NoSQL mix
for a content repository
at scale

Thierry Delprat
tdelprat@nuxeo.com

https://github.com/tiry/

Some Context

Understanding the challenges & use cases

Document Repository

Storing objects (think {JSON} object)

  • Schemas
     
  • Streams
     
  • Security
     
  • Search
     
  • Audit

 

Custom Domain Model

Conversions & Previews

Security Policies

on any field

At SCALE

Application Log

REPOSITORY & Storage Adapters

REPOSITORY & Storage Adapters

Choose storage backends according to challenges

Store Structures
in SQL Database

or store Structures
in MongoDB

store streams
in MongoDB too

store streams
in S3

Leverage
Google Drive & Google Doc integration

Challenges

Search


 

Storage / Import


 

Async processing

SCaling SEARCH

the first challenge

Search everywhere

  • Simple search

     
  • Faceted search

     
  • Listings and views

     
  • Suggestion widgets

Challenges

  • Dynamic Queries
    • depends on Application Model
    • depends on User
       
  • Un-selective queries
     
  • Performance Challenges
    • Large number of documents
    • Can not always rely on DBA optimization work
    • Poor SQL DB infrastructure

Challenges

  • Dynamic Queries
    • depends on Application Model
    • depends on User
       
  • Un-selective queries
     
  • Performance Challenges
    • Large number of documents
    • Can not do DBA optimization work
    • poor SQL DB

Offload search queries to

Elasticsearch & Repository

One query
Several possible backends

Elasticsearch challenges

  • Asynchronous API
     
  • Non-transactional API
     
  • Need to recursively index security

Asynchronous batched updates
Ensure we can not lose any update

Async Indexing Flow

Mitigate Consistency Issues

  • Async Indexing  : 
    • Collect and de-duplicate Repository Events during Transaction
    • Wait for commit to be done at the repository level
      • then call elasticsearch
         
  • Sync indexing ( see changes in listings in "real time") :
    • use pseudo-real time indexing
      • ​​indexing actions triggered by UI threads are flagged
      • ​run as afterCompletion  listener
      • refresh elasticsearch index 

Pseudo-Sync Indexing Flow

ElasticSearch & Nuxeo

  • Offload queries from DB
    • Decouple sizing of search & storage
       
  • Good performances & Scalability
    • Always faster on complex queries
       
  • Great search features 
    • Fulltext
    • Aggregates
    • Fuzzy search

Scaling Storage

Big document databases and big imports

Giant DataSet

Challenges

Massive Imports

?

Mongo Document Database

No Impedance issue

less backend calls

no invalidation cost
 

Document level locking

no table level concurrency
 

Native distributed architecture

Easy scale out of read

MongoDB Challenges

Document level transactions
 

No MVCC isolation

Provide  shared mitigation policies

for critical use cases

Different transaction paradigm

Ensuring consistency

Transient State Manager

Run all operations in Memory

Populate an Undo Log

  • Recover Application level Transaction Management
    • Commit / Rollback model
       
  • "Read uncommited" isolation
    • Need to flush transient state for queries
    • "uncommited" changes are visible to others

Is Nuxeo Fast
with mongodb ?

SPEED

Significant RAW Speed improvements for most use cases

More importantly: some use cases are simply better handled

https://benchmarks.nuxeo.com/

More than RAW Performances

Side effects of no-cache

No Cache

Less memory per Connection 

More connections

More Concurrent Users

More than RAW Performances

Processing on large Document sets are an issue on SQL

Side effects of impedance miss match

Sample Nuxeo batch on 100,000 documents​

750 documents/s with SQL backend (cold cache)
 

11,500 documents/s with MongoDB / wiredTiger:  x15

lazy loading

cache trashing

MORE THAN RAW PERFORMANCES

Read & Write Operations
are competing

Write Operations
are not blocked

C4.xlarge (nuxeo)
C4.2Xlarge (DB)

SQL

READ + WRITE

Supersize-ME

Side effects of hyper-scaling the repository

Giant Repository

Millions of documents

  • Millions of events
    • Millions of Jobs

Indexing Jobs

Conversion Jobs

Audit update

Challenges

  • Distribute jobs across nodes
     
  • Have dedicated nodes
     
  • Make it scale for millions of Jobs 

Use shared Queues to manage Jobs

Already used for

Cache & Invalidations

Good match for Complex structures + Atomic API + Speed

Redis WorkManager

Giant ReDIS

  • Billions of documents
    • Billions of events
      • Billions of Jobs
        • ​Billions of Redis entries
          • ​Memory issues !  

Redis WorkManager

Kafka + Redis

KAFKA + REDIS

  • Queue Messages/Actions instead of Jobs
     
  • Minimize redis persistence
     
  • Optimize processing
    • pre-process messages (Audit)
    • regroup/batch some updates  

Benchmarking this

Results and lessons learned

1B benchmark

Key Figures

Initial import

  • Injection:  32,680 docs/s with peak at 40,400 docs/s.​
  • Indexing: 18,660 docs/s with peak at 27,400 docs/s​

https://benchmarks.nuxeo.com/

lessons Learned - MongoDB & ShArding

  • Sharding to leverage multiple nodes
    • more nodes = more disks = more IO (at least on AWS)
    • mongod + WiredTiger limits write concurrency to 128 (write tickets)
       
  • Indexing IO cost increases with volume
    • mitigate by increasing the number of nodes 
      • 4 nodes => slowdown at 600M / 6 nodes => slowdown at 900M
         
  • Sharding & Queries
    • requires query caching - don't mix queries & writes
  • Disable chunk balancing when using hash shard key
    •  avoid erratic re-organization

Lessons Learned

  • UUIDs vs Big Int
    • Smaller memory footprint and compact index
    • Faster to generate
       
  • Handling batch is not optional
    • Sequence generation by batch
    • Audit bulk write
       
  • Added stateful scroll api for the repository
    • needed for indexing more than 100M docs !
       
  • Elasticsearch performances
    • ​ES 2.x slower than 1.7 ( index.translog.durability)
    • Use a static mapping for speed

1B benchmark

3B benchmark

SOON

https://benchmarks.nuxeo.com/

Deployment

How to deploy that ?

DEPLOYMENT

Nuxeo Cluster

MongoDB Replicaset 

ES Cluster

Redis + Sentinel

Kafka Cluster

ZK Cluster

DEPLOYMENT

this is complex !

PaaS & Containers

PaaS & Containers

Makes it easier.

 

Leverage various storage sub-systems.

Any Questions ?

Thank You !

https://github.com/nuxeo

http://www.nuxeo.com/careers/

NoSQL

By Thierry Delprat

NoSQL

MongoDB + ElasticSearch + Redis + Kafka : NoSQL mix for a content repository at scale

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