Managing Databases

1. Selecting Database

Command	Description
`SELECT index`	Switch current connection to DB index (0..15 default)
`redis-cli -n 3`	Connect directly to DB 3

Command	Returns
`DBSIZE`	Number of keys in current DB
`INFO keyspace`	Per-DB key/expire/avg-ttl stats

Command	Effect
`FLUSHDB`	Delete all keys in current DB (sync)
`FLUSHDB ASYNC`	Delete in background, non-blocking
`FLUSHDB SYNC`	Force synchronous flush

FLUSHALL          # all DBs, sync
FLUSHALL ASYNC    # all DBs, background
FLUSHALL SYNC     # force blocking

Warning: Disable in production via rename-command FLUSHALL "".

Command	Behavior
`MOVE key db`	Atomic move; fails if key exists in target
`COPY src dst DB n REPLACE`	Copy across DBs, optionally overwrite 6.2+

Command	Effect
`SWAPDB a b`	Atomically swap two DB indexes; instant cutover for blue/green data

SELECT 1
# load fresh data into DB 1 ...
SWAPDB 0 1      # production reads now hit fresh dataset
FLUSHDB ASYNC   # clean up old data

Variant	Behavior
`FLUSHDB ASYNC`	Reclaim memory in background thread
`UNLINK key ...`	Non-blocking key delete (preferred over `DEL` for large values)
`lazyfree-lazy-user-flush`	Config to make FLUSH commands async by default

Setting	Notes
`databases 16`	Default; raise to use more logical DBs
Cluster mode	Only DB 0 is allowed