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HIBERNATE - Relational Persistence for Idiomatic Java

Using JBoss Cache as a Hibernate Second Level Cache

3.5.0.alpha1

Copyright © 2009 Red Hat, Inc.

Legal Notice
Preface
1. Introduction
1.1. Overview
1.2. Requirements
1.2.1. Dependencies
1.2.2. JTA Transactional Support
1.3. Configuration Basics
2. Core Concepts
2.1. Types of Cached Data
2.1.1. Entities
2.1.2. Collections
2.1.3. Queries
2.1.4. Timestamps
2.2. Key JBoss Cache Behaviors
2.2.1. Replication vs. Invalidation vs. Local Mode
2.2.2. Synchronous vs. Asynchronous
2.2.3. Locking Scheme
2.2.4. Isolation Level
2.2.5. Initial State Transfer
2.2.6. Cache Eviction
2.2.7. Buddy Replication and Cache Loading
2.3. Matching JBC Behavior to Types of Data
2.3.1. The RegionFactory Interface
2.3.2. The CacheManager API
2.3.3. Sharable JGroups Resources
2.3.4. Bringing It All Together
3. Configuration
3.1. Configuring the Hibernate Session Factory
3.1.1. Basics
3.1.2. Specifying the RegionFactory Implementation
3.1.3. The SharedJBossCacheRegionFactory
3.1.4. The JndiSharedJBossCacheRegionFactory
3.1.5. The MultiplexedJBossCacheRegionFactory
3.1.6. The JndiMultiplexedJBossCacheRegionFactory
3.1.7. Legacy Configuration Properties
3.2. Configuring JBoss Cache
3.2.1. Configuring a Single Standalone Cache
3.2.2. Managing Multiple Caches via a CacheManager
3.2.3. JBoss Cache Configuration Details
3.2.4. Standard JBoss Cache Configurations
3.3. JGroups Configuration
3.3.1. Transport -- UDP vs. TCP
3.3.2. Standard JGroups Configurations
4. Cache Eviction
4.1. Overview
4.1.1. The Eviction Process
4.1.2. Eviction Regions
4.1.3. Eviction Policies
4.2. Organization of Data in the Cache
4.2.1. Region Prefix and Region Name
4.2.2. Entities
4.2.3. Collections
4.2.4. Queries
4.2.5. Timestamps
4.3. Example Configuration
4.4. Best Practices
5. Architecture
5.1. Hibernate Interface to the Caching Subsystem
5.2. Single JBoss Cache Instance Architecture
5.3. Multiple JBoss Cache Instance Architecture

Preface

This document is focused on the use of the JBoss Cache clustered transactional caching library as a tool for caching data in a Hibernate-based application.

Working with object-oriented software and a relational database can be cumbersome and time consuming in today's enterprise environments. Hibernate is an object/relational mapping tool for Java environments. The term object/relational mapping (ORM) refers to the technique of mapping a data representation from an object model to a relational data model with a SQL-based schema.

Hibernate not only takes care of the mapping from Java classes to database tables (and from Java data types to SQL data types), but also provides data query and retrieval facilities and can significantly reduce development time otherwise spent with manual data handling in SQL and JDBC.

In any application that works with a relational database, caching data retrieved from the database can potentially improve application performance. Hibernate provides a number of facilities for caching data on the database client side, i.e. in the Java process in which Hibernate is running. The primary facility is the Hibernate Session itself, which maintains a transaction-scoped cache of persistent data. If you wish to cache data beyond the scope of a transaction, it is possible to configure a cluster or JVM-level (technically a SessionFactory-level) cache on a class-by-class, collection-by-collection and query-by-query basis. This type of cache is referred to as a Second Level Cache.

Hibernate provides a pluggable architecture for implementing its Second Level Cache, allowing it to integrate with a number of third-party caching libraries. This document is focused on the use of the JBoss Cache clustered transactional caching library as an implementation of the Second Level Cache. It specifically focuses on JBoss Cache 3.

If you are new to Hibernate and Object/Relational Mapping or even Java, please follow these steps:

  1. Read the Hibernate Reference Documentation, particularly the Introduction and Architecture sections.

  2. Have a look at the eg/ directory in the Hibernate distribution, it contains a simple standalone application. Copy your JDBC driver to the lib/ directory and edit etc/hibernate.properties, specifying correct values for your database. From a command prompt in the distribution directory, type ant eg (using Ant), or under Windows, type build eg.

  3. Use the Hibernate Reference Documentation as your primary source of information. Consider reading Java Persistence with Hibernate (http://www.manning.com/bauer2) if you need more help with application design or if you prefer a step-by-step tutorial. Also visit http://caveatemptor.hibernate.org and download the example application for Java Persistence with Hibernate.

  4. FAQs are answered on the Hibernate website.

  5. Third party demos, examples, and tutorials are linked on the Hibernate website.

  6. The Community Area on the Hibernate website is a good resource for design patterns and various integration solutions (Tomcat, JBoss AS, Struts, EJB, etc.).

If you are new to the Hibernate Second Level Cache or to JBoss Cache, please follow these steps:

  1. Read the Hibernate Reference Documentation, particularly the Second Level Cache and Configuration sections.

  2. Read the JBoss Cache User Guide, Core Edition.

  3. Use this guide as your primary source of information on the usage of JBoss Cache 3 as a Hibernate Second Level Cache.

If you have questions, use the user forum linked on the Hibernate website. The user forum on the JBoss Cache website is also useful. We also provide a JIRA issue tracking system for bug reports and feature requests. If you are interested in the development of Hibernate, join the developer mailing list. If you are interested in translating this documentation into your language, contact us on the developer mailing list.

Commercial development support, production support, and training for Hibernate is available through Red Hat, Inc. (see http://www.hibernate.org/SupportTraining/). Hibernate is a Professional Open Source project and a critical component of the JBoss Enterprise Application Platform.

Chapter 1. Introduction

1.1. Overview
1.2. Requirements
1.2.1. Dependencies
1.2.2. JTA Transactional Support
1.3. Configuration Basics

JBoss Cache is a tree-structured, clustered, transactional cache. It includes support for maintaining cache consistency across multiple cache instances running in a cluster. It integrates with JTA transaction managers, supporting transaction-scoped locking of cache elements and automatic rollback of cache changes upon transaction rollback. It supports both pessimistic and optimistic locking, with the tree-structure of the cache allowing maximum concurrency.

