This article explains why Redis memory usage stays high after deleting keys, describes memory fragmentation causes, shows how to detect fragmentation with INFO memory and mem_fragmentation_ratio, and provides practical steps and configuration options to clean and prevent fragmentation.
This comprehensive guide covers essential Redis interview topics, including persistence mechanisms (RDB and AOF), cache challenges such as avalanche, penetration and pre‑warming, data types and their use cases, internal structures, eviction policies, single‑thread performance, clustering solutions, distributed locking, transactions, and best practices for high‑traffic environments.
The article analyzes the extreme‑traffic challenges of China’s 12306 ticket‑spike service, presents a layered load‑balancing architecture using OSPF, LVS, and Nginx weighted round‑robin, and demonstrates a Go‑based prototype that combines local in‑memory stock deduction with Redis‑backed global stock control to achieve stable, high‑throughput ticket purchasing without overselling.
This article explains Redis's event-driven architecture, detailing file and time events, their processing flow, and why Redis 6.0 introduced multithreading to improve network I/O while keeping command execution single‑threaded.
This article provides a step‑by‑step guide for manually building a six‑node Redis cluster on macOS, detailing environment setup, configuration changes, node startup, slot allocation, and converting master nodes to slaves, with screenshots and command examples.
This article explains how to use Redis sets, sorted sets, bitmaps, and HyperLogLog for various aggregation, sorting, binary state, and cardinality statistics, providing concrete command examples, design patterns, and performance considerations for large‑scale applications.
This guide walks you through downloading, extracting, compiling, and installing Redis from source on Ubuntu, configuring its files and startup scripts, securing the service, enabling automatic boot start, and performing data migration with detailed commands and examples.
This article explains the mechanisms of Redis master‑slave data synchronization—including full and partial resynchronization—details the internal workings of Redis clustering, slot assignment, automatic node detection, and failover recovery, and provides practical insights for building reliable Redis deployments.
Redis, an in‑memory C‑language database, offers ultra‑fast read/write speeds, rich data structures, persistence, clustering, and multi‑threaded I/O, making it ideal for distributed caching, locks, queues, and more; this guide explains its fundamentals, comparisons with Memcached, data types, eviction policies, and operational best practices.
This article introduces Redis's eight fundamental data types—String, List, Set, Hash, Sorted Set, Geospatial, HyperLogLog, and Bitmap—explaining their characteristics, typical use‑cases, and providing concrete command‑line examples that demonstrate creation, manipulation, and querying of each type.
This article outlines five practical methods for synchronizing MySQL data to external systems such as Elasticsearch, Redis, and message queues, covering business‑layer hooks, middleware integration, scheduled tasks using updated_at, binlog parsing with ROW format, and handling mixed or statement binlog formats, plus open‑source tools.
This article explains the concept and common use cases of delayed messages and compares five practical implementation methods—using Redis sorted sets, RabbitMQ delayed‑message exchange plugin, ActiveMQ scheduled messages, RocketMQ fixed delay levels, and a custom RocketMQ solution—detailing their workflows, advantages, and drawbacks.
This article provides a comprehensive guide to Redis for interview preparation, covering persistence mechanisms, common caching challenges such as avalanche and penetration, data types and their use cases, internal structures, expiration policies, single‑threaded performance, clustering options, distributed locking, and best‑practice solutions.
This guide reviews Redis's eight fundamental data types—String, List, Set, Hash, Sorted Set, Geospatial, HyperLogLog, and Bitmap—explaining their commands, usage scenarios, and practical examples to help developers and interviewees master this popular NoSQL database.
This article explains how to prevent and gracefully handle duplicate requests on the server side by using unique request IDs with Redis, generating MD5 digests of request parameters, and provides a reusable Java helper class with code examples and testing logs.
This article explains Redis's cache expiration policies—including timed, periodic, and lazy eviction—details the internal structure and parsing of RDB files, and describes the AOF persistence mechanism with its write‑ahead logging, synchronization options, and rewrite process, providing a comprehensive view of Redis data durability.
