Grails\Hibernate: To cache or not to cache?

Question

What is the best caching policy in Hibernate\Grails. Cache all entities and queries or not and how to find best solution ?

Here my hibernate config.

hibernate {
  cache.use_second_level_cache = true
  cache.use_query_cache = true
  cache.provider_class = 'org.hibernate.cache.EhCacheProvider'
  connection.useUnicode = true
  connection.characterEncoding = 'UTF-8'
  connection.provider_class = 'org.hibernate.connection.C3P0ConnectionProvider'
  dialect = 'org.hibernate.dialect.MySQL5InnoDBDialect'
  order_updates = true
  c3p0.min_size = 5
  c3p0.max_size = 20
  c3p0.max_statements = 20 * 10
  c3p0.idle_test_period = 15 * 60
}

Ehcache config

<defaultCache
        maxElementsInMemory="10000"
        eternal="false"
        timeToIdleSeconds="120"
        timeToLiveSeconds="120"
        overflowToDisk="true"
        maxElementsOnDisk="10000000"
        diskPersistent="false"
        diskExpiryThreadIntervalSeconds="120"
        diskSpoolBufferSizeMB="100"
        memoryStoreEvictionPolicy="LRU"
/>

<cache
            name="org.hibernate.cache.StandardQueryCache"
            maxElementsInMemory="50"
            eternal="false"
            timeToLiveSeconds="120"
            overflowToDisk="true"
/>

Answer 1

The best caching policy is: no caching. Seriously, caching (and any optimization) should be done only to solve an existing problem. If you don't have performance problems, don't use caching. If you do have performance problems, then apply this simple 5-step procedure for solving performance problems:

1. Measure.
2. Measure.
3. Optimize (add caching, for example)
4. Measure.
5. Measure.

Note that if you don't understand how the caching works in Hibernate, you can end up having poor performance, instead of improving it. Also, even if you understand how caching works in Hibernate, there may be other effects influencing the performance, causing a database roundtrip to be faster than looking up the cache. That's why you should measure before and after doing "improvements".