All of these features make JBoss Cache an excellent choice for use as a Hibernate Second Level Cache, particularly in a clustered environment. A Hibernate Session is a transaction-scoped cache of persistent data -- data accessed via the Session is cached in the Session for the duration of the current transaction, and then is cleared. A Second Level Cache is an optional cluster or JVM-level cache whose contents are maintained beyond the life of a transaction and whose contents can be shared across transactions. Use of a Second Level Cache is configured as part of the configuration of the Hibernate SessionFactory. If a Second Level Cache is enabled, caching of an instance of a particular entity class or of results of a particular query can be configured on a class-by-class, collection-by-collection and query-by-query basis. See the Hibernate Reference Documentation for more on Second Level Cache basics and how to configure entity classes, collections and queries for caching.

The JBoss Cache Second Level Cache integration supports the transactional and read only cache concurrency strategies discussed in the Hibernate Reference Documentation. It supports query caching and is, of course, cluster safe.

Second level caching with JBoss Cache 3 requires the use of JBoss Cache 3.1.0 or later. The core JBoss Cache project is used; the related POJO Cache project/library is not needed. The following jars, included with the JBoss Cache distribution, need to be on the classpath:

JBoss Cache also needs to have the classes in the javax.transaction package on the classpath, but those are already included in the Hibernate distribution.

The hibernate-jbosscache.jar that is included with the Hibernate distribution also needs to be on the classpath.

A JBoss Cache configuration file, and usually a JGroups configuration file[1], need to be on the classpath. The hibernate-jbosscache.jar includes standard configuration files in the org.hibernate.cache.jbc.builder package. The jbc-configs.xml file is for JBoss Cache and the jgroups-stacks.xml file is for JGroups. See Section 3.2, “Configuring JBoss Cache” and Section 3.3, “JGroups Configuration” for more details on these files. Users can create their own versions and tell the SessionFactory to use them; see Section 3.1, “Configuring the Hibernate Session Factory” for details.

JBoss Cache requires integration with a JTA TransactionManager in order to meet the requirements of the second level caching use case. This means your Hibernate application must be configured to use JTA:

See the Hibernate Reference Documentation for an in-depth discussion of using Hibernate with JTA

The key steps in using JBoss Cache as a second level cache are to:

See Chapter 3, Configuration for full details on configuration.


[1] JGroups is the group communication library used by JBoss Cache for intra-cluster communication.

Chapter 2. Core Concepts

2.1. Types of Cached Data
2.1.1. Entities
2.1.2. Collections
2.1.3. Queries
2.1.4. Timestamps
2.2. Key JBoss Cache Behaviors
2.2.1. Replication vs. Invalidation vs. Local Mode
2.2.2. Synchronous vs. Asynchronous
2.2.3. Locking Scheme
2.2.4. Isolation Level
2.2.5. Initial State Transfer
2.2.6. Cache Eviction
2.2.7. Buddy Replication and Cache Loading
2.3. Matching JBC Behavior to Types of Data
2.3.1. The RegionFactory Interface
2.3.2. The CacheManager API
2.3.3. Sharable JGroups Resources
2.3.4. Bringing It All Together

This chapter focuses on some of the core concepts underlying how the JBoss Cache-based implementation of the Hibernate Second Level Cache works. There's a fair amount of detail, which certainly doesn't all need to be mastered to use JBoss Cache with Hibernate. But, an understanding of some of the basic concepts here will help a user understand what some of the typical configurations discussed in the next chapter are all about.

If you want to skip the details for now, feel free to jump ahead to Section 2.3.4, “Bringing It All Together”

The Second Level Cache can cache four different types of data: entities, collections, query results and timestamps. Proper handling of each of the types requires slightly different caching semantics. A major improvement in Hibernate 3.3 was the addition of the org.hibernate.cache.RegionFactory SPI, which allows Hibernate to tell the caching integration layer what type of data is being cached. Based on that knowledge, the cache integration layer can apply the semantics appropriate to that type.

Entities are the most common type of data cached in the second level cache. Entity caching requires the following semantics in a clustered cache:

Collection caching refers to the case where a cached entity has as one of its fields a collection of other entities. Hibernate handles this field specially in the second level cache; a special area in the cache is created where the primary keys of the entities in the collection are stored.

The management of collection caching is very similar to entity caching, with a few differences:

In essence, for collections Hibernate only supports cache reads and the put operation, with any modification of the collection resulting in cluster-wide invalidation of that collection from the cache. If the collection field is accessed again, a new read from the database will be done, followed by another cache put.

Hibernate supports caching of query results in the second level cache. The HQL statement that comprised the query is cached (including any parameter values) along with the primary keys of all entities that comprise the result set.

The semantics of query caching are significantly different from those of entity caching. A database row that reflects an entity's state can be locked, with cache updates applied with that lock in place. The semantics of entity caching take advantage of this fact to help ensure cache consistency across the cluster. There is no clear database analogue to a query result set that can be efficiently locked to ensure consistency in the cache. As a result, the fail-fast semantics used with the entity caching put operation are not available; instead query caching has semantics akin to an entity insert, including costly synchronous cluster updates and the JBoss Cache two phase commit protocol. Furthermore, Hibernate must agressively invalidate query results from the cache any time any instance of one of the entity classes involved in the query's WHERE clause changes. All such query results are invalidated, even if the change made to the entity instance would not have affected the query result. It is not performant for Hibernate to try to determine if the entity change would have affected the query result, so the safe choice is to invalidate the query. See Section 2.1.4, “Timestamps” for more on query invalidation.

The effect of all this is that query caching is less likely to provide a performance boost than entity/collection caching. Use it with care and benchmark your application with it enabled and disabled. Be careful about replicating query results; caching them locally only on the node that executed the query will be more performant unless the query is quite expensive, is very likely to be repeated on other nodes, and is unlikely to be invalidated out of the cache.[2].

The JBoss Cache-based implementation of query caching adds a couple of interesting semantics, both designed to ensure that query cache operations don't block transactions from proceeding:

  • The insertion of a query result into the cache is very much like the insertion of a new entity. The difference is it is possible for two transactions, possibly on different nodes, to try to insert the same query at the same time. (If this happened with entities, the database would throw an exception with a primary key violation before any caching work could start). This could lead to long delays as the transactions compete for cache locks. To prevent such delays, the cache integration layer will set a very short (a few ms) lock timeout before attempting to cache a query result. If there is any sort of locking conflict, it will be detected quickly, and the attempt to cache the result will be quietly abandonded.

  • A read of a query result does not result in any long-lasting read lock in the cache. Thus, the fact that an uncommitted transaction had read a query result does not prevent concurrent transactions from subsequently invalidating that result and caching a new result set. However, an insertion of a query result into the cache will result in an exclusive write lock that lasts until the transaction that did the insert commits; this lock will prevent other transactions from reading the result. Since the point of query caching is to improve performance, blocking on a cache read for an extended period seems suboptimal. So, the cache integration code will set a very low lock acquisition timeout before attempting the read; if there is a lock conflict, the read will silently fail, resulting in a cache miss and a re-execution of the query against the database.

