1) Introduction
While working with Hibernate web applications we will face so many problems in its performance due to database traffic. That to when the database traffic is very heavy . Actually hibernate is well used just because of its high performance only. So some techniques are necessary to maintain its performance. Caching is the best technique to solve this problem. In this article we will discuss about, how we can improve the performance of Hibernate web applications using caching.
The performance of Hibernate web applications is improved using caching by optimizing the database applications. The cache actually stores the data already loaded from the database, so that the traffic between our application and the database will be reduced when the application want to access that data again. Maximum the application will works with the data in the cache only. Whenever some another data is needed, the database will be accessed. Because the time needed to access the database is more when compared with the time needed to access the cache. So obviously the access time and traffic will be reduced between the application and the database. Here the cache stores only the data related to current running application. In order to do that, the cache must be cleared time to time whenever the applications are changing. Here are the contents.
Hibernate uses two different caches for objects: first-level cache and second-level cache..
1.1) First-level cache
First-level cache always Associates with the Session object. Hibernate uses this cache by default. Here, it processes one transaction after another one, means wont process one transaction many times. Mainly it reduces the number of SQL queries it needs to generate within a given transaction. That is instead of updating after every modification done in the transaction, it updates the transaction only at the end of the transaction.
1.2) Second-level cache
Second-level cache always associates with the Session Factory object. While running the transactions, in between it loads the objects at the Session Factory level, so that those objects will available to the entire application, don’t bounds to single user. Since the objects are already loaded in the cache, whenever an object is returned by the query, at that time no need to go for a database transaction. In this way the second level cache works. Here we can use query level cache also. Later we will discuss about it.
2) Cache Implementations
Hibernate supports four open-source cache implementations named EHCache (Easy Hibernate Cache), OSCache (Open Symphony Cache), Swarm Cache, and JBoss Tree Cache. Each cache has different performance, memory use, and configuration possibilities.
2.1) 2.1 EHCache (Easy Hibernate Cache) (org.hibernate.cache.EhCacheProvider)
2.2)OSCache (Open Symphony Cache) (org.hibernate.cache.OSCacheProvider)
2.3)SwarmCache (org.hibernate.cache.SwarmCacheProvider)
2.4)JBoss TreeCache (org.hibernate.cache.TreeCacheProvider)
3) Caching Stringategies
Important thing to remembered while studying this one is none of the cache providers support all of the cache concurrency strategies.
3.1) Read-only
Advantage if this one is, It is safe for using in a cluster. Here is an example for using the read-only cache strategy.
<class name="abc.mutable " mutable="true ">
<cache usage="read-only"/> ....
</class>
3.2) Read-Write
Here is an example for using the read-write cache stringategy.
<class name="abc.xyz" .... >
<cache usage="read-write"/> …. <
set name="yuv" ... >
<cache usage="read-write"/> …. </set> </class>
3.3) Nonstrict read-write
Here is an example for using the nonstrict read-write cache stringategy.
<class name="abc.xyz" .... >
<cache usage=" nonstringict-read-write"/> …. </class>
3.4) Transactional
4) Configuration
For configuring cache the hibernate.cfg.xml file is used. A typical configuration file is shown below.
<hibernate-configuration>
<session-factory>
...
<property name="hibernate.cache.provider_class">
org.hibernate.cache.EHCacheProvider
</property>
... </session-factory>
</hibernate-configuration>
The name in <property> tag must be hibernate.cache.provider_class for activating second-level cache. We can use hibernate.cache.use_second_level_cache property, which allows you to activate and deactivate the second-level cache. By default, the second-level cache is activated and uses the EHCache.
5) <cache> element
The <cache> element of a class has the following form:
<cache usage=" caching stringategy" region="RegionName" include="all | non-lazy"/>
The <cache> element of a class is also called as the collection mapping.
6) Caching the queries
Until now we saw only caching the transactions. Now we are going to study about the caching the queries.Suppose some queries are running frequently with same set of parameters, those queries can be cached. We have to set hibernate.cache.use_query_cache to true by calling Query.setCacheable(true) for enabling the query cache. Actually updates in the queries occur very often. So, for query caching, two cache regions are necessary.