This article explains how to use Zabbix Agent2 to monitor Redis, covering the plugin's architecture, configuration priority, methods for retrieving INFO, CONFIG, health status, and slow‑query logs, as well as practical steps to set up the Redis template in Zabbix.
This article walks through a practical approach for front‑end engineers to cut down a sluggish legacy API from over three seconds to under a second by adding a Node.js proxy layer that leverages GraphQL field selection, Redis caching, and a scheduled cache refresh.
This article introduces Redis as a high‑performance, in‑memory NoSQL database, explains why learning it is valuable, provides step‑by‑step installation instructions, and presents essential commands for keys, strings, lists, sets, sorted sets, and hashes with practical code examples.
This article explains Redis's two persistence mechanisms—AOF (Append Only File) and RDB (snapshot)—detailing their concepts, write‑back strategies, rewrite process, performance trade‑offs, snapshot handling, copy‑on‑write technique, incremental snapshots, and the benefits of combining both approaches.
This article narrates how Redis, personified as a character, synchronizes data between master and slave nodes through command propagation, adopts improved sync strategies, and uses Sentinel's INFO and PING checks to detect failures and automatically trigger failover, illustrating a practical high‑availability cache service.
This article provides a comprehensive guide to Redis persistence mechanisms, detailing how RDB snapshots and AOF logs work, how to configure and use them, their advantages and drawbacks, and how to choose the right approach for reliable data storage.
This article details Xiaomi's migration of tens of thousands of Redis instances from physical servers to Kubernetes, explaining the motivations for containerization, the deployment architecture with StatefulSets and a custom Redis Proxy, performance comparisons of proxy options, operational challenges, and the resulting benefits in resource utilization, automation, and service stability.
This page continuously gathers and organizes over 200 Java backend interview Q&A articles, covering topics such as Spring, Redis, MySQL, concurrency, design patterns, and system design, providing a valuable resource for candidates to review before interviews.
This tutorial explains how to install Redis on Linux (including source compilation and Docker), set it up as a daemon, install the PHP Redis PECL extension, configure Composer, install ThinkPHP5, and run a simple PHP script that stores and retrieves a value from Redis.
This article explains why using the KEYS command on massive Redis datasets can cause service blockage, analyzes the underlying O(n) traversal cost, and demonstrates how the incremental SCAN command with cursor, MATCH, and COUNT options provides a non‑blocking alternative for efficiently iterating keys.
This article examines common techniques for implementing a user check‑in function in web and mobile applications, comparing a straightforward MySQL table solution with a Redis bitmap approach, detailing the data structures, code examples, workflow, and the advantages and disadvantages of each method.
This article explores the architecture and implementation of a high‑concurrency ticket‑spike system, covering load‑balancing strategies, Nginx weighted round‑robin configuration, local stock deduction in Go, remote stock control with Redis Lua scripts, and performance testing results.
The article explains how a single‑machine Java lock can cause inventory oversell in a distributed e‑commerce system, introduces the concept of a global distributed lock, and compares practical implementations using Redis (including RedLock and Redisson) and Zookeeper (with Curator), highlighting their trade‑offs and selection guidelines.
This guide walks through checking your PHP configuration, downloading the appropriate Redis extension, installing it, updating php.ini, verifying the installation, starting the Redis service, and shows the core template and PHP server code needed to implement a historical search queue using Redis.
This article explains why Redis uses a custom SDS string structure instead of native C strings, describes the SDS layout, expansion rules, redisObject metadata, and the three string encodings (int, embstr, raw) that optimize performance and memory usage.
This guide explains seven critical Linux operating‑system settings—memory overcommit, swappiness, Transparent Huge Pages, OOM killer, NTP synchronization, ulimit, and TCP backlog—that together ensure Redis runs reliably and at peak speed.
This guide demonstrates how to set up a Redis multi-database singleton wrapper in a ThinkPHP project, covering prerequisite installation, configuration of connection parameters, creation of a custom Redis class with static instance management, and example usage of Redis commands across different databases.