Timestamp caching is an internal detail of query caching. As part of each query result, Hibernate stores the timestamp of when the query was executed. There is also a special area in the cache (the timestamps cache) where, for each entity class, the timestamp of the last update to any instance of that class is stored. When a query result is read from the cache, its timestamp is compared to the timestamps of all entities involved in the query. If any entity has a later timestamp, the cached result is discarded and a new query against the database is executed.

The semantics of of the timestamp cache are quite different from those of the entity, collection and query caches.

JBoss Cache is a very flexible tool and includes a great number of configuration options. See the JBoss Cache User Guide for an in depth discussion of these options. Here we focus on the main concepts that are most important to the Second Level Cache use case. This discussion will focus on concepts; see Section 3.2, “Configuring JBoss Cache” for details on the actual configurations involved.

JBoss Cache provides three different choices for how a node in the cluster should interact with the rest of the cluster when its local state is updated:

In JBoss Cache terms, synchronous vs. asynchronous refers to whether a thread that initiates a cluster-wide message blocks until that message has been received, processed and acknowledged by the other members of the cluster. Synchronous means the thread blocks; asynchronous means the message is sent and the thread immediately returns; more of a "fire and forget". An example of a message would be a set of cache inserts, updates and removes sent out to the cluster as part of a transaction commit.

In almost all cases, the cache should be configured to use synchronous messages, as these are the only way to ensure data consistency across the cluster. JBoss Cache supports programatically overriding the default configured behavior on a per-call basis, so for the special cases where sending a message asynchronously is appropriate, the Hibernate/JBoss Cache integration code will force the call to go asynchronously. So, configure your caches to use synchronous messages.

JBoss Cache supports both MVCC and pessimistic locking schemes. See the JBoss Cache User Guide for an in depth discussion of these options. In the Second Level Cache use case, the main benefit of MVCC locking is that updates of cached entities by one transaction do not block reads of the cached entity by other transactions, yet REPEATABLE_READ semantics are preserved. MVCC is also significantly faster than pessimistic locking. For these reasons, using MVCC locking is recommended for Second Level Caches.

Optimistic Locking

JBoss Cache supports a third locking scheme, known as Optimistic locking. Like MVCC, optimistic locking does not block readers for writes, yet preserves REPEATABLE_READ semantics. However, the runtime overhead of optimistic locking is much, much higher than that of MVCC. So, use of MVCC is recommended.

If the MVCC or PESSIMISTIC node locking schemes are used, JBoss Cache supports different isolation level configurations that specify how different transactions coordinate the locking of nodes in the cache: READ_COMMITTED and REPEATABLE_READ. These are somewhat analogous to database isolation levels; see the JBoss Cache User Guide for an in depth discussion of these options. In both cases, cache reads do not block for other reads. In both cases a transaction that writes to a node in the cache tree will hold an exclusive lock on that node until the transaction commits, causing other transactions that wish to read the node to block. In the REPEATABLE_READ case, the read lock held by an uncommitted transaction that has read a node will cause another transaction wishing to write to that node to block until the read transaction commits. This ensures the reader transaction can read the node again and get the same results, i.e. have a repeatable read.

READ_COMMITTED allows the greatest concurrency, since reads don't block each other and also don't block a write.

If the deprecated OPTIMISTIC node locking scheme is used, any isolation level configuration is ignored by the cache. Optimistic locking provides a repeatable read semantic but does not cause writes to block for reads.

In most cases, a REPEATABLE_READ setting on the cache is not needed, even if the application wants repeatable read semantics. This is because the Second Level Cache is just that -- a secondary cache. The primary cache for an entity or collection is the Hibernate Session object itself. Once an entity or collection is read from the second level cache, it is cached in the Session for the life of the transaction. Subsequent reads of that entity/collection will be resolved from the Session cache itself -- there will be no repeated read of the Second Level Cache by that transaction. So, there is no benefit to a REPEATABLE_READ configuration in the Second Level Cache.

The only exception to this is if the application uses Session's evict() or clear() methods to remove data from the Session cache and during the course of the same transaction wants to read that same data again with a repeatable read semantic.

Note that for query and timestamp caches, the behavior of the Hibernate/JBC integration will not allow repeatable read semantics even if JBC is configured for REPEATABLE_READ. A cache read will not result in a read lock in the cache being held for the life of the transaction. So, for these caches there is no benefit to a REPEATABLE_READ configuration.

When a new node joins a running cluster, it can request from an existing member a copy of that member's current cache contents. This process is known as an initial state transfer. Doing an initial state transfer allows the new member to have a "hot cache"; i.e. as user requests come in, data will already be cached, helping avoid an initial set of reads from the database.

However, doing an initial state transfer comes at a cost. The node providing the state needs to lock its entire tree, serialize it and send it over the network. This could be a large amount of data and the transfer could take a considerable period of time to process. While the transfer is ongoing, the state provider is holding locks on its cache, preventing any local or replicated updates from proceeeding. All work around the cache can come to a halt for a period.

Because of this cost, we generally recommend avoiding initial state transfers in the second level cache use case. The exception to this is the timestamps cache. For the timestamps cache, an initial state transfer is required.

Eviction refers to the process by which old, relatively unused, or excessively voluminous data can be dropped from the cache, allowing the cache to remain within a memory budget. Generally, applications that use the Second Level Cache should configure eviction. See Chapter 4, Cache Eviction for details.

Buddy replication refers to a JBoss Cache feature whereby each node in the cluster replicates its cached data to a limited number (often one) of "buddies" rather than to all nodes in the cluster. Buddy replication should not be used in a Second Level Cache. It is intended for use cases where one node in the cluster "owns" some data , and just wants to make a backup copy of the data to provide high availability. The data (e.g. a web session) is never meant to be accessed simultaneously on two different nodes in the cluster. Second Level Cache data does not meet this "ownership" criteria; entities are meant to be simultaneously usable by all nodes in the cluster.

Cache Loading refers to a JBoss Cache feature whereby cached data can be persisted to disk. The persisted data either serves as a highly available copy of the data in case of a cluster restart, or as an overflow area for when the amount of cached data exceeds an application's memory budget. Cache loading should not be used in a Second Level Cache. The underlying database from which the cached data comes already serves the same functions; adding a cache loader to the mix is just wasteful.

