redis learns master-slave replication Master/slave

LINDEX is a command in Redis to get the element of the specified index position in a list. Its syntax is LINDEXkeyindex, which supports positive and negative indexes. Positive numbers start from the head, 0 represents the first element; negative numbers are counted from the tail, and -1 is the last element. This command is suitable for scenes where you only need to get a single element and is more efficient than LRANGE. Pay attention to when using: 1. Make sure that the index is within the list length range, otherwise nil will be returned; 2. The list length can be obtained through LLEN to verify the index legitimacy; 3. Support negative indexes to facilitate access to the end elements; 4. Avoid frequent use of large lists, because their time complexity is O(N) may affect performance.

Ifamessageispublishedtoatopicorchannelwithnosubscribers,ittypicallygetslostunlessspecificmechanismsareinplace.1.InRabbitMQ,messagesmaystayinaqueueuntilaconsumerconnectsifnoconsumerisbound.2.InPub/SubsystemslikeGoogleCloudPub/Sub,messagesareusuallydis

1. The memory database stores data in RAM, which is suitable for scenarios that require ultra-low latency, but is easily lost after power failure; 2. The disk database stores data on a hard disk or SSD, which has data durability and is suitable for applications that cannot tolerate data loss; 3. The memory database is fast and suitable for real-time analysis, high-frequency trading and other scenarios, while the disk database is suitable for large-scale data and long-term storage; 4. The memory database requires additional measures to ensure durability, and the cost is high. Choice should be determined based on speed, reliability and cost requirements.

LRANGE is used to take out elements of the specified range from the Redis list, supporting positive and negative indexes; 1. Use 0 to -1 for the entire list; 2. Use 0 to N-1 for the first N; 3. Use -N to -1 for the last N; 4. Use -N to -1 for the page; 4. Use paging to control by start and stop; note that starting is greater than the length or stop exceeds the end, will return empty or valid part, and start>stop also returns empty, which is suitable for cache, log, queue and other scenarios.

Redisslowlog is a log system that records commands that take too long to execute, and is used to identify performance issues. 1. It records each command that exceeds the specified execution time, including log ID, timestamp, execution time, commands and parameters; 2. Use redis-clislowlogget to view the log, and the 10 slowest commands are returned by default, and the number can be specified by parameters; 3. Use slowlog-log-slower-than to configure the threshold, which is 10 milliseconds by default, -1 means recording all commands, and 0 means disable; 4. The maximum number of log entries is controlled by slowlog-max-len, and the default is 128, which can be adjusted but will occupy memory; 5. It is often used to troubleshoot slowdowns in applications, impacts and characteristics of new functions.

Redis's MSET command allows multiple key-value pairs to be set in one operation. The basic syntax is MSETkey1value1key2value2...keyNvalueN, for example, MSETusernamejohn_doeemailjohn@example.comstatusactive can store multiple user information at once. Using MSET has the following advantages over using SET commands multiple times: 1. Improve efficiency and reduce network round trips; 2. Ensure the atomicity of the operation (all success or failure); 3. Make the code more concise and easy to maintain. But two points should be noted: 1. MSET will overwrite existing keys, which may lead to data loss; 2. The command does not provide details

RedisCluster achieves horizontal expansion through data sharding, dividing the key space into 16,384 hash slots, each node is responsible for a portion of the slots. 1. Automatic data sharding: Use the CRC16 algorithm to map keys to specific slots to avoid single-point bottlenecks; 2. Distributed architecture: No central coordinator, communication between nodes through gossip protocol, supporting master-slave replication to ensure high availability; 3. Automatic rebalancing: Automatically reassign slots when adding and deleting nodes; 4. Client redirection: The client connects any node and is directed to the correct node. Deployment requires at least three master nodes, use the redis-cli command to create a cluster and configure a client driver that supports the cluster. Common problems include multi-key operations that need to coexist, network partitioning may cause brain splits,

BRPOPLPUSH is suitable for blocking task queues, atomic data transfers and simulated delay queue scenarios. 1. Implement a task queue with blocking: In the producer-consumer model, this command allows consumers to automatically block and wait when there is no task, avoiding wasting resources; 2. Move elements atomically and retain backups: Ensure that the process of taking out elements from one list and inserting into another list is uninterrupted, suitable for scenarios where task processing fails to be retryed or analyzed; 3. Used to implement circular queues or delay queue logic: By combining additional judgment logic, lightweight delay queues can be simulated, and the task can be determined according to conditions.