5 minutes to explain what is redis?

Definition

Redis It's fast 、 Open source 、 In memory Key value data structure storage .

REDIS Allows you to RAM Store key value pairs on , Because of the visit RAM Faster than accessing disk 150,000 times , Comparison visit SSD fast 500 times , That means speed .

however , We have used... In most operations RAM！

But when it comes to caching or database interaction , We use disk by default , Imagine accessing a database to read 10,000 Bar record , If the data is stored on disk , The average need is 30 second , And from RAM Reading takes approximately 0.0002 second .

That means it's an ultra fast read / Write system , But because it's stored in RAM in , So it's volatile .

that , Will we lose data ？

To prevent data loss , There is a built-in persistence module , It will write the memory state to the dump file on disk under given conditions , Dump files are loaded at system startup , Once it's up and running , Data can be used to operate , therefore , No data loss .

We can use different configurations in multiple instances , To allow us to maintain continuous uptime through the so-called sentinel and master-slave architecture .

Redis yes Remote Dictionary Server The acronym for .

let me put it another way , It's a tool , Let you in RAM Store database on .

When and where to use Redis？

because Redis Fast as lightning , Therefore, it is mainly used for caching purposes , It is Redis The most shining place , Because it provides various types that can be stored through dictionary structure .

We can use Redis Cache complete pages with high traffic and static content , If the page itself is easy to change or the content is generated dynamically , Then you shouldn't cache it anyway , Whether we use Redis still Memcached. If the page mainly contains static content or every x Refresh the content once in a while , Then we can cache the page and provide it immediately ！

Where to use Redis My first priority is Full page caching (FPC).

Another thing it can do is Storage session , With no persistence Memcached Different ,Redis Have it and allow session storage , Use Redis Processing sessions can improve the user experience when interacting with the site .

Persistence is important for storing sessions , To avoid losing data in key parts of user interaction , for example , Process payment 、 Add items to the shopping cart or request any action as an authenticated user .

The second is Session cache .

Redis Run as a process , And MySQL、PHP、Apache Run the same way as all other services , It uses a lot of RAM Memory , If the server needs more space for heavy upgrade , Then it may choose to kill Redis The process of , under these circumstances , We will experience service downtime and possible data loss , To prevent this from happening ,Redis Built in Master-Slave framework .

This architecture allows us to have additional processes to monitor our main processes , Imitate its commands from the process , Occasionally, the main dump file is copied , To maintain consistency between processes . These monitoring processes are called Slaves, And the main thing is Master.

When the main process is killed , One of the slave processes becomes the master process and handles all requests when the master process restarts , once Master Start again , It will be from Temporary Master Get the dump file and use it as the base , The main process re instantiates the main process , The temporary master process changes back to the slave process again .

But how do we know when the main process is down ？ How do we know which Slave Should be master？

Sentinel Yes, it has the function of checking Redis The process of whether the instance is working properly , They are responsible for ：

• testing Master Is it down? ;
• Choose who is the temporary master ;
• monitor Master When to return and tell it which dump file to load .

sentry , I guess the name says everything .

General settings usually use a Master、 Two Slave And three Sentinel.

Redis Have a good community and well written documents , If you want to try , You will find a lot of support on their official website .

Redis Official website ：

https://redis.io/