The preceding discussion has gone into a lot of detail about what Hibernate wants to accomplish as it caches data, and what JBoss Cache configuration options are available. What should be clear is that the configurations that are best for caching one type of data are not the best (and are sometimes completely incorrect) for other types. Entities likely work best with synchronous invalidation; timestamps require replication; query caching might do best in local mode.

Prior to Hibernate 3.3 and JBoss Cache 2.1, the conflicting requirements between the different cache types led to a real dilemna, particularly if query caching was enabled. This conflict arose because all four cache types needed to share a single underlying cache, with a single configuration. If query caching was enabled, the requirements of the timestamps cache basically forced use of synchronous replication, which is the worst performing choice for the more critical entity cache and is often inappropriate for the query cache.

With Hibernate 3.3 and JBoss Cache 2.1 it has become possible, even easy, to use separate underlying JBoss Cache instances for the different cache types. As a result, the entity cache can be optimally configured for entities while the necessary configuration for the timestamps cache is maintained.

There were three key changes that make this improvement possible:

As mentioned previously, Hibernate 3.3 introduced the RegionFactory SPI as its mechanism for managing the Second Level Cache. This SPI makes it possible for implementations to know at all times whether they are working with entities, collections, queries or timestamps. That knowledge allows the Hibernate/JBoss Cache integration layer to make the best use of the various options JBoss Cache provides.

A Hibernate user doesn't need to understand the RegionFactory SPI in any detail at all; the main point is internally it makes possible independent management of the different cache types.

The CacheManager API is a new feature of JBoss Cache 2.1. It provides an API for managing multiple distinct JBoss Cache instances in the same VM. Basically a CacheManager is instantiated and provided a set of named cache configurations. An application like the Hibernate/JBoss Cache integration layer accesses the CacheManager and asks for a cache configured with a particular named configuration.

Again,a Hibernate user doesn't need to understand the CacheManager; it's an internal detail. The thing to understand is that the task of a Hibernate Second Level Cache user is to:

See Chapter 3, Configuration for more on how to do this.

JGroups is the group communication library JBoss Cache uses JGroups to send messages around a cluster. Each cache has a JGroups Channel; different channels around the cluster that have the same name and compatible configurations detect each other and form a group for message transmission.

A Channel is a fairly heavy object, typically using a good number of threads, several sockets and some good sized network I/O buffers. Creating multiple different channels in the same VM was therefore costly, and was an administrative burden as well, since each channel would need separate configuration to use different network addresses or ports. Architecturally, this mitigated against having multiple JBoss Cache instances in an application, since each would need its own Channel.

Added in JGroups 2.5 and much improved in the JGroups 2.6 series is the concept of sharable JGroups resources. Basically, the heavyweight JGroups elements can be shared. An application (e.g. the Hibernate/JBoss Cache integration layer) uses a JGroups ChannelFactory. The ChannelFactory is provided with a set of named channel configurations. When a Channel is needed (e.g. by a JBoss Cache instance), the application asks the ChannelFactory for the channel by name. If different callers ask for a channel with the same name, the ChannelFactory ensures that they get channels that share resources.

The effect of all this is that if a user wants to use four separate JBoss Cache instances, one for entity caching, one for collection caching, one for query caching and one for timestamp caching, those four caches can all share the same underlying JGroups resources.

The task of a Hibernate Second Level Cache user is to:

See Section 3.3, “JGroups Configuration” for more on JGroups.

So, we've seen that Hibernate caches up to four different types of data (entities, collections, queries and timestamps) and that Hibernate + JBoss Cache gives you the flexibility to use a separate underlying JBoss Cache, with different behavior, for each type. You can actually deploy four separate caches, one for each type.

In practice, four separate caches are unnecessary. For example, entities and collection caching have similar enough semantics that there is no reason not to share a JBoss Cache instance between them. The queries can usually use the same cache as well. Similarly, queries and timestamps can share a JBoss Cache instance configured for replication, with the hibernate.cache.jbc.query.localonly=true configuration letting you turn off replication for the queries if you want to.

Here's a decision tree you can follow:

  1. Decide if you want to enable query caching.

  2. Decide if you want to use invalidation or replication for your entities and collections. Invalidation is generally recommended for entities and collections.

  3. If you are using query caching, from the above decision tree you've either got your timestamps sharing a cache with other data types, or they are by themselves. Either way, the cache being used for timestamps must have initial state transfer enabled. Now, if the timestamps are sharing a cache with entities, collections or queries, decide whether you want initial state transfer for that other data. See Section 2.2.5, “Initial State Transfer” for the implications of this. If you don't want initial state transfer for the other data, you'll need to have a separate cache for the timestamps.

  4. Finally, if your queries are sharing a cache configured for replication, decide if you want the cached query results to replicate. (The timestamps cache must replicate.) If not, you'll want to set the hibernate.cache.region.jbc2.query.localonly=true option when you configure your SessionFactory

Once you've made these decisions, you know whether you need just one underlying JBoss Cache instance, or more than one. Next we'll see how to actually configure the setup you've selected.


[2] See the discussion of the hibernate.cache.jbc.query.localonly property in Section 3.1, “Configuring the Hibernate Session Factory”

for more on how to only cache query results locally.

Chapter 3. Configuration

3.1. Configuring the Hibernate Session Factory
3.1.1. Basics
3.1.2. Specifying the RegionFactory Implementation
3.1.3. The SharedJBossCacheRegionFactory
3.1.4. The JndiSharedJBossCacheRegionFactory
3.1.5. The MultiplexedJBossCacheRegionFactory
3.1.6. The JndiMultiplexedJBossCacheRegionFactory
3.1.7. Legacy Configuration Properties
3.2. Configuring JBoss Cache
3.2.1. Configuring a Single Standalone Cache
3.2.2. Managing Multiple Caches via a CacheManager
3.2.3. JBoss Cache Configuration Details
3.2.4. Standard JBoss Cache Configurations
3.3. JGroups Configuration
3.3.1. Transport -- UDP vs. TCP
3.3.2. Standard JGroups Configurations

There are three main areas of configuration involved in using JBoss Cache 3 for your Hibernate Second Level Cache: configuring the Hibernate SessionFactory, configuring the underlying JBoss Cache instance(s), and configuring the JGroups ChannelFactory. If you use the standard JBoss Cache and JGroups configurations that ship with the hibernate-jbosscache2.jar, then all you need to worry about is the SessionFactory configuration.

There are five basic steps to configuring the SessionFactory:

  • Make sure your Hibernate is configured to use JTA transactions. See Section 1.2.2, “JTA Transactional Support” for details.

