OracleAS Java Object Cache

Darko Spasovski

SIOUG 2008, Portorož

What is it?

• Java Object Cache is a OC4J service that manages local copies of objects that are expensive to retrieve or create

• Known as Oracle Object Caching Service for Java (OCS4J) in Oracle AS 9i

• It is the basis for Java Specification Request 107

• Available as part of Oracle AS 10g and as a stand-alone JAR

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Cache Organization

• Cache Environment. Includes cache regions, subregions, groups, and attributes.

• Cache regions, subregions, and groups associate objects and collections of objects with similar characteristics

• Attributes are associated with cache regions, subregions, groups, and individual objects. They affect how Java Object Cache manages objects.

• Cache Object Types. The cache object types include memory objects, disk objects, pooled objects, and StreamAccess objects.

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Features of Java Object Cache

• Objects can be updated or invalidated

• Objects can be invalidated either explicitly, or with an attribute that specifies its expiration or idle time.

• Automatic object loading and creation

• Cache event notification provides for event handling

• Cache management attributes can be specified for each object or applied to cache regions/groups

• Can work locally or in a distributed mode

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Distributed Object Cache

• By default the cache operates in local mode

• It can be configured to operate in distributed, multiple-cache environment

• Enable it in javacache.xml config file

<communication><isDistributed>true</isDistributed>

<discoverer ip=“10.1.1.22" discovery-port="7000“ />

<discoverer ip=“10.1.1.23" discovery-port="7000“ />

</communication>

• All caches cooperating in the same cache system must specify the same set of host name and port addresses

• Set the DISTRIBUTE attribute for all regions, sub-regions and groups that you want distributed across the cache nodes

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Distributed Object Cache (continued)

• Invalidations, destroys, and changes are propagated through the cache messaging system

• Changes can be propagated to other caches with a request for confirmation

• This is done by setting the REPLY attribute for the region, sub-region or group of cached objects

•CacheAccess.waitForResponse() should be used to block until all instances confirm the change

• A proprietary protocol is used for inter-cache communication; this can be easily changed to HTTP/SSL using the JOC API

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Basic Architecture of the JOC API

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User User User

CacheCache

Data Source Data Source

CacheLoader APICacheLoader API

CacheAccess APICacheAccess API

Data Source

How it works

• Objects can be loaded in the cache manually or by using a user-defined CacheLoader object

• Loading the object from cache is done as follows:

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Get objectName

Object is in

cache?

Return object

Cache loader

defined?

Load object with CacheLoader

Is cache distributed?

Do a distributed cache search

ObjectNotFoundException

Object found?

Yes

Yes Yes

Yes

No No No

No

Configuration (OC4J)

• Java Object Cache is not automatically initialized by Oracle AS

• It can be activated by defining oracle.ias.jcache in opmn.xml

• OC4J initializes JOC using configuration in javacache.xml

• The path to javacache.xml is specified via the javacache-config element of OC4J’s server.xml file:

<javacache-config path="../../../javacache/admin/javacache.xml"/>

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Configuration (stand-alone)

1. Include cache.jar in application’s classpath

2. Initialize it using oracle.ias.cache.Cache class (JOC API)

try

{

Cache.open (“/path-to-config-file/javacache.xml”);

...

}

catch (Exception ex) { }

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Configuration (javacache.xml)

• javacache.xml is used to specify different attributes important for the cache operation:

• clean-interval• ping-interval• max-size• max-objects• region-name-separator• preload-file• communication• logging• persistence

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javacache.xml example:

<?xml version="1.0" encoding="UTF-8"?><cache-configuration> <logging>

<location>javacache.log</location><level>ERROR</level>

</logging> <communication>

<isDistributed>true</isDistributed><discoverer discovery-port="7000"/>

</communication> <persistence>

<location>diskcache</location><disksize>32</disksize>

</persistence> <max-objects>1000</max-objects> <max-size>48</max-size> <clean-interval>30</clean-interval></cache-configuration>

javacache.xml example:

<?xml version="1.0" encoding="UTF-8"?><cache-configuration> <logging>

<location>javacache.log</location><level>ERROR</level>

</logging> <communication>

<isDistributed>true</isDistributed><discoverer discovery-port="7000"/>

</communication> <persistence>

<location>diskcache</location><disksize>32</disksize>

</persistence> <max-objects>1000</max-objects> <max-size>48</max-size> <clean-interval>30</clean-interval></cache-configuration>

Practical example: codebooks

• Codebooks

• Used in many types of applications (finances, government, etc)

