Mybatis Cache

Note : For spring and mybatis integration, mybatis session is tied to spring transaction

Second Level Cache

1. Cached object has to be implemented Serializable
2. add <cache /> in sql xml file
3. session2 only can get cached object after session1 close or commit
4. <select>, <insert>, <update> and <delete> have flushCache attribute to clear cache after execute this statement. <select> has useCache="false" to desiable cache this select result
5. By default, <insert>, <update> and <delete> of same namespace will clear 2nd cache, developer can use flushCach="true" to disable this feature
6. Use LRU(Least Recently Used) to clear 2nd cache
7. <cache readOnly="true" /> means return reference of cached object to caller, while false means return copy instance of cached object, defaulst is false.
8. <cache-ref namespace="..." /> share 2nd cache config/instance

Custom Cache

• Implements Cache intertace
• <cache type="XX.CustomCache"><property name="cacheFile" value="..." /></cache>
• eviction strategy, readOnly etc are not applicable for custom cache

Mybatis and Ehcache Integration

1. add mybatis-ehcache.jar and ehcache.jar
2. add ehcache xml file
3. <cache type="...ehcache.."/>

Note : mybatis-ehcache-1.1.0 not support ehcache 3.X

2nd Cache Risk

Second level cache has risk at multiple tables query, please refer to this and this in Chinese. Even developer can use <cach-ref /> to avoid this risk, but 2nd level cache become more meaningless in this case because operation of multiple namespace will affect cache.

Therefore, it is a good practice to use cache in business service layer without mybatise cache.