  • Tell Hibernate you whether to enable caching of entities and collections. No need to set this property if you don't: 

    hibernate.cache.use_second_level_cache=true

  • Tell Hibernate you want to enable caching of query results. No need to set this property if you don't: 

    hibernate.cache.use_query_cache=true

  • If you have enabled caching of query results, tell Hibernate if you want to suppress costly replication of those results around the cluster. No need to set this property if you want query results replicated: 

    hibernate.cache.jbc.query.localonly=true

  • Finally, you need to tell Hibernate what RegionFactory implementation to use to manage your caches. You do this by setting the hibernate.cache.region.factory_class configuration option. 

    hibernate.cache.region.factory_class=
   org.hibernate.cache.jbc.MultiplexedJBossCacheRegionFactory

    To determine the correct factory class, you must decide whether you need just one underlying JBoss Cache instance to support the different types of caching you will be doing, or whether you need more than one. See Chapter 2, Core Concepts and particularly Section 2.3.4, “Bringing It All Together” for more on how to make that decision. Once you know the answer, see Section 3.1.2, “Specifying the RegionFactory Implementation” to find the factory class that best meets your needs.

    Once you've specified your factory class, there may be other factory-class-specific configurations you may want to set. The available options are explained below.

Hibernate 3.5 ships with the following RegionFactory implementations that work with JBoss Cache 3. Select the one that is appropriate to your needs and use it with the hibernate.cache.region.factory_class configuration option.

org.hibernate.cache.jbc.SharedJBossCacheRegionFactory

Instantiates a single JBoss Cache instance for use with all cache data types (entities, collections, queries, timestamps).

org.hibernate.cache.jbc.JndiSharedJBossCacheRegionFactory

Uses a single JBoss Cache instance for all cache data types. However, does not instantiate the JBoss Cache instance itself; instead looks for an existing cache in JNDI. This allows sharing of a single JBoss Cache instance across multiple Hibernate session factories running in the same environment.

org.hibernate.cache.jbc.MultiplexedJBossCacheRegionFactory

Supports using multiple JBoss Cache instances with different cache data types (entities, collections, queries, timestamps) assigned to different JBoss Cache instances. Instantiates a JBoss Cache CacheManager to manage the JBoss Cache instances.

org.hibernate.cache.jbc.JndiMultiplexedJBossCacheRegionFactory

Functions like JndiMultiplexedJBossCacheRegionFactory, but instead of instantiating its own CacheManager it looks for an existing one in JNDI. This allows sharing of the various JBoss Cache instances across multiple Hibernate session factories running in the same environment.

The SharedJBossCacheRegionFactory supports a number of additional configuration options:

hibernate.cache.jbc.cfg.shared

Classpath or filesystem resource containing JBoss Cache configuration settings the underlying cache should use. Default value is treecache.xml.

hibernate.cache.jbc.cfg.multiplexer.stacks

Classpath or filesystem resource containing JGroups protocol stack configurations the ChannelFactory should use. Default is org/hibernate/cache/jbc/builder/jgroups-stacks.xml, a file found in the hibernate-jbosscache.jar.

Note that the default treecache.xml file does not exist; it is up to the user to provide it.

The JndiSharedJBossCacheRegionFactory supports an additional configuration option:

hibernate.cache.jbc.cfg.shared

Specifies the JNDI name under which the JBoss Cache instance to use is bound. Note that although this configuration property has the same name as the one used by SharedJBossCacheRegionFactory, the meaning here is different. Note also that in this class' usage of the property, there is no default value -- the user must specify the property.

The JndiSharedJBossCacheRegionFactory requires that the JBoss Cache instance is already bound in JNDI; it will not create and bind one if it isn't. It is up to the the user to ensure the cache is created and bound in JNDI before the Hibernate SessionFactory is created.

The MultiplexedJBossCacheRegionFactory supports a number of additional configuration options:

hibernate.cache.jbc.configs

Classpath or filesystem resource containing JBoss Cache configurations the CacheManager should use. Default is org/hibernate/cache/jbc2/builder/jbc2-configs.xml, a file found in the hibernate-jbosscache2.jar.

hibernate.cache.jbc.cfg.multiplexer.stacks

Classpath or filesystem resource containing JGroups protocol stack configurations the ChannelFactory should use. Default is org/hibernate/cache/jbc/builder/jgroups-stacks.xml, a file found in the hibernate-jbosscache.jar.

hibernate.cache.jbc.cfg.entity

Name of the configuration that should be used for entity caches. Default value is mvcc-entity.

hibernate.cache.jbc.cfg.collection

Name of the configuration that should be used for collection caches. No default value, as by default we try to use the same JBoss Cache instance that is used for entity caching.

hibernate.cache.jbc.cfg.timestamps

Name of the configuration that should be used for timestamp caches. Default value is timestamps-cache.

hibernate.cache.jbc.cfg.query

Name of the configuration that should be used for query caches. By default, tries to use the same cache as is used for entity caching. If there is no entity cache, the default value is local-query.

Many of the default values name JBoss Cache configurations in the standard jbc-configs.xml file found in the hibernate-jbosscache.jar. See Section 3.2.4, “Standard JBoss Cache Configurations” for details on those configurations. If you want to set hibernate.cache.jbc.configs and use your own JBoss Cache configuration file, you can still take advantage of these default names; just name the configurations in your file to match.

This is all looks a bit complex, so let's show what happens if you just configure the defaults, with query caching enabled: 

hibernate.cache.use_second_level_cache=true
hibernate.cache.use_query_cache=true
hibernate.cache.region.factory_class=
   org.hibernate.cache.jbc.MultiplexedJBossCacheRegionFactory

You would end up using two JBoss Cache instances:

  • One, for the entities, collection and queries, would use the optimistic-entity configuration. This cache would use optimistic locking, synchronous invalidation and would disable initial state transfer.

  • The second, for timestamps, would use the timestamps-cache configuration. This cache would use pessimistic locking, asynchronous replication and would enable initial state transfer.

See Section 3.2.4, “Standard JBoss Cache Configurations” for more on these standard cache configurations.

If you hadn't set hibernate.cache.use_query_cache=true you'd just have the single optimistic-entity cache, shared by the entities and collections.

The JndiMultiplexedJBossCacheRegionFactory supports the following additional configuration options:

hibernate.cache.jbc.cachefactory

Specifies the JNDI name under which the CacheManager to use is bound. There is no default value -- the user must specify the property.

hibernate.cache.jbc.cfg.entity

Name of the configuration that should be used for entity caches. Default value is mvcc-entity.

hibernate.cache.jbc.cfg.collection

Name of the configuration that should be used for collection caches. No default value, as by default we try to use the same JBoss Cache instance that is used for entity caching.

hibernate.cache.jbc.cfg.timestamps

Name of the configuration that should be used for timestamp caches. Default value is timestamps-cache.

hibernate.cache.jbc.cfg.query

Name of the configuration that should be used for query caches. By default, tries to use the same cache as is used for entity caching. If there is no entity cache, the default value is local-query.

