Add docs for the DELIFEQ command

commands/delifeq.md

@@ -0,0 +1,58 @@
+Deletes the key if its value matches the given string.
+
+This command is typically used to safely release locks in distributed systems, ensuring that only the owner of the lock (as identified by the value) can delete it.
+
+If the key exists and the stored value is a string that exactly matches the provided value, the key is removed and `1` is returned. Otherwise, the key is left unchanged and `0` is returned.
+
+## Examples
+
+Basic usage:
+
+```
+127.0.0.1:6379> SET mykey abc123
+OK
+127.0.0.1:6379> DELIFEQ mykey abc123
+(integer) 1
+127.0.0.1:6379> DELIFEQ mykey abc123
+(integer) 0
+```
+
+Wrong value:
+
+```
+127.0.0.1:6379> SET mykey xyz789
+OK
+127.0.0.1:6379> DELIFEQ mykey abc123
+(integer) 0
+```
+
+Wrong type:
+
+```
+127.0.0.1:6379> SADD mykey somevalue
+(integer) 1
+127.0.0.1:6379> DELIFEQ mykey somevalue
+(error) WRONGTYPE Operation against a key holding the wrong kind of value
+```
+
+## Use case: Safe lock release
+
+`DELIFEQ` enables an atomic check-and-delete operation to safely release a lock only if the process still holds it. This avoids race conditions where a lock might expire and be claimed by another process before the original owner tries to delete it.
+
+This pattern is commonly used as part of distributed locking systems like [Redlock](../topics/distlock.md), which previously relied on Lua scripting to implement this logic. With `DELIFEQ`, such a use case becomes more robust and idiomatic.
+
+Instead of:
+
+```
+EVAL "if redis.call('GET',KEYS[1]) == ARGV[1] then return redis.call('DEL',KEYS[1]) else return 0 end" 1 mykey abc123
+```
+
+You can now use:
+
+```
+DELIFEQ mykey abc123
+```
+
+## See also
+
+* [`SET IFEQ`](set.md) - Sets the key only if it matches the given value.

commands/set.md

@@ -73,3 +73,7 @@ An example of unlock script would be similar to the following:
     end
 
 The script should be called with `EVAL ...script... 1 resource-name token-value`
+
+## See also
+
+* [`DELIFEQ`](delifeq.md) - Deletes the key if its value matches the given string.

resp2_replies.json

@@ -399,6 +399,11 @@
   "DEL": [
     "[Integer reply](../topics/protocol.md#integers): the number of keys that were removed."
   ],
+  "DELIFEQ": [
+    "One of the following:",
+    "* [Integer reply](../topics/protocol.md#integers): `1` if the key was deleted.",
+    "* [Integer reply](../topics/protocol.md#integers): `0` if the key was not deleted because it did not exist or the value was not equal to the provided value."
+  ],
   "DISCARD": [
     "[Simple string reply](../topics/protocol.md#simple-strings): `OK`."
   ],

resp3_replies.json

@@ -399,6 +399,11 @@
   "DEL": [
     "[Integer reply](../topics/protocol.md#integers): the number of keys that were removed."
   ],
+  "DELIFEQ": [
+    "One of the following:",
+    "* [Integer reply](../topics/protocol.md#integers): `1` if the key was deleted.",
+    "* [Integer reply](../topics/protocol.md#integers): `0` if the key was not deleted because it did not exist or the value was not equal to the provided value."
+  ],
   "DISCARD": [
     "[Simple string reply](../topics/protocol.md#simple-strings): `OK`."
   ],

topics/distlock.md

@@ -84,7 +84,13 @@ To acquire the lock, the way to go is the following:
 The command will set the key only if it does not already exist (`NX` option), with an expire of 30000 milliseconds (`PX` option).
 The key is set to a value “my\_random\_value”. This value must be unique across all clients and all lock requests.
 
-Basically the random value is used in order to release the lock in a safe way, with a script that tells Valkey: remove the key only if it exists and the value stored at the key is exactly the one I expect to be. This is accomplished by the following Lua script:
+Basically the random value is used in order to release the lock in a safe way, with a script that tells Valkey: remove the key only if it exists and the value stored at the key is exactly the one I expect to be.
+
+In Valkey 9.0.0 and later, this can be done atomically using the built-in DELIFEQ command:
+
+    DELIFEQ resource_name my_random_value
+
+In earlier versions of Valkey, the same behavior can be achieved using a Lua script:
 
     if server.call("get",KEYS[1]) == ARGV[1] then
         return server.call("del",KEYS[1])