The topic comes from Huawei's big data test. The following statement about Redis is true: ABCD. A. Redis mainly consumes physical memory resources. The tt 1 command in b. Redis is the remaining survival time of the view key. C. hash data type is suitable for storing objects in Redis. D, if you want to add 1 to the numeric value stored in the key, use the incr command.

1. Option A is correct. Redis is a key-value pair storage system based on memory, which mainly consumes physical memory resources. It stores data in memory, so it has high-speed reading and writing operations and low latency.

Option b is correct. In Redis, the TTL command is used to check the remaining life of the key, in seconds. This command can return the remaining lifetime of the key, or-1 if the key does not exist or the expiration time is not set.

3. Option C is correct. In Redis, the hash data type is suitable for storing objects. It is a collection of key-value pairs, which can be used to store data of multiple attributes. By using hash data types, we can store different attributes of an object in different key-value pairs, and we can access the whole object through a primary key.

4. Option D is correct. In Redis, the INCR command is used to add 1 to the numeric value stored in the specified key. If the key does not exist, set it to 1. If the key exists but the stored value is not a number, an error is returned. This command is usually used in scenarios such as counters and inventory management.

Redis application scenario:

1, session management: Redis can be used to store and manage user's session data. Because Redis has the characteristics of high-speed reading and writing and low latency, it can help the website to process user requests more quickly and maintain the persistence of the session.

2. Cache: Redis can cache the query results of the database into memory, thus speeding up the query speed of the database. This is very useful for frequently accessed data and can effectively reduce the load of the database.

3. Event queue: Redis can be used as an event queue. Producers send messages to queues, and consumers can get messages from queues and process them. Because of the atomic operation and high reliability of Redis, this application scenario is very suitable for asynchronous processing and distributed systems.

4. Leaderboards and counters: Redis can be used to realize functions such as leaderboards and counters. For example, the list data type of Redis can be used to store leaderboard data, and the atomic operation of Redis can be used to ensure the correctness of the data.

5. Distributed lock: Redis can be used as one of the implementations of distributed lock. Because Redis has the characteristics of high-speed reading and writing and atomic operation, it can effectively solve the concurrency problem in distributed systems.