This article explains the cache breakdown problem, introduces Laravel 7's built‑in RedisLock class, details its constructor parameters, and provides a complete code example demonstrating how to acquire and release a Redis lock to safely populate and update cached data.
This article explains the typical reasons behind Redis latency spikes—such as complex commands, big keys, concentrated expirations, memory limits, fork overhead, CPU binding, AOF settings, swap usage, and network overload—and provides practical steps and monitoring techniques to identify and resolve each problem.
The October 2020 Spring Data Ockham (2020.0.0) release introduces a new version‑naming scheme, updates to Spring Data Neo4j, JDBC, R2DBC, Redis, adds RxJava 3 and De‑lombok support, and outlines compatibility notes for Spring Boot 2.4 and Neo4j users.
This article provides a comprehensive guide to advanced Redis operations, covering pipeline usage, transaction handling, publish/subscribe mechanisms, key migration techniques, custom command implementation with Jedis, and efficient key scanning methods, complete with code examples and performance comparisons.
This article shares a developer's job‑search journey and detailed interview recap, covering project experience, Java collections, HashMap vs Hashtable, synchronized and volatile, singleton patterns, thread‑pool types, Spring Boot AOP, and Redis caching concepts, illustrated with diagrams.
This article explains how to replace a 29‑day serial processing job for 100,000 string records with a Redis‑backed asynchronous task queue powered by Node.js, PM2 clustering, and distributed locking, achieving a ten‑second runtime for 20 sample tasks.
This guide demonstrates how to use Python's redis module to manipulate all major Redis data structures—strings, lists, sets, sorted sets, and hashes—detailing each command, providing clear code examples, and showing expected output for practical learning.
This article explains why Redis clusters are needed, how CLUSTER MEET builds the network, slot assignment, scaling procedures, client redirection mechanisms, batch operations, fault detection, recovery processes, and common operational pitfalls, providing practical guidance for building and maintaining a robust Redis Cluster deployment.
This tutorial demonstrates how to use Redis SET operations and a Lua script to implement a lottery mechanism, and shows how to integrate the script into a Java Spring application using Spring Data Redis's RedisTemplate for atomic execution.
This article explains how Redis introduced Lua scripting to combine multiple commands atomically, covers Lua basics, data types, control structures, script execution with EVAL/EVALSHA, script management commands, and practical tips for writing efficient, safe Redis Lua scripts.
This guide explains how to use Redis key expiration notifications in a Spring Boot application to automatically close unpaid orders by storing an order‑ID key with a TTL, configuring Redis to emit expiration events, and implementing a listener that updates order status when the key expires.
This article examines the challenges of building a flash‑sale (秒杀) system—such as overselling, high concurrency, request throttling, and database strain—and presents a comprehensive backend design using separate databases, dynamic URLs, static pages, Redis clustering, Nginx, token‑bucket rate limiting, asynchronous order processing, and service degradation strategies.
This article explains common causes of Redis latency spikes, such as high‑complexity commands, large keys, concentrated expirations, memory limits, fork overhead, CPU binding, AOF settings, swap usage, and network saturation, and provides step‑by‑step troubleshooting commands and best‑practice recommendations.
This guide walks through the complete deployment of Spinnaker on Kubernetes using Halyard, covering architecture analysis, preparation of Redis, MySQL and MinIO, container image retrieval, BOM preparation, Halyard configuration, external Redis and SQL database integration, authentication, canary analysis, monitoring, and additional settings.
This article provides a comprehensive overview of Redis interview topics, covering persistence mechanisms, cache avalanche and penetration problems, hot and cold data concepts, differences from Memcached, single‑thread performance, data structures, expiration policies, clustering solutions, distributed locks, transactions, and practical troubleshooting tips.
This article details a production incident where Redis memory usage surged due to improper Set serialization, explains the investigation of storage structures and capacity formulas, and outlines a step‑by‑step data migration and cleanup process to restore normal operation.
This article explains the three major Redis cache problems—cache penetration, cache breakdown, and cache avalanche—describes their causes, illustrates solutions such as empty-object caching, Bloom filters, locking, and provides practical code examples and mitigation strategies.
