Ehcache 3: JSR-107 on steroids at Devoxx Morocco

@ljacomet#DevoxxMA #ehcache

Ehcache 3 JSR-107 on steroids

Louis Jacomet - Lead Software Engineer


Who am I? Louis Jacomet

Software engineer, closer to 40 than 20 and still coding!

@ Terracotta (Software AG) since 2013

Working on Ehcache mostly

Team manager and fiddling in infrastructure

No idea how to do a (nice) UI, especially a web one Enjoys concurrency, API design and hard problems


And what about you? Who knows nothing about caching? Who already uses caching in production? Who had production problems related to

caching?

Who knows about JCache?


AgendaCaching and JSR-107

Ehcache past and present

Ehcache 3 future


Caching and JSR-107


Caching Data structure holding a temporary copy of data Trade off between higher memory usage and

reduced latency

Targets Data which is reused Data which is expensive to compute / retrieve


Caches all over the place

CPU

Browser

Network

Disk


What should I cache? Keys

Proper equals/hashcode

Immutable Small(ish)

Value Proper equals/

hashcode

Ideally immutable Think concurrent

otherwise

Size matters


JSR-107 javax.cache

Java Community Process driven standard Specifies API and semantics for temporary,

in-memory caching of Java objects, including object creation, shared access, spooling, invalidation, and consistency across JVM's


JSR-107 Features CacheManager / Cache Expiration

Creation/Access/Update

Integration CacheLoader /

Writer

CacheEntryListener Created/Updated Removed/Expired Get old value

Entry processor Annotations MBeans, exposing

Configuration Statistics

No capacity control !


JSR-107 gotchas MutableConfiguration

Always invoke MutableConfiguration.setTypes(Class, Class)

Otherwise Cache only knows about Object Adding a CacheLoader factory is not enough -

need to invoke setReadThrough(boolean)


JSR-107 gotchas (2) Compare and Swap operations with a CacheLoader

Loader is ignored putIfAbsent checks Cache only, not underlying

system of record

Results in a weird contract


Ehcache past and present


A bit of history Announced in November 2003 on v1.0 released on September 2004

Only a few days before Java 5 and generics Acquired in 2009 by v2.0 released in March 2010 Terracotta acquired in 2011 by


Storage model: tiers Multiple storage tiers

Heap: like objects in a regular hash map Off-heap: binary form stored outside of

Garbage Collector reach

Disk: binary form stored on disk Clustered: binary form stored on other

server(s)


Overflow model

Heap

Disk


Heap

Disk

Overflow model


Disk

Heap

Overflow model


Authoritative tier model

Heap

Disk


Disk

Heap



Heap

Disk



Why the new model? Predictable latency

Every put pays the price of the lower / slowest tier

No degradation when a higher tier gets full Preserves fast(er) access for hot set

When a mapping is accessed it moves to the fastest tier available


Not a cache feature? Search

What does searching on a hot set means? Even without interacting with the cache, two

execution of the same query could return different results

Pinning Prevent eviction from cache entries May adversly effect the ability of the cache to

respect size constraints


Ehcache 3 The future is here


Lifecycle - explicit CacheManager

init / close methods create and close caches

PersistentCacheManager Maintenance mode Destroy cache data


Cache for proper typing Ehcache 2.x not generic, was time to change

that

Needs to be known at runtime No one wants a ClassCastException Cache data may live beyond application

lifecycle

Usage show that frequently key and values are of the same type in a given cache


Serialization Required as soon as we move away from the

heap

Fully customisable in Ehcache 3


CacheLoaderWriter Enables the cache-through pattern Consistent across all cache operations Single interface

Loader only - make sure write related methods throw

Writer only - what? Anyone having a good use case for this -

talk to us


Cache through - miss

Application Cache

Database


Cache through - hit

Application Cache

Database


Cache through - write

Application Cache

Database


Write behind Enables scaling your writes

Putter does not pay for write latency Batching and coalescing options Simplified compared to 2.x - no more sizing

gotchas


Application Cache

Database

queue

Write behind


Application Cache

Database

queue

Write behind - eviction

(K1, V1)

(K1, V1)


Application Cache

Database

queue

Write behind - eviction

(K1, V1)


Write behind - failure

Application Cache

queue

Database



Database


queue

Database



Expiry Offers context


Eviction Veto and Prioritizer Veto

Enables to suggest a veto on certain mappings Prioritizer

Allows to sort sample before picking eviction victim

Not applicable to all stores Both are hints only - capacity always takes priority


Transactions Full blown XA resource

includes recovery support Needs work for transaction managers

integration

Code isolated in its own module Currently part of the main Ehcache 3 jar


Clustering using Terracotta


Automatic Resource Control Enables sizing in natural units

n bytes on heap Percentage of the max heap available

Define resource pools at the cache manager Cross eviction amongst caches Enables auto balancing


Resilience strategy A cache is to be resilient Yet sh*t happens

Storage failures SLA violations (timeouts?)

Very explicit contract at this time To be refined when clustering is wrapping up


Q&AThank you for your time

Ehcache 3: JSR-107 on steroids at Devoxx Morocco

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Ehcache 3: JSR-107 on steroids at Devoxx Morocco

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