See Section 3.1.5, “The MultiplexedJBossCacheRegionFactory” for a discussion of how the various hibernate.cache.jbc.cfg options combine to determine what JBoss Cache instances are used.

The JndiMultiplexedJBossCacheRegionFactory requires that the JBoss Cache CacheManager is already bound in JNDI; it will not create and bind one if it isn't. It is up to the the user to ensure the cache is CacheManager and bound in JNDI before the Hibernate SessionFactory is created.

A number of the configuration properties discussed above have changed their name from Hibernate 3.3 to Hibernate 3.5. However, to aid users moving applications from 3.3 to 3.5, the legacy property names are still supported. The legacy property names are:

To understand the meaning of these legacy properties, just change .region.jbc2 to .jbc and see the documentation above. The only exception to that is hibernate.cache.region.jbc2.cfg.ts has been changed to hibernate.cache.jbc.cfg.timestamps.

JBoss Cache provides a great many different configuration options; here we are just going to look at a few that are most relevant to the Second Level Cache use case. Please see the JBoss Cache User Guide for full details.

To configure a single standalone cache (i.e. for use by a SharedJBossCacheRegionFactory), you need to create a standard JBoss Cache XML configuration file and place it on the classpath. See the JBoss Cache User Guide and the JBoss Cache distribution for examples of JBoss Cache configuration files.

If the resource path to your file is treecache.xml, the SharedJBossCacheRegionFactory will find it by default; otherwise you will need to use a configuration option to tell it where it is. See Section 3.1.3, “The SharedJBossCacheRegionFactory” for instruction on how to do that.

If you are using MultiplexedJBossCacheRegionFactory you will need to provide a set of JBoss Cache configurations for its CacheManager to use. (Or, use the set in the jbc-configs.xml file that ships with hibernate-jbosscache.jar.) The XML file used by a CacheManager is very similar to the usual config file used by a standalone cache; the biggest difference is it can include multiple, named, configurations. The format looks like this: 

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

<cache-configs>

    <!-- A config appropriate for entity/collection caching. -->
    <cache-config name="mvcc-entity">

        <!-- Node locking scheme -->
        <attribute name="NodeLockingScheme">MVCC</attribute> 
        
        ..... other configuration attributes
        
    </cache-config>


    <!-- A config appropriate for entity/collection caching that
         uses pessimistic locking -->
    <cache-config name="pessimistic-entity">

        <!-- Node locking scheme -->
        <attribute name="NodeLockingScheme">PESSIMISTIC</attribute>   
        
        ..... other configuration attributes
        
    </cache-config>
    
</cache-configs>

Each <cache-config> element contains a complete cache configuration, with the same contents as what you would place in the <mbean> element in a standalone cache configuration file. The name attribute on the <cache-config> element provides the identifier for the configuration; users of the CacheManager will provide this name when requesting a JBoss Cache instance that uses this configuration.

Let's look at how to specify a few of the JBoss Cache configuration options that are most relevant to the Hibernate use case.

The JBoss Cache CacheMode attribute encapsulates whether the cache uses replication, invalidation or local mode, as well as whether messages should be synchronous or asynchronous. See Section 2.2.1, “Replication vs. Invalidation vs. Local Mode” and Section 2.2.2, “Synchronous vs. Asynchronous” for a discussion of these concepts.

The CacheMode is configured as follows: 

<!-- Legal modes are LOCAL
                     REPL_ASYNC
                     REPL_SYNC
                     INVALIDATION_ASYNC
                     INVALIDATION_SYNC
-->
<attribute name="CacheMode">INVALIDATION_SYNC</attribute>

The JBoss Cache NodeLockingScheme attribute configures whether optimistic locking or pessimistic locking should be used. See Section 2.2.3, “Locking Scheme” for a discussion of locking.

The NodeLockingScheme is configured as follows: 

<!-- Node locking scheme:
        MVCC
        PESSIMISTIC (default)
-->
<attribute name="NodeLockingScheme">MVCC</attribute>

The JBoss Cache IsolationLevel attribute configures whether READ_COMMITTED or REPEATABLE_READ semantics are needed if pessimistic locking is used. It has no effect if optimistic locking is used. See Section 2.2.4, “Isolation Level” for a discussion of isolation levels.

The IsolationLevel is configured as follows: 

<!-- Isolation level:
        READ_COMMITTED
        REPEATABLE_READ
-->
<attribute name="IsolationLevel">READ_COMMITTED</attribute>

Each JBoss Cache instance (except those with CacheMode LOCAL) will need a JGroups Channel. The cache configuration needs to tell JGroups how to set up the channel's protocol stack. This is configured as follows: 

<attribute name="MultiplexerStack">udp</attribute>

An alternate approach is to include the full protocol stack configuration in the JBoss Cache configuration: 

<!-- JGroups protocol stack properties. -->
<attribute name="ClusterConfig">
   <config>
      <UDP mcast_addr="228.10.10.10"
           mcast_port="45588"
           tos="8"  
           
           ... many more details
           
      <pbcast.STATE_TRANSFER/>
      <pbcast.FLUSH timeout="0"/>
   </config>
</attribute>

See Section 3.3, “JGroups Configuration” for more on JGroups configuration.

See Section 2.2.5, “Initial State Transfer” for a discussion of the concept of initial state transfer.

Initial State Transfer is configured as follows: 

<!-- Whether or not to fetch state on joining a cluster. -->
<attribute name="FetchInMemoryState">false</attribute>

JBoss Cache includes a feature called Region Based Marshalling that helps ensure the correct classloader is in place when objects are serialized and deserialized as part of replication and invalidation messages. This feature adds some overhead, but it allows your cache to work in complex classloading environments such as those found in many application servers. It can be disabled if your application meets the following criteria:

Region based marshalling is configured as follows: 

<!--
 Whether to use marshalling or not. Default is "false".
-->
<attribute name="UseRegionBasedMarshalling">true</attribute>
<!-- Must match the value of "UseRegionBasedMarshalling" -->
<attribute name="InactiveOnStartup">true</attribute>

Region based marshalling is enabled in the standard cache configurations that ship with hibernate-jbosscache.jar

This topic deserves a chapter of it's own. See Chapter 4, Cache Eviction.

Hibernate ships with a number of standard JBoss Cache configurations in the hibernate-jbosscache.jar's jbc-configs.xml file. The following table highlights the key features of each configuration.

