1.1 What are the components of the JVM and what is the execution process?

From the diagram, we can see the main components of the JVM:

• ClassLoader
• Runtime Data Area
• Execution Engine
• Native Method Library

Execution process:

1. The ClassLoader converts Java code into bytecode.
2. The Runtime Data Area loads the bytecode into memory. The bytecode file is merely a set of instruction specifications for the JVM and cannot be directly executed by the underlying system; it requires the Execution Engine to run.
3. The Execution Engine translates the bytecode into low-level system instructions, which are then executed by the CPU. At this point, it may need to call the Native Method Library to implement the functionality of the entire program.

Single Sign-On (SSO) and Authentication Guide

1. Single Sign-On (SSO)

Definition

• Single Sign-On (SSO) is an authentication method
• Allows users to access multiple systems with one set of credentials
• Providing centralized login across different applications

1.1 What is the difference between threads and processes?

• A process is an instance of a running program, which contains threads, each executing different tasks.
• Different processes use different memory spaces, while all threads within the current process can share the same memory space.
• Threads are lighter; the cost of context switching between threads is generally lower than that of context switching between processes (context switching refers to switching from one thread to another).

1. What is cache penetration? How to solve it?

• Answer: Um, let me think. Cache penetration refers to querying a certain non-existent data. Since the storage layer cannot find the data, it does not write to the cache, which will cause this non-existent data to query the DB every time, potentially leading to the DB crashing. This situation is likely an attack. The solution we usually use is a Bloom filter to solve it.

1. How does RabbitMQ ensure message delivery without loss?

• Answer: We use RabbitMQ to ensure data dual-write consistency between MySQL and Redis, which requires us to implement high availability for messages. Specific measures include:
  1. Enable producer acknowledgment to ensure messages are delivered to the queue; if there is an error, log it and fix the data.
  2. Enable persistence to ensure messages are not lost in the queue before consumption; persistence needs to be applied to the exchange, queue, and the message itself.
  3. Enable automatic acknowledgment for consumers and set retry counts. For example, we set 3 retries; if it fails, the message is sent to an exception exchange for manual processing.

Array is a linear data structure that stores data of the same data type in contiguous memory space.

Addressing formula arr[i] = baseAddress + i * dataTypeSize

• baseAddress: the starting address of the array
• dataTypeSize: represents the size of the element type in the array, currently the array stores int type data, dataTypeSize = 4 bytes
• arr: refers to the array
• i: refers to the index of the array

1. Are singleton beans in the Spring framework thread-safe?

Answer:
No, they are not thread-safe. When multiple users request a service simultaneously, the container allocates a thread for each request, and these threads concurrently execute business logic. If the logic modifies the singleton's state (e.g., updating a singleton's member property), thread synchronization must be handled explicitly.

1. What are the five main components of Spring Cloud?

Answer:
Initially, the five key components of Spring Cloud were:

• Eureka: Service registry.
• Ribbon: Client-side load balancer.
• Feign: Declarative service invocation.
• Hystrix: Circuit breaker.
• Zuul/Gateway: API gateway.

1. How to Identify Slow Queries in MySQL

Answer:
During our stress testing, we noticed that some API responses were very slow, exceeding 2 seconds. Since our system integrates with SkyWalking/Prometheus for monitoring, its reports helped identify slow APIs and pinpoint which part of the API (including SQL execution) was slow.