Cold Hard Cache
Alex Miller (@puredanger)

Agenda
• Why cache?
• Ehcache
• Hibernate 2nd level cache
• Terracotta
• The future....

Why cache?
• Temporal locality
• Non-uniform distribution

Temporal locality
Items:

Temporal locality
Cache:
Items:

Temporal locality
Hits: 0%
Cache:
Items:

Temporal locality
Hits: 0%
Cache:
Items:
Items:

Temporal locality
Hits: 0%
Cache:
Items:
Items:
Cache:

Temporal locality
Hits: 0%
Cache:
Items:
Items:
Cache:
Hits: 65%

Non-uniform distribution
Web page hits, ordered by rank
3200 100%
2400 75%
1600 50%
800 25%
0 0%
Page views, ordered by rank
Pageviews per rank
% of total hits per rank

Non-uniform distribution
Web page hits, ordered by rank
3200 100%
2400 75%
1600 50%
800 25%
0 0%
Page views, ordered by rank
Pageviews per rank
% of total hits per rank

Cache is always good right?
• Watch out for:
• Amdahl’s law
• Memory
• Concurrency
• Copy cost

Reduce latency
Page build Data retrieval
2000
1500
1000
500
0
No cache With cache

Database offload
Operations
Per Second
Amount of Data

DBs are sized to peak load
Operations
Per Second
Amount of Data

Strive to downsize DBs
Frequently accessed app data:
Shared Memory (Transactional)
Operations
Per Second
Business Record Data : Database
Amount of Data

Ehcache

Ehcache history
• First created in 2003 by Greg Luck
• Most widely used Java cache - 100k’s of deployments
• Apache 2.0 license
• JSR 107 Java cache implementation

Ehcache Architecture

Ehcache Features
• In-memory and spill-to-disk storage
• Cache bootstrap loaders
• Cache replication via listener API - RMI, JGroups, JMS
• Cache server with REST and SOAP APIs
• Servlet caching filter API
• Hibernate second-level cache support

Ehcache 1.6 performance

Ehcache Performance vs memcached

Hibernate Second-Level Cache

Hibernate Caching
Application Thread Application Thread
Session Session 1st Level Cache
Cache Cache Cache
Concurrency Concurrency Concurrency
Hibernate
Strategy Strategy Strategy
CacheProvider 2nd Level Cache
Cache Cache Cache
Region Region Region
Database

Entity and collection caches
• Entity and collection cache regions
• Mark a Hibernate entity or a collection in an entity as @Cacheable
• Specify a cache concurrency strategy
• ReadOnly, ReadWrite, NonstrictReadWrite, Transactional
• Turn on second level caching in the Hibernate config

Query Cache
• Query cache regions
• Mark HQL, Criteria, Query as cacheable
• Store result set id values
• Timestamp cache region - last update time for each entity type
• Useful for caching natural key lookups (non-primary key)
• ...but lots of hidden issues

Terracotta as cache

DistributedCache
• High-throughput clustered coherent cache
• Simple interface - basically ConcurrentMap
• Eviction options
• TTI, TTL
• Max in-memory size, max total size limits

DistributedCache Example
CacheConfig config = CacheConfigFactory.newConfig();
config.setMaxTTISeconds(30 * 60)
.setMaxTTLSeconds(2 * 60 * 60);
DistributedCache<String, Person> cache = config.newCache();
Person person = new Person(.......);
cache.put(“Alex”, person);
Person cached = cache.get(“Alex”);

DistributedCache features
• Built on high throughput ConcurrentDistributedMap
• Expiration based on either TTI or TTL
• Both in-memory and total target max limits
• Automatic memory management of caches
• Coherent clustered cache

Terracotta Hibernate Second Level Cache
• Easy integration and configuration
• Supports entity, collection, and query cache regions
• Supports read-only, read-write, and nonstrict-read-write cache
concurrency strategies
• Hibernate-specific tooling
• High performance with cache coherency

Enabling Second Level Cache
• Mark your entities with a cache concurrency strategy
• In hibernate.cfg.xml: <cache usage="read-write"/>
• With annotations: @Cache(usage=CacheConcurrencyStrategy.READ_WRITE)
• hibernate.cfg.xml
• <property name="cache.use_second_level_cache">true</property>
• <property name="cache.provider_class">
org.terracotta.hibernate.TerracottaHibernateCacheProvider</property>

Enabling Second Level Cache
• Define the tc-hibernate-cache.xml in your classpath
<?xml version=”1.0” encoding=”UTF-8”?>
<terracotta-hibernate-cache-configuration>
<default-configuration>
<time-to-idle-seconds>7200</time-to-idle-seconds>
<time-to-live-seconds>7200</time-to-live-seconds>
</default-configuration>
<cache>
<region-name>org.terracotta.authinator.domain.Account</region-name>
<!-- as many region-names here as you want -->
<configuration>
<time-to-idle-seconds>600</time-to-idle-seconds>
<time-to-live-seconds>600</time-to-live-seconds>
</configuration>
</cache>
</terracotta-hibernate-cache-configuration>
• Add the Terracotta Hibernate cache provider jar to your classpath
• -cp terracotta-hibernate-cache-1.0.0.jar
• Add the Terracotta Hibernate cache agent jar to your command line
• -javaagent:terracotta-hibernate-agent-1.0.0.jar

New Hibernate cache visibility

Performance - Read-Only Comparison
Throughput Latency
200K 100
Transactions per second
80
150K
Avg Latency (ms)
60
100K
40
50K
20
0K 0
Database IMDG EhcacheTerracotta Database IMDG EhcacheTerracotta

The future of caching...

Wonder twin powers, activate!
Terracotta Ehcache
• “Standard” cache apis (Ehcache / JSR 107)
• Low latency local cache
• High throughput clustered cache
• Coherent caching with options to degrade for greater performance
• Support for both “copy” and “shared object” caching

Single node and replicated Ehcache
• Same license, code base, and API
• Better visibility
• Better performance testing -> improved concurrency and performance
• Smooth migration path to...

Clustered Ehcache
• Short release for initial integration (probably Ehcache 1.7)
• Clustered store - partial API support
• Smooth upgrade from single node or replicated Ehcache
• New management and visibility features

Hibernate 2nd level cache
• More efficient in-memory and total count eviction (3.1.1)
• Better visibility of memory conditions
• Improved query caching
• Improved performance of core Terracotta (lock manager and memory
manager)

Thanks!
• Terracotta Open Source JVM clustering:
• http://www.terracotta.org
• Apress: “The Definitive Guide to Terracotta”
• by Ari Zilka, Alex Miller, Geert Bevin, Jonas
Boner, Orion Letizi, Taylor Gautier
• 2nd edition in progress....
• Alex Miller
• @puredanger
• http://tech.puredanger.com