A programmer who's been working for five years and has been complaining to me in private letters. He says he's been using Mybatis for so long, and he's been good at Mybatis. It turns out he's flipped on the interview!

A programmer who's been working for five years, constantly complains to me in a private letter.

He said that he had used Mybatis for so long that he was good at Mybatis.

I can't believe I lost my car on Mybatis!

Well, let's look at the "Cache mechanism in Mybatis" today.

This is a complicated question, and I intend to explain it in a few ways.

First, a secondary cache was designed in Mybatis to enhance the efficiency of data retrieval and avoid the need to search the database for every data visit.

First-level cache, SqlSession level, is also called local cache because each user needs to use SqlSession to perform the query.

To avoid checking the database every time, Mybatis saves the queryed data in SqlSession's local cache, which the subsequent SQL can read directly from the local cache if hit.

If you want to achieve a cache across the SqlSession level? So a first-level cache cannot be achieved, so a second-level cache has been introduced in Mybatis, which is when there are multiple users.

When searching for data, only one SqlSession gets the data and puts it in a secondary cache, and the other SqlSession can load the data from the secondary cache.

The practical realization principles for each level of cache are:

Holds an Execulator in SqlSession, and every Execctor has a LocalCache object.

When the user initiates the query, Mybatis will search in Local Cache according to the executory statement and, if hit, then go to the database and write to LocalCache, otherwise return directly.

So the life cycle of the cache is SqlSession, and in multiple Sqlssession or distributed environments it may lead to dirty data in database writing.

The practical realization of the secondary cache is:

The Execulator is decorated using CachingExeculator, so that the secondary cache search is done through CachingExecctor before entering the first level cache query process.

When a secondary cache is opened, it is shared by multiple SqlSession, so it is a global cache. Its query process is to check the secondary cache, then the first cache, and then the database.

In addition, the secondary cache of MyBatis achieved the sharing of cache data between SqlSession relative to the primary cache, while the cache particle size was able to reach the namespace level, as well as different class combinations through the Cache interface, with greater control over Cache.

In the actual business scene, the design ideas of multiple-level caches are highly worthy of our learning and learning.

It should be borne in mind that the purpose of learning about bottom-level technologies is to enhance technological thinking and build up solutions that will pave the way for later higher positions.

This is the end of the popular VS interview series.

Any technical interviews you don't know, you're welcome to trust me.

If this article helps you, please pay some attention and praise, and you insist that I am the driving force behind it.

Tell me about the cache in Mybatis.