronous Deletion for Large Datasets
For Redis instances containing very large datasets, FLUSHDB and FLUSHALL can be blocking operations. This means the Redis server will pause all other operations until all keys are deleted, potentially causing application downtime. Redis 4.0 introduced asynchronous versions of these commands to address this issue, allowing the deletion to happen in the background without blocking the server.
FLUSHDB ASYNC
Initiates an asynchronous deletion of keys in the current database.
FLUSHALL ASYNC
Initiates an asynchronous deletion of keys across all databases.
ASYNC variants of FLUSHDB and FLUSHALL to prevent service interruptions.Deleting Specific Keys or Patterns
Sometimes, you don't need to delete everything, but rather a subset of keys matching a certain pattern. While not a 'delete everything' scenario, it's a related operation that administrators often need. Redis provides the DEL command for individual keys and, in conjunction with KEYS (which should be used with extreme caution in production), can target patterns.
DEL mykey
Deletes a single specified key.
DEL key1 key2 key3
Deletes multiple specified keys.
For deleting keys matching a pattern, you would typically combine KEYS with DEL in a script or application logic. However, KEYS is a blocking command and should be avoided in production environments for large datasets. A safer alternative is to use SCAN.