Table 3.1. Standard JBoss Cache Configurations

NameValid ForOptimal ForCacheModeLockingState Transfer
mvcc-entity E/C/Q E/C/Q INVALIDATION_SYNC MVCC

no

optimistic-entity E/C/Q -- INVALIDATION_SYNC OPTIMISTIC

no

pessimistic-entity E/C/Q -- INVALIDATION_SYNC PESSIMISTIC

no

local-query Q Q LOCAL MVCC

no

replicated-query Q -- LOCAL MVCC

no

timestamps-cache T T REPL_ASYNC MVCC

yes

mvcc-shared E/C/Q/T -- REPL_SYNC MVCC

yes

optimistic-shared E/C/Q/T -- REPL_SYNC OPTIMISTIC

yes

pessimistic-shared E/C/Q/T -- REPL_SYNC PESSIMISTIC

yes


A few notes on the above table:

These standard configurations are a good choice for many applications. The primary reason users may want to use their own configurations is to support more complex eviction setups. See Chapter 4, Cache Eviction for more on the kinds of things you can do with eviction.

JGroups configuration is a complex area that goes well beyond the scope of this document. Users interested in exploring the details are encouraged to visit the JGroups website at http://www.jgroups.org as well as the JGroups wiki page at jboss.com.

The jgroups-stacks.xml file found in the org.hibernate.cache.jbc.builder package in the hibernate-jbosscache.jar provides a good set of standard JGroups configurations; these should be suitable for most needs. If you need to create your own configuration set, we recommend that you start with this file as a base.

The JGroups transport refers to the mechanism JGroups uses for sending messages to the group members. Choosing which transport to use is the main JGroups-related decision users will need to make. There are three transport types:

By default the Second Level Cache will use JGroups configurations found in the jgroups-stacks.xml file included in hibernate-jbosscache2.jar. Following are their names and a brief description of each:

udp

UDP multicast-based config; appropriate for all cache types. Includes JGroups flow control (FC) which is needed for caches that send significant numbers of asynchronous messages (i.e. timestamp caches and entity/collection caches configured for replication instead of invalidation). If you're not sure and want to use UDP multicast, this is the best choice.

udp-sync

UDP multicast-based config that omits JGroups flow control (FC). Optimal for caches that send little or no asynchronous messages, i.e. entity/collection caches configured for invalidation. Unsuitable for timestamp caches or entity/collection caches configured for replication.

tcp

TCP-based config with UDP multicast discovery (MPING). Includes JGroups flow control (FC); see udp above for the significance of that.

tcp-sync

TCP-based config with UDP multicast discovery (MPING). Omits JGroups flow control (FC); see udp-sync above for the significance of that.

tunnel

Uses a specialized protocol designed for cases where cluster members need to communicate across firewalls. See the JGroups documentation for details.

Chapter 4. Cache Eviction

4.1. Overview
4.1.1. The Eviction Process
4.1.2. Eviction Regions
4.1.3. Eviction Policies
4.2. Organization of Data in the Cache
4.2.1. Region Prefix and Region Name
4.2.2. Entities
4.2.3. Collections
4.2.4. Queries
4.2.5. Timestamps
4.3. Example Configuration
4.4. Best Practices

Eviction refers to the process by which old, relatively unused, or excessively voluminous data can be dropped from the cache, allowing the cache to remain within a memory budget. Generally, applications that use the Second Level Cache should configure eviction, unless only a relatively small amount of reference data is cached. This chapter provides a brief overview of how JBoss Cache eviction works, and then explains how to configure eviction to effectively manage the data stored in a Hibernate Second Level Cache. A basic understanding of JBoss Cache eviction and of concepts like FQNs is assumed; see the JBoss Cache User Guide for more information.

The JBoss Cache eviction process is fairly straightforward. Whenever a node in a cache is read or written to, added or removed, the cache finds the eviction region (see below) that contains the node and passes an eviction event object to the eviction policy (see below) associated with the region. The eviction policy uses the stream of events it receives to track activity in the region. Periodically, a background thread runs and contacts each region's eviction policy. The policy uses its knowledge of the activity in the region, along with any configuration it was provided at startup, to determine which if any cache nodes should be evicted from memory. It then tells the cache to evict those nodes. Evicting a node means dropping it from the cache's in-memory state. The eviction only occurs on that cache instance; there is no cluster-wide eviction.

An important point to understand is that eviction proceeds independently on each peer in the cluster, with what gets evicted depending on the activity on that peer. There is no "global eviction" where JBoss Cache removes a piece of data in every peer in the cluster in order to keep memory usage inside a budget. The Hibernate/JBC integration layer may remove some data globally, but that isn't done for the kind of memory management reasons we're discussing in this chapter.

An effect of this is that even if a cache is configured for replication, if eviction is enabled the contents of a cache will be different between peers in the cluster; some may have evicted some data, while others will have evicted different data. What gets evicted is driven by what data is accessed by users on each peer.

Controlling when data is evicted from the cache is a matter of setting up appropriate eviction regions and configuring appropriate eviction policies for each region.

JBoss Cache stores its data in a set of nodes organized in a tree structure. An eviction region is a just a portion of the tree to which an eviction policy has been assigned. The name of the region is the FQN of the topmost node in that portion of the tree. An eviction configuration always needs to include a special region named _default_; this region is rooted in the root node of the tree and includes all nodes not covered by other regions.

It's possible to define regions that overlap. In other words, one region can be defined for /a/b/c, and another defined for /a/b/c/d (which is just the d subtree of the /a/b/c sub-tree). The algorithm that assigns eviction events to eviction regions handles scenarios like this consistently by always choosing the first region it encounters. So, if the algorithm needed to decide how to handle an event affecting /a/b/c/d/e, it would start from there and work its way up the tree until it hits the first defined region - in this case /a/b/c/d.

An Eviction Policy is a class that knows how to handle eviction events to track the activity in its region. It may have a specialized set of configuration properties that give it rules for when a particular node in the region should be evicted. It can then use that configuration and its knowledge of activity in the region to to determine what nodes to evict.

JBoss Cache ships with a number of eviction policies. See the JBoss Cache User Guide for a discussion of all of them. Here we are going to focus on just two.

The org.jboss.cache.eviction.LRUPolicy evicts nodes that have been Least Recently Used. It has the following configuration parameters:

The org.jboss.cache.eviction.NullEvictionPolicy is a simple policy that very efficiently does ... nothing. It is used to efficiently short-circuit eviction handling for regions where you don't want objects to be evicted (e.g. the timestamps cache, which should never have data evicted). Since the NullEvictionPolicy doesn't actually evict anything, it doesn't take any configuration parameters.