This article explains why Redis, a single‑threaded server, adopts I/O multiplexing to avoid blocking, compares blocking I/O with multiplexed models, and details the internal implementation of select, epoll, and kqueue wrappers that power Redis's high‑performance event loop.
This article explains the concepts of cache penetration, cache breakdown, and cache avalanche in Redis, and provides practical mitigation strategies including null caching, distributed locks, random expiration times, and the use of Bloom filters to reduce database load.
This article explains the internal structure of Redis dictionaries, how elements are added, and how rehash-based resizing works, drawing parallels with Java's HashMap to help interviewees answer related questions effectively in technical interviews.
This article examines the typical reasons Redis latency spikes—such as high‑complexity commands, big keys, concentrated expirations, memory limits, fork overhead, CPU binding, AOF settings, swap usage, and network saturation—and provides practical diagnostics and mitigation steps to keep Redis responsive.
This guide explains how to configure Redis Sentinel to monitor master‑slave instances, automatically promote a slave on master failure, and verify the high‑availability setup with detailed configuration files, startup commands, status checks, and failover testing steps.
This page provides a comprehensive collection of links to over a hundred interview‑focused articles covering Java, Spring, Redis, MySQL, concurrency, design patterns, and other backend development topics, organized by issue number for easy reference.
This article compares Redis and Memcached across thread models, data structures, eviction policies, pipelines, persistence, high availability, and clustering, helping developers choose the most suitable in‑memory database for their specific workload and performance requirements.
This article explains the typical reasons for Redis latency spikes—including complex commands, large keys, expiration bursts, memory limits, fork overhead, AOF settings, swap usage, and network saturation—and provides practical steps and commands to identify and mitigate each issue.
This article explains why Redis can become slow, covering typical latency causes such as high‑complexity commands, large keys, concentrated expirations, memory limits, fork overhead, CPU binding, AOF settings, swap usage, and network saturation, and provides practical troubleshooting steps and best‑practice recommendations.
This article explains the three major cache issues—penetration, breakdown, and avalanche—describes why they occur in high‑traffic systems, and presents four practical mitigation strategies including Bloom filters, short‑lived empty caches, distributed mutex locks with Redis or Memcache, and resource isolation with Hystrix.
This article explains why using Redis's KEYS command can block other operations, illustrates the underlying single‑threaded execution model, and shows how upgrading shiro‑redis to use the SCAN command avoids performance issues in distributed session management.
This article explains the concept of API idempotency, reviews common solutions, and provides a complete Spring Boot implementation using a Redis‑based token mechanism, custom @ApiIdempotent annotation, interceptor, and supporting services, along with testing and important concurrency considerations.
This article explains how to automatically renew JWT tokens in a front‑end/back‑end separated system by storing tokens in a cache, checking them in a filter, and refreshing them when expired, thereby preventing frequent logins and preserving form data.
The article explains how MySQL stores persistent data while Redis serves read‑only data, outlines read/write request handling, discusses consistency issues in low and high concurrency scenarios, and provides practical solutions such as cache invalidation, queue‑based updates, and deployment considerations.
This article explains why a multi‑level cache combining JVM‑level Caffeine and distributed Redis is essential for modern Spring Boot applications, outlines design challenges, provides step‑by‑step integration instructions, and demonstrates performance gains with benchmark results and core implementation code.
This article explains how Redis Sentinel provides automatic failover and high availability by using master‑slave replication, multiple Sentinel nodes, consensus‑based leader election, and client notification mechanisms to ensure continuous service despite node failures.
This article introduces Redis's advanced bitmap capabilities, detailing the SETBIT, GETBIT, BITCOUNT, and BITOP commands, their syntax, underlying SDS data structure, performance characteristics, storage calculations, and practical use cases such as user sign‑in tracking and online status monitoring.
The article narrates Redis’s journey to implement durable storage, contrasting RDB snapshotting and AOF logging, detailing configuration options, forked processes, and trade‑offs, while illustrating interactions with MySQL’s binlog to highlight persistence strategies and performance considerations.
