Managing Redis from the console · Redis Basics

How to delete keys and flush the cache in Redis

Delete Redis keys with DEL and UNLINK, remove many by pattern, and delete all keys with FLUSHDB vs FLUSHALL. Plus the danger of flushing production.

How to delete keys in Redis

You can find keys and inspect them. Removing them is the next step, and the question splits three ways: how do I delete one key, a batch that share a pattern, or delete all keys in Redis at once? Each has a right tool. The whole-cache ones are the most dangerous commands in this course, so we save them for last and handle them carefully.

DEL: delete one or more keys

DEL removes keys and returns how many it actually deleted:

127.0.0.1:6379> DEL user:42:name
(integer) 1

You can pass several at once:

127.0.0.1:6379> DEL user:42:name user:42:email session:abc
(integer) 3

A return of 0 just means none of those keys existed. DEL never errors on a missing key.

UNLINK: delete without blocking

DEL frees the memory immediately, before returning. For a huge value (a list with millions of items), that freeing can briefly block the server, the same single-threaded problem you saw with KEYS.

UNLINK avoids it. It removes the key from the keyspace right away, then frees the memory in the background:

127.0.0.1:6379> UNLINK big:list
(integer) 1

From your point of view the key is gone instantly. Rule of thumb: for big values, or when in doubt on production, prefer UNLINK. For a handful of small keys, DEL is perfectly fine.

Deleting many keys by pattern

Redis has no "delete by pattern" command, on purpose, since that would be a blocking scan. Instead you combine the safe --scan from the previous lesson with xargs:

redis-cli --scan --pattern 'cache:*' | xargs redis-cli DEL

Read it left to right: --scan lists every matching key one per line, and xargs feeds those keys as arguments to redis-cli DEL. Both halves use SCAN under the hood, so this stays safe even on a large database.

Before you delete, run the left half alone to see exactly what will go:

redis-cli --scan --pattern 'cache:*'

Look at the list first, then add the | xargs redis-cli DEL. This one habit prevents most accidents.

Delete all keys: FLUSHDB vs FLUSHALL

Sometimes you want everything gone. Two commands do it, and the difference matters.

FLUSHDB empties the current database only:

127.0.0.1:6379> FLUSHDB
OK

FLUSHALL empties every database on the server, all sixteen:

127.0.0.1:6379> FLUSHALL
OK

Both accept ASYNC, which frees the memory in the background so the command returns instantly, the flush version of UNLINK:

127.0.0.1:6379> FLUSHDB ASYNC
OK

Common mistake

This is the one that ends careers. FLUSHALL and FLUSHDB delete data instantly, with no confirmation and no undo. Two ways people get burned:

  • Running FLUSHALL on production, thinking it was staging. Every cache, session, and queue vanishes at once.
  • Being on the wrong database. You SELECTed the wrong number earlier, run FLUSHDB expecting to clear a test database, and wipe the live one.

Protect yourself: before any flush, check the prompt to confirm the host and the [n] database number, and prefer a targeted --scan | xargs DEL over a flush whenever you can. If you only need to remove some keys, never reach for FLUSHALL.

This is common enough that many production setups disarm the command entirely. Using rename-command FLUSHALL "" in the config, an ops team can leave FLUSHALL doing nothing at all, so a stray flush cannot wipe the server even if someone types it. If a flush ever comes back with "unknown command" on a real box, that is not a bug, it is a seatbelt someone fastened on purpose.

FAQ

How do I delete all keys in Redis?

FLUSHDB clears the database you are currently on; FLUSHALL clears every database on the server. Both are instant and cannot be undone, so confirm the host and database first.

What is the difference between DEL and UNLINK?

DEL frees the memory before it returns, which can briefly block on very large values. UNLINK removes the key immediately and frees the memory in the background, so it never blocks.

How do I delete keys by pattern in Redis?

There is no built-in pattern delete. Combine the safe scan with xargs: redis-cli --scan --pattern 'x:*' | xargs redis-cli DEL. Run the scan alone first to preview what will be removed.

What is the difference between FLUSHDB and FLUSHALL?

FLUSHDB empties only the current database. FLUSHALL empties all sixteen databases on the server. Add ASYNC to free the memory in the background.