Query cache always used second-level cache only. Queries wont cached by default. Here is an example implementation of query cache.
List xyz = abc.createQuery("Query").setEntity("…",….).setMaxResults(some integer)
.setCacheable(true).setCacheRegion("region name").list();
We can cache the exact results of a query by setting the hibernate.cache.use_query_cache property in the hibernate.cfg.xml file to true as follows:
<property name="hibernate.cache.use_query_cache">true</property>
Then, we can use the setCacheable() method on any query we wish to cache.
7) Custom Cache
To understand the relation between cache and the application the cache implementation must generate statistics of cache usage.
7.1) Custom Cache Configuration
In the hibernate.properties file set the property hibernate.cache.provider_class = examples.customCache.customCacheProvider.
7.2) Implementation :: ExampleCustomCache
Here is the implementation of ExampleCustomCache. Here it uses Hashtable for storing the cache statistics.
package examples.ExampleCustomCache;
import net.sf.hibernate.cache; import java.util;
import org.apache.commons.logging;
public class ExampleCustomCache implements Cache {
public Log log = LogFactory.getLog(ExapleCustomCache.class);
public Map table = new Hashtable(100);
int hits, misses, newhits, newmisses, locks, unlocks, remhits, remmisses, clears, destroys;
public void statCount(StringBuffer input, String string1, int value) {
input.append(string1 + " " + value);
}
public String lStats() {
StringBuffer res = new StringBuffer();
statCount(res, "hits", hits);
statCount(res, "misses", misses);
statCount(res, "new hits", newhits);
statCount(res, "new misses", newmisses);
statCount(res, "locks", lock);
statCount(res, "unlocks", unlock);
statCount(res, "rem hits ", remhits);
statCount(res, "rem misses", remmisses);
statCount(res, "clear", clears);
statCount(res, "destroy", destroys);
return res.toString();
} public Object get(Object key) {
if (table.get(key) == null) {
log.info("get " + key.toString () + " missed");
misses++;
} else {
log.info("get " + key.toString () + " hit");
hits++; }
return table.get(key);
}
public void put(Object key, Object value)
{ log.info("put " + key.toString ());
if (table.containsKey(key)) {
newhits++;
} else {
newmisses++;
}
table.put(key, value);
}
public void remove(Object key)
{
log.info("remove " + key.toString ());
if (table.containsKey(key)) {
remhits++;
} else {
remmisses++;
} table.remove(key);
}
public void clear() {
log.info("clear");
clears++;
table.clear();
}
public void destroy()
{
log.info("destringoy ");
destroys++;
}
public void lock(Object key) {
log.info("lock " + key.toStringing());
locks++;
}
public void unlock(Object key) {
log.info("unlock " + key.toStringing());
unlocks++;
}
Here is the example of Custom Cache.
Package examples.ExapleCustomCache;
import java.util; import net.sf.hibernate.cache;
public class ExampleCustomCacheProvider implements CacheProvider {
public Hashtable cacheList = new Hashtable();
public Hashtable getCacheList() {
return cacheList;
}
public Stringing cacheInfo () {
StringingBuffer aa = new StringingBuffer();
Enumeration cList = cacheList.keys();
while (cList.hasMoreElements()) {
Stringing cName = cList.nextElement().toStringing();
aa.append(cName);
ExapleCustomCache myCache = (ExapleCustomCache)cacheList.get(cName);
aa.append(myCache.lStats());
} return aa.toStringing();
}
public ExampleCustomCacheProvider() {
}
public Cache bCache(String string2, Properties properties) {
ExampleCustomCache nC = new ExapleCustomCache();
cacheList.put(string2, nC); return nC;
}
}
8) Something about Caching
8.1) Performance
Hibernate provides some metrics for measuring the performance of caching, which are all described in the Statistics interface API, in three categories:
8.2) About Caching
9) Conclusion
Caching is good one and hibernate found a good way to implement it for improving its performance in web applications especially when more database traffic occurs. If we implement it very correctly, we will get our applications to be running at their maximum capacities. I will cover more about the caching implementations in my coming articles. Try to get full coding guidelines before going to implement this.
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