An examination of caching, Ehcache, Hibernate second level-cache, Terracotta caching, and the future.

1. Cold Hard Cache
Alex Miller (@puredanger)

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

3. Why cache?
• Temporal locality
• Non-uniform distribution

4. Temporal locality
Items:

5. Temporal locality
Cache:
Items:

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

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

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

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

10. 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

11. 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

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

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

14. Database offload
Operations
Per Second
Amount of Data

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

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

17. Ehcache

18. 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

19. Ehcache Architecture

20. 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

21. Ehcache 1.6 performance

22. Ehcache Performance vs memcached

23. Hibernate Second-Level Cache

24. 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

25. 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

26. 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

27. Terracotta as cache

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

29. 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”);

30. 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

31. 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

32. 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>

33. 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

34. New Hibernate cache visibility

35. 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

36. The future of caching...

37. 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

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

39. 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

40. 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)

41. 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