Add performance warning to RedisOperations#keys() Javadoc.

Closes #3142
Signed-off-by: JavaNo0b <98101954+JavaNo0b@users.noreply.github.com>

Author: connorcoco

src/main/java/org/springframework/data/redis/core/RedisOperations.java

@@ -264,11 +264,14 @@ public interface RedisOperations<K, V> {
 	DataType type(@NonNull K key);
 
 	/**
-	 * Find all keys matching the given {@code pattern}.
-	 *
-	 * @param pattern must not be {@literal null}.
-	 * @return {@literal null} when used in pipeline / transaction.
-	 * @see <a href="https://redis.io/commands/keys">Redis Documentation: KEYS</a>
+	 * Retrieve keys matching the given pattern via {@code KEYS} command.
+	 * <p>
+	 * Note: This command scans the entire keyspace and may cause performance issues
+	 * in production environments. Prefer using {@link #scan(ScanOptions)} for large datasets.
+	 *
+	 * @param pattern key pattern
+	 * @return set of matching keys, or {@literal null} when used in pipeline / transaction
+	 * @see <a href="https://redis.io/commands/keys">Redis KEYS command</a>
 	 */
 	Set<@NonNull K> keys(@NonNull K pattern);