In order to understand how to configure eviction, you need to understand how Hibernate organizes data in the cache.

All FQNs in a second level cache include two elements:

The FQN for the cache region where entities of a particular class are stored is derived as follows:

/ + Region Prefix + / + Region Name + /ENTITY

If no region prefix was specified, the leading / and Region Prefix is not included in the FQN. So, if hibernate.cache.region_prefix was set to "appA" and a class was mapped like this: 

<class name="org.example.Foo">
    <cache usage="transactional" region="foo_region"/>
    ....
</class>

The FQN of the region where Foo entities would be cached is /appA/foo_region/ENTITY.

If the class mapping does not include a region attribute, the region name is based on the name of the entity class, e.g. 

<class name="org.example.Bar">
    <cache usage="transactional"/>
    ....
</class>

the FQN of the region where Bar entities would be cached is /appA/org/example/Bar/ENTITY.

The FQN for the cache region where entities of a particular class is stored is derived as follows:

/ + Region Prefix + / + Region Name + /COLL

So, let's say our example Foo entity included a collection field bars that we wanted to cache: 

<class name="org.example.Foo">
    <cache usage="transactional"/>
    ....
    <set name="bars">
        <cache usage="transactional" region="foo_region"/>
        <key column="FOO_ID"/>
        <one-to-many class="org.example.Bar"/>
    </set>
</class>

The FQN of the region where the collection would be cached would be /appA/foo_region/COLL.

If the collection's <cache> element did not include a region, the FQN would be /appA/org/example/Foo/COLL.

Queries follow this pattern:

/ + Region Prefix + / + Region Name + /QUERY

Say we had the following query (again with a region prefix set to "appA"): 

List blogs = sess.createQuery("from Blog blog " + 
                              "where blog.blogger = :blogger")
    .setEntity("blogger", blogger)
    .setMaxResults(15)
    .setCacheable(true)
    .setCacheRegion("frontpages")
    .list();

The FQN of the region where this query's results would be cached would be /appA/frontpages/QUERY.

If the call to setCacheRegion("frontpages") were ommitted, the Region Name portion of the FQN would be based on a Hibernate class: /appA/org/hibernate/cache/StandardQueryCache/QUERY

Timestamps follow this pattern:

/TS/ + Region Prefix + /org/hibernate/cache/UpdateTimestampsCache

again with a / and the Region Prefix portion omitted if no region prefix was set.

Note that in the timestamps case the special constant ("TS") comes at the start of the FQN rather than the end. This makes it easier to ensure that eviction is never enabled for the timestamps region.

So far we've been looking at things in the abstract; let's see an example of how this comes together. In this example, imagine we have a Hibernate application with the following characteristics.

Let's see a possible eviction configuration for this scenario: 

<attribute name="EvictionPolicyConfig">
  <config>
         
    <attribute name="wakeUpIntervalSeconds">5</attribute>
    <attribute name="policyClass">org.jboss.cache.eviction.LRUPolicy</attribute>
          
    <!--  
      Default region to pick up anything we miss in the more
      specific regions below.
    -->
    <region name="/_default_">
       <attribute name="maxNodes">500</attribute>
       <attribute name="timeToLiveSeconds">300</attribute>
       <attribute name="minTimeToLiveSeconds">120</attribute>
    </region>
            
    <!--  Don't ever evict modification timestamps -->
    <region name="/TS" 
       policyClass="org.jboss.cache.eviction.NullEvictionPolicy"/>
            
    <!-- Reference data -->
    <region name="/appA/reference">
       <!-- Keep all reference data if it's being used -->
       <attribute name="maxNodes">0</attribute>
       <!-- Keep it around a long time (4 hours) -->
       <attribute name="timeToLiveSeconds">14400</attribute>
       <attribute name="minTimeToLiveSeconds">120</attribute>
    </region>
            
    <!-- Be more aggressive about queries on reference data -->
    <region name="/appA/reference/QUERY">
       <attribute name="maxNodes">200</attribute>
       <attribute name="timeToLiveSeconds">1000</attribute>
       <attribute name="minTimeToLiveSeconds">120</attribute>
    </region>
            
    <!-- 
       Lots of entity instances from this package, but different
       users are unlikely to share them. So, we can cache
       a lot, but evict unused ones pretty quickly.
    -->
    <region name="/appA/org/example/hibernate">
       <attribute name="maxNodes">50000</attribute>
       <attribute name="timeToLiveSeconds">1200</attribute>
       <attribute name="minTimeToLiveSeconds">120</attribute>
    </region>
            
    <!-- Clean up misc queries very promptly -->
    <region name="/appA/org/hibernate/cache/StandardQueryCache">
       <attribute name="maxNodes">200</attribute>
       <attribute name="timeToLiveSeconds">240</attribute>
       <attribute name="minTimeToLiveSeconds">120</attribute>
    </region>
            
  </config>
</attribute>

Notes on the above:

Some best practices to follow:

Chapter 5. Architecture

5.1. Hibernate Interface to the Caching Subsystem
5.2. Single JBoss Cache Instance Architecture
5.3. Multiple JBoss Cache Instance Architecture

We've now gone through all the main concepts and the configuration details; now we'll look a bit under the covers to understand a bit more about the architectural design of the Hibernate/JBoss Cache integration. Readers can skip this chapter if they aren't interested in a look under the covers.

The rest of Hibernate interacts with the Second Level Cache subsystem via the org.hibernate.cache.RegionFactory interface. What implementation of the interface is used is determined by the value of the hibernate.cache.region.factory_class configuration property. The interface itself is straightforward: 

void start(Settings settings, Properties properties) 
       throws CacheException;

void stop();

boolean isMinimalPutsEnabledByDefault();

long nextTimestamp();

EntityRegion buildEntityRegion(String regionName, 
                               Properties properties, 
                               CacheDataDescription metadata) 
            throws CacheException;

CollectionRegion buildCollectionRegion(String regionName, 
                                       Properties properties, 
                                       CacheDataDescription cdd) 
            throws CacheException;

QueryResultsRegion buildQueryResultsRegion(String regionName, 
                                           Properties properties) 
            throws CacheException;

TimestampsRegion buildTimestampsRegion(String regionName, 
                                       Properties properties) 
            throws CacheException;

Next, we'll look at the architecture of how the JBoss Cache integration implements these interfaces, first in the case where a single JBoss Cache instance is used, next in the case where multiple instances are desired.

The following diagram illustrates the key elements involved when a single JBoss Cache instance is used:

The situation when multiple JBoss Cache instances are used is very similar to the single cache case:

Copyright © 2009 Red Hat, Inc.