Initial experience of cache and ehcache "suggestions collection"

Hello everyone , I meet you again , I'm the king of the whole stack .

1. The meaning of caching

The caching mechanism is to take out the data often used in the database and put it into memory . When the program is called, it fetches directly from memory , Use every time Data access database , This improves efficiency .

2. Caching needs attention

1) Cache update

The data in the cache must be consistent with the data in the database .

2) Cache hit rate

Improve the utilization of cached data , The cache stores data that users often use , Suppose that the cache stores something that users don't often use . Then the hit rate of cache is not high . Sometimes , It is the high utilization rate of some cached data at a certain time , Low utilization at a certain time , So it needs to be updated constantly , To improve cache hit ratio .

Hibernate Cache mechanism

• The first level cache is Session The cache of . because Session The life cycle of an object usually corresponds to a database transaction or an application transaction , So its cache is a transaction wide cache . First level caching is necessary , Disagree and can't be removed . In the first level cache . Each instance of a persistent class has a unique OID. • The second level cache is a pluggable cache plug-in , It consists of SessionFactory Responsible for managing the . because SessionFactory The life cycle of the object corresponds to the whole process of the application , So the second level cache is Process wide cache . This cache stores the bulk data of the object .

The second level cache is optional . The second level cache can be configured on the granularity of each class or collection .

remarks ：

L1 cache may cause repeated data queries , thus , We introduced the second level cache mechanism .

The first level cache is used by user threads . The L2 cache is shared by everyone .

What we need to learn is how to control the L2 cache , To this end, we need to ensure 2 spot ：

1). How to update the data in the L2 cache Suppose the user does not change the data of the database , We need to update the cache immediately 2). Ensure the hit rate of data in L2 cache Change space for time .

Data in L2 cache

When necessary, we use frequent data .

3.EhCache

1. Brief introduction

EhCache It's pure. Java In process caching framework for . With high speed 、 Characteristics such as ability . yes Hibernate In the default CacheProvider.

2. stay Hibernate Use in EhCache

Change profile Hibernate.cfg.xml

<property name="hibernate.cache.provider_class">
org.hibernate.cache.EhCacheProvider
</property>

Copy

3. The configuration file ehcache.xml

The meanings of parameters are • maxElementInMemory Indicates how many objects can be placed in the cache , Here is 10000 individual , It can be configured according to the amount of memory • eternal Indicates whether to set these data objects put into the L2 cache to be permanent （ Put it in and save it . No longer clear ） Typically for false • timeToIdleSeconds=120 It is assumed that 120 Seconds . The placed object is not accessed again , Just clear it out • timeToLiveSeconds=120 Indicates the time the object survives in the cache , An object enters this cache 120 Seconds later , It will be cleared away by itself （ Generally, the setting time will be longer than timeToIdleSeconds Long time ）.

This property is set to allow many other active objects to enter From cache . • overflowToDisk=”true” Indicates that the assumed active object has exceeded maxElementInMemory Set the maximum value of , Exceeded objects are written Save it on your hard disk . Ease the situation with more active users .

4. Change the detailed mapping file xxx.hbm.xml

Join the familiar ：<property region=”default” usage=”read-write”>

• region attribute Indicates which L2 cache to use • usage attribute Indicates how L2 cache is used There are two kinds of ：read-only and read-write read-only Let's say it's read-only. Then it cannot be changed . such ehcache There is no need to consider the operation of changes and updates . read-write Set to read-write,ehcache Also consider updates and changes . This will reduce efficiency .

therefore . Set up usage Attributes are very important , It is necessary to infer that the stored objects use L2 cache based on the actual situation .

Welcome to discuss and study together ！

Practical self collection !

Record and share . Let us grow together ！ Welcome to my other blogs . My blog address ：http://blog.csdn.net/caicongyang

Publisher ： Full stack programmer stack length , Reprint please indicate the source ：https://javaforall.cn/116611.html Link to the original text ：https://javaforall.cn