The article explains how Redis caching boosts high‑concurrency applications by outlining common use cases such as counters, session storage, rate limiting, leaderboards and distributed locks, then details best‑practice guidelines, typical pitfalls like TTL overwrites and cache stampedes, and essential monitoring techniques for performance and reliability.
This tutorial explains how to upgrade a SpringBoot application from a single‑node Redis setup to a Redis cluster by adjusting configuration parameters, adding the correct Maven dependencies, injecting a RedisTemplate with JedisConnectionFactory, and providing a reusable utility class for common Redis operations.
This article explains why Redis latency can suddenly increase—covering high‑complexity commands, large keys, concentrated expirations, memory limits, fork overhead, CPU binding, AOF settings, swap usage, and network saturation—and provides practical diagnostic steps and mitigation techniques.
This article explains why native Java locks fail in multi‑node deployments, introduces the concept of a distributed lock, and compares two popular implementations—Redis (including RedLock and Redisson) and Zookeeper (with Curator)—detailing their mechanisms, code examples, advantages, drawbacks, and practical selection guidance.
This article walks through building a two‑level caching system in Java, starting with a generic cache interface, implementing a local Guava cache, then adding a Redis distributed cache, and finally combining them with versioned keys to achieve timely expiration and seamless cache switching.
This article explains why a Redis instance may experience sudden latency spikes, walks through diagnosing the problem with slow‑log and big‑key scans, and provides concrete configuration tweaks, command‑level best practices, and operational guidelines to keep Redis performing at peak speed.
This article examines typical Redis latency spikes—such as complex O(n) commands, large keys, concentrated expirations, memory limits, fork overhead, CPU binding, AOF settings, swap usage, and network saturation—explaining how to detect, monitor, and mitigate each issue to maintain high‑performance operation.
This article explains why a high‑performance Redis instance can suddenly experience high latency, covering complex commands, large keys, expiration bursts, memory limits, fork overhead, CPU binding, AOF settings, swap usage, and network saturation, and provides practical troubleshooting and mitigation steps.
This article explains how Redis, created to alleviate MySQL’s read‑heavy load, provides in‑memory caching, various data structures, expiration policies, eviction strategies, Bloom‑filter protection against cache penetration, and techniques to prevent cache breakdown and avalanche, improving overall system performance.
This guide walks you through creating and using a one‑click installation package that sets up essential development services—MySQL, Nginx, JDK, Redis, RabbitMQ, and a SpringBoot jar—on Ubuntu 16.x, detailing directory structure, required prerequisites, individual start/stop scripts, and customization options for small‑scale deployments.
This guide introduces AnotherRedisDesktopManager, a free and visually appealing Redis GUI that supports cluster connections, walks through installation from GitHub, explains key features such as dark mode, command console, and versatile data operations for strings, lists, and hashes, and demonstrates practical cluster usage.
This article explains the concept of API idempotency, outlines common solutions, and provides a complete Spring Boot implementation using Redis and a token mechanism, including custom annotation, interceptor, utility classes, and testing procedures to ensure safe, single‑execution requests.
This article reviews six practical URL deduplication methods—including Java Set, Redis Set, database queries, unique indexes, Guava Bloom filter, and Redis Bloom filter—explaining their principles, providing complete implementation code, and recommending the most suitable approach for different system scales.
This article explains the design and evolution of Redis's Simple Dynamic Strings (SDS), covering the original pre‑3.2 structure, the newer type‑specific headers, the core API functions for creating, clearing, and concatenating SDS objects, and the memory‑reallocation strategy that ensures binary safety and efficient storage.
This article explains the principles of primary keys, compares auto‑increment IDs and GUIDs, introduces the Snowflake ID structure, discusses its benefits and drawbacks, and provides a complete .NET implementation using Redis for dynamic worker‑ID allocation, including handling clock rollback and code examples.
This article explains how Redis Sentinel provides automatic failover by combining multi‑replica deployment, health monitoring, leader election, and distributed consensus to detect master failures, select a new master, promote it, and notify clients, ensuring high availability for Redis databases.
