APACHE SLING & FRIENDS TECH MEETUPBERLIN, 22-24 SEPTEMBER 2014

Oak, the Architecture of the new RepositoryMichael Dürig, Adobe Research

Design goals

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Scalable Big repositories Clustering Customisable, flexible OSGi friendly

Outline

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CRUD Changes Search

Tree model

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a d

b c

Updating

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?

x

a d

b c

MVCC

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a d

b c

r2: /dr1: /d

r1: /a/br2: /a/b

r1: / r2: /

r2: /d/x

HEAD

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Refresh and Garbage Collection

garbage

Refresh

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garbage

Garbage collection

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Concurrency and Conflicts

r2a

Concurrent updates

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r2br1

Merging

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r1 r3merge

r2b

r2a

upates

Conflict handling: serialisation

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Fully serialised Fail, no concurrent update

Partially serialised Concurrent conflict free updates

Conflict handling strategies: merging

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Partial merge Conflict markers, deferred resolution

Full merge Need to choose victim

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Replicas and Sharding

Replica and caches

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master copy full replica cache

Sharding strategies

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by path by level by hash with caching

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Implementations

MicroKernel / NodeStore

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Tree / Revision model implementation

Responsible for

Clustering

Sharding

Caching

Conflict handling

Not responsible for

Validation

Access control

Search

Versioning

Current implementations

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DocumentMK TarMK (SegmentMK)

Persistence MongoDB, JDBC Local FS

Conflict handling Partial serialisation Full serialisation

Clustering MongoDB clustering Simple failover

Sharding MongoDB sharding N/A

Node Performance Moderate High

Key use cases Large deployments (>1TB), concurrent writes

Small/medium deployments, mostly read

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Access Control

Accessible paths

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a d

cb

xistentialism

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All paths traversable Node may not exist Decorator on NodeStore

E

root.getChildNode("a").exists();

root.getChildNode("a") .getChildNode("b").exists();

⟹ false

⟹ true

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Comparing Revisions

Content diff

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What changed between trees Cornerstone for

Validation Indexing Observation …

What changed?

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∆

Example: merging

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r1

r2a

r2b

r3

r1 ➞ r2a“a” modified

“b” removed

∆

r1 ➞ r2b “d” modified

“x” added

∆

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Commit Hooks

Commit hooks

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Key plugin mechanism Higher level functionality

Validation (node type, access control, …) Trigger (auto create, defaults, …) Updates (index, …)

Editing a commit

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∆ ∆ + x

Commit hooks

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Based on content diff pass a commit fail a commit edit a commit

Applied in sequence

Type of hooks

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CommitHook Editor Validator

Content diff Optional Always Always

Can modify Yes Yes No

Programming model

Simple Callbacks Callbacks

Performance impact

High Medium Low

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Observers

Observers

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Observe changes After commit Often does a content diff Asynchronous Optionally synchronous

Local cluster node only

Examples

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JCR observation External index update Cache invalidation Logging

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Search

Query Engine

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SELECTWHERE x=y

/a//*

Parser

Parser

Parser

Index

Index

Traverse

Parser

Index

parse execute post process

Index Implementations

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Property (ordered) Reference Lucene

In-content or file system Solr

Embedded or external

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Big Picture

Big picture

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MicroKernel

Oak Core

Oak JCR

Oak API

NodeStore API

JCR API

Plugins

Resources

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http://jackrabbit.apache.org/oak/

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Appendix

Resources

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http://jackrabbit.apache.org/oak/

http://jackrabbit.apache.org/oak/docs/

https://svn.apache.org/repos/asf/jackrabbit/oak/trunk

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