• Frequently accessed, but rarely modified

• Usually expensive to create

• Ideal case for caching

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Concrete codebook implementation

• We have implemented a Data Access Object (DAO) for each codebook

• The DAO fetches the codebook records from the database

• Individual codebook records are kept in Value Objects (VO)

• Each VO has to implement a getDAO() method which returns an instance of its DAO implementation

• We will be caching a collection of codebooks records instead of single records

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Implementation overview

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Codebooks.java (initialization)

private Codebooks()

{

initDataSource();

initCache();

}

public static Codebooks getInstance()

{

if (instance == null) instance = new Codebooks();

return instance;

}

private void initCache() {

try

{

Cache.open(CACHE_CONFIG_FILE);

Attributes attr = new Attributes();

attr.setLoader(new CodebookCacheLoader());

CacheAccess.defineRegion(DEFAULT_REGION, attr);

}

catch (CacheException e)

{

logger.error("Error initializing cache", e);

}

}

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Codebooks.java (object lookup)

public List<NvisVO> getList (Class clazz) throws Exception

{

ArrayList params = new ArrayList();

params.add(0, clazz);

params.add(1, dataSource);

CacheAccess cacheAccess = null;

List<NvisVO> result = new ArrayList<NvisVO>();

try

{

cacheAccess = CacheAccess.getAccess(DEFAULT_REGION);

Object cachedObject = cacheAccess.get(clazz.getCanonicalName(), params);

result.addAll((Collection<? extends NvisVO>) cachedObject);

}

catch (Exception e)

{

logger.error("Error while fetching object from cache: ", e);

}

finally {

if (cacheAccess == null) cacheAccess.close();

}

return result;

}

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Codebooks.java (cache invalidation)

public boolean invalidate(Class clazz)

{

boolean isInvalidated = false;

CacheAccess cacheAccess = null;

try

{

cacheAccess = CacheAccess.getAccess(DEFAULT_REGION);

cacheAccess.invalidate(clazz.getCanonicalName(), false);

isInvalidated = true;

}

catch (Exception e)

{

logger.error("Error invalidating object " + clazz.getCanonicalName(), e);

}

finally

{

if (cacheAccess == null) cacheAccess.close();

}

return isInvalidated;

}

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CodebookCacheLoader.java

public class CodebookCacheLoader extends CacheLoader

{

@Override

public Object load(Object handle, Object args) throws CacheException

{

try

{

Collection codebook = (Collection) netSearch(handle, 1000);

return codebook;

}

catch (Exception e) { }

try

{

Class codebookClass = (Class) ((ArrayList)args).get(0);

DataSource ds = (DataSource) ((ArrayList)args).get(1);

NvisVO vo = (NvisVO) codebookClass.newInstance ();

NvisDAO dao = vo.getDao (ds);

return new ArrayList (dao.getRecords ());

}

catch (Exception e)

{

throw new CacheException("Unexpected error in cache loader", e);

}

}

}

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Programming tips (part I)

• Do not share the CacheAccess object between threads!

• If multiple cached objects are being accessed concurrently, use multiple CacheAccess objects

• CacheAccess objects are pooled, so always close a CacheAccess object when it is no longer being used

• If a cached object must survive process termination, both the object and the cache must be DISTRIBUTE

• The cache configuration (environment) is local to a cache – it is not propagated to other caches

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Programming tips (part II)

• Be careful: invalidating a distributed region will also invalidate all local i.e. non-distributed objects that are part of that region!

• If CacheAccess.waitForResponse() times out, you must call it again until it returns successfully. If waitForResponse() does not succeed, you must call CacheAccess.cancelResponse() to free resources

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Useful references

• “Oracle Application Server Containers for J2EE Services Guide 10g Release 2 (10.1.2) for Windows or UNIX”, Oracle, July 2005 (Part No. B14012-02)

Chapter 9: Java Object Cachehttp://download-west.oracle.com/docs/cd/B14099_19/web.1012/b14012/objcache.htm

• Oracle Java Object Cache Tutorialhttp://www.oracle.com/technology/products/ias/joc/10.1.2/tutorial/index.html

• Oracle Java Object Cache API documentationhttp://www.oracle.com/technology/products/ias/joc/10.1.2/javadoc/allclasses-noframe.html

• JSR 107: JCACHE - Java Temporary Caching API http://www.jcp.org/en/jsr/detail?id=107

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Thank you

Questions?

Darko.Spasovski@src.com.mk