Parsing the cache schema in a Java Distributed System (top)

Author Chen Yaahua article reprint exchange please contact [email protected]

This paper mainly introduces the related theory of cache in large-scale distributed system, the common caching components and the application scenarios.

1 Caching Overview

2 Classification of the cache

The cache is mainly divided into the following four categories

2.1 CDN CacheBasic Introduction

The basic principle of CDN (content Delivery Network) is that various cache servers are widely used to distribute these cache servers to regions or networks where users have access to a relatively centralized network, and when users visit a website, Leverage global load technology to point users ' access to the closest working cache server, which responds to user requests directly from the cache server

Application Scenarios

Main cache static resources, examples, video

application Diagram

Advantages

2.2 Reverse Proxy CacheBasic Introduction

The reverse proxy is located in the application server room and handles all requests to the Web server. If a user requests a page that has buffering on the proxy server, the proxy server sends the buffered content directly to the user. If there is no buffering, a request is made to the Web server, the data is retrieved, and the local cache is sent to the user. Reduces the load on the Web server by reducing the number of requests to the Web server.

Application Scenarios

Generally cache only small static file resources, such as CSS, JS, pictures

application Diagram

Open Source Implementation

2.3 Local App CacheBasic Introduction

Refers to the cache component in the application, the biggest advantage is that the application and the cache is within the same process, the request cache is very fast, there is no excessive network overhead, etc., in a single application does not require cluster support or cluster in the case of each node without mutual notification of the scenario of the use of local cache is more appropriate; Its disadvantage is that the cache should be coupled with the application, multiple applications cannot directly share the cache, each application or cluster nodes need to maintain their own separate cache, memory is a waste.

Application Scenarios

Common data such as cache dictionaries

Cache Media

ImplementDirect implementation of programming

EHCACHEBasic Introduction

Ehcache is?? A standard-based, open-source cache that improves performance, unloads databases, and simplifies scalability. It is the most widely used Java-based cache because it is powerful, validated, fully functional, and integrates with other popular libraries and frameworks. Ehcache can be extended from in-process cache to hybrid in-process/out-of-process deployments using terabytes of cache

Application Scenarios

Ehcache Architecture Diagram

main characteristics of Ehcache

ehcache Cache data Expiration policy

Ehcache Expiration Data elimination mechanism

Lazy elimination Mechanism: each time the cache into the data, there will be a period, in the read time and set the time to do a TTL comparison to determine whether the expiration

Guava CACHE2.4 Distributed CacheBasic Introduction

Guava cache is a caching tool in the Google Open source Java Reuse Toolset Library Guava

Features and Functions

Application Scenarios

data structure diagram

Cache Update Policy

Cache Recycling Policy

2.4 Distributed Cache

Refers to a cache component or service that is decoupled from the application, with the greatest benefit of being a standalone application that is isolated from the local application and that multiple applications can share the cache directly.

Main application Scenarios

Main access Mode

The following describes the 2 major open source implementations of distributed cache memcached and Redis

MemcachedBasic Introduction

Memcached is a high performance, distributed memory object caching system that can be used to store data in a variety of formats, including images, videos, files, and database retrieval results, by maintaining a unified, huge hash table in memory. The simple thing is to call the data into memory and then read it from memory, which greatly improves the reading speed.

features

Basic Architecture

Cache data Expiration policy

LRU (least recently used) expiration policy, when storing data items within memcached, you can specify the expiration time of the cache, which is permanent by default. When the memcached server runs out of allocations, the invalidated data is replaced first, and then the data that is not used recently.

Data obsolescence Internal implementation

Lazy elimination Mechanism: each time the cache into the data, there will be a period, in the read time and set the time to do a TTL comparison to determine whether the expiration

Distributed cluster Implementation

There is no "distributed" function on the server side. Each server is a fully independent and isolated service. Memcached distributed, is implemented by the client program

RedisBasic Introduction

Redis is a remote in-memory database (non-relational database) with strong performance, unique data model with replication characteristics and problem solving. It can store the mappings between key-value pairs and 5 different types of values, persist the data stored in memory to the hard disk, use the replication feature to extend read performance, and Redis can also use client shards to extend write performance. Built-in replication (replication), LUA scripting (LUA scripting), LRU driver events (LRU eviction), transactions (transactions), and different levels of disk persistence (persistence), and Redis Sentinel (Sentinel) and automatic partitioning (Cluster) provide high availability (HI availability).

Data Model

Data Retirement Strategy

Data obsolescence Internal implementation

Persistence mode

partial parsing of the underlying implementation

Pictures from csdn Blogger-god restricted area, if there is any fairy who knows what drawing software to draw the welcome comment, I also want to know.

• Part of the process diagram that starts

• Partial operation diagram of server-side persistence

• Underlying hash table implementation (progressive rehash)

Initialize Dictionary

New Dictionary element plot

Rehash Execution Process

Caching Design Principles

comparison of Redis and memcached

Parsing the cache schema in a Java Distributed System (top)