This tutorial walks you through downloading RuoYi-Vue 3.1, creating a MySQL database, importing required SQL files, configuring Redis and application settings, and then launching the Spring Boot back‑end and Vue front‑end so you can access the admin console at http://localhost:81/.
This article explains the concept of caching, why database caching with Redis is needed for MySQL, the consistency challenges it introduces, and compares four practical solutions—TTL, write‑through, message‑queue, and binlog replication—offering guidance on selecting the appropriate approach for different latency and reliability requirements.
This article explains Redis sharding, covering its purpose, various partitioning methods such as range and hash partitioning, implementation approaches like client‑side and proxy‑assisted sharding, their drawbacks, and practical steps for migration and using Redis Cluster or Twemproxy.
This article explains how to design and build a simple two‑level caching solution in Java, covering generic cache interfaces, local caching with Guava, distributed caching with Redis, configuration details, version‑controlled cache keys, and practical usage within a Spring Boot application.
This article examines a real flash‑sale incident where Redis distributed locks expired, causing overselling, analyzes the root causes such as lock safety and non‑atomic stock checks, and presents safer lock implementations, atomic stock operations, and architectural reflections to prevent future failures.
This article compiles common Redis interview questions, compares Redis with Memcached, explains eviction policies, and provides a concise introduction to distributed systems, high‑availability architectures, master‑slave replication, synchronization methods, and Redis‑based distributed lock solutions.
This article explains why caching is essential for high‑traffic MySQL applications, outlines the consistency challenges of using Redis as a cache, and compares four practical synchronization solutions—TTL‑only, write‑through, message‑queue‑based, and binlog‑driven—highlighting their advantages, drawbacks, and selection guidelines.
This article details the business flow analysis, functional decomposition, database schema, API design, and high‑concurrency implementation of a WeChat red‑packet and seckill system, showcasing Redis atomic decrement, Bloom filter usage, Lua scripts, JMeter load testing, and integration with SpringBoot.
This article explains Redis's asynchronous master‑slave replication, covering the three core mechanisms, partial and full resynchronization processes, configuration methods, diskless sync, key expiration handling, replication IDs and offsets, and safety considerations when disabling persistence.
This article details the end‑to‑end design, database schema, Redis atomic operations, Bloom filter integration, JMeter load testing, and SpringBoot implementation for a high‑concurrency WeChat red‑packet (抢红包) service, including flash‑sale (秒杀) techniques and Lua scripts for atomic stock handling.
This article provides an in‑depth technical overview of Redis, covering its core data structures, memory allocation strategies, eviction policies, persistence mechanisms (RDB and AOF), transaction model, sentinel and cluster architectures, Pub/Sub messaging, and multiple approaches to implementing distributed locks.
This tutorial explains how to implement a Redis distributed lock with SpringBoot and Jedis, covering lock creation using SETNX, expiration handling, safe unlocking via Lua scripts, and a 100,000‑user parallelStream simulation of a limited‑stock order‑grab scenario, complete with code samples and results.
The article shows how a Vue login page can request a SpringBoot endpoint that creates a four‑character captcha image, encodes it as a Base64 data URL, returns it together with a UUID, stores the code in Redis with a two‑minute expiration, and validates the UUID during login.
This article explains how to implement distributed session management, transaction handling, and locking mechanisms in Java applications, covering Tomcat‑Redis integration, Spring Session with Redis, various distributed transaction patterns, and both Redis and Zookeeper based distributed locks with complete code examples.
This article presents a comprehensive design of a flash‑sale system, covering business scenario analysis, high‑concurrency problems such as overselling and malicious requests, and detailed front‑end, Nginx, risk‑control, back‑end, database, and distributed‑transaction solutions to ensure reliability and performance.
This article explains how to use Redis and Redisson for distributed locking, introduces an abstract DistributedLock interface for flexible implementations, demonstrates automatic lock release with functional callbacks, and discusses fallback strategies and monitoring to ensure reliability in backend systems.
