NoSQL Riak MongoDB Elasticsearch - All The Same?

MongoDB, Elasticsearch,
Riak – all the same?
Eberhard Wolff
Freelancer
Head Technology Advisory
Board adesso AG
http://ewolff.com

Eberhard Wolff - @ewolff
Leseprobe:
http://bit.ly/CD-Buch

Modeling:
Relational
Databases vs.
JSON

Financial System
•  Different financial products
•  Mapping objects / database
•  Inheritance

E/R Model
Asset
Stock
Zero
Bond
Option
Country> 20 database tables
Up to 25 attributes
Currency

JOINs
L

Get all asset
with interest
rate x

Asset
Type ID
Zero
Bond
Interest
Rate
Fixed
Rate
Bond
Interest
Rate
Stock Option
…
Preferred Underlying
asset
Country
Price
Country
Currency

{
"ID" : "42",
"type" : "Fixed Rate Bond",
"Country" : "DE",
"Currency" : "EUR",
"ISIN" : "DE0001141562",
"Interest Rate" : "2.5"
}

All stores in this
presentation
support JSON

Scaling
Relational
Databases

Larger Server
DB Server DB Server
Expensive
Server
Limited

Common Storage
DB Server
Expensive
Storage
Limited
DB Server
DB Server DB Server
e.g. Oracle
RAC

Replication
Cheap Server
Almost
unlimited
DB Server
DB Server DB Server DB Server
Inconsistent
data
Conflict resolution
or Read only

Replication
DB Server
DB Server DB Server DB Server
MySQL
Master-Slave
Oracle
Advanced
Replication

Network Failure
•  Either
Answer
& provide outdated data
•  or
Don’t answer
i.e. always provide up to date data

CAP
•  Consistency
•  Availability
•  Network Partition Tolerance
•  If network fails
provide a potentially incorrect answer
or no at all?

BASE
•  Basically Available
•  Soft State
•  Eventually (= in the end) consistent
•  i.e. give potentially incorrect answer

BASE and Relational DBs
•  Very limited
•  Stand by
•  Read only replica
•  No truly distributed DB

Relational & BASE
•  Most relational operations cover
multiple tables
•  Needs locks across multiple servers
•  Not realistically possible

NoSQL & BASE
•  Typical operation covers one data
structure
•  …that contains more information
•  No complex locking
•  More sophisticated BASE

Naïve View on
NoSQL

Key / Value Stores
•  Map Key to Value
•  For simple data structure
•  Retrieval only by key
•  Easy scalability
•  Only for simple
applications
Key Value
42 Some
data

Document Oriented
•  Documents
e.g. JSON
•  Complex
structures &
queries
•  Still great scalability
•  For more complex
applications
{
"author":{
"name":"Eberhard Wolff",
"email":"eberhard.wolff@gmail.com"
},
"title": "Continuous Delivery”,
}

Graph,
Column
Oriented…

Educated
View on
NoSQL

Key / value
Document-based
Search engine
All the same?

MongoDB
elasticsearch
Riak

•  Key / value
•  Truly distributed database
What is Riak?

Riak: Technologies
•  Erlang
•  Open Source (Apache 2.0)
•  Company: Basho

•  Allows secondary indices
•  Riak Search 2.0: Solr integration
•  Solr: Lucene based search engine
•  API compatible to Solr
•  Key / value or document based?
More indices

•  Map/reduce
•  Scans all datasets
•  Can store large binary objects
More Features

Scaling Riak
•  Based on the Dynamo paper
•  Well understood
•  …and battle proofed at Amazon

Scaling Riak
Server A
Shard1 Shard3
Shard4
Server B
Shard2 Shard1
Shard4
Server D
Shard4 Shard2
Shard3
Server C
Shard3 Shard2
Shard1

Scaling Riak
Server A
Shard1 Shard3
Shard4
Server B
Shard2 Shard1
Shard4
Server D
Shard4 Shard2
Shard3
Server C
Shard3 Shard2
Shard1
New Server

Tuning BASE
•  N node with replica
•  R nodes read from
•  W nodes written to
•  Trade off

Is it bullet
proof?

Jepsen
•  Test suite for network failures etc
•  https://aphyr.com/tags/jepsen
•  Riak succeeds
•  …if tuned correctly
•  …might still need to merge versions
•  https://aphyr.com/posts/285-call-me-
maybe-riak

•  Document-oriented
•  MMAPv1
Memory-mapped files + journal
•  New in 3.0: WiredTiger for complex
loads
Humongous
What is MongoDB?

MongoDB: Technologies
•  C++
•  Open Source (AGPL)
•  Company: MongoDB, Inc.

•  Can store large binary objects
•  Its own full text search
More Features

More Features
•  Map / Reduce
•  JavaScript
•  Aggregation framework

Scaling MongoDB
Replica 1
Shard 1
Replica 2
Replica 3
Shard 2
Replica 1
Replica 2
Replica 3

Availability
Replica 1
Shard 1
Replica 2
Replica 3
Shard 2
Replica 1
Replica 2
Replica 3

Scaling MongoDB
Replica 1
Shard 1
Replica 2
Replica 3
Replica 1
Shard 2
Replica 2
Replica 3
Replica 1
Shard 3
Replica 2
Replica 3

Scaling MongoDB
Replica 1
Shard 1
Replica 2
Replica 3
Shard 2
Replica 1
Replica 2
Replica 3
?

Tuning BASE
•  Write concerns
•  How many nodes should
acknowledge the write?
•  Read from primary
•  …or also secondaries

Jepsen
•  Mongo loses writes
•  A bug – might still be there
•  Also: non-acknowledge writes might
still survive
•  …and overwrite other data
maybe-mongodb

Database
=Storage
+ Search

elasticsearch
=Storage
+ Search

What is elasticsearch?
•  Search Engine
•  Also stores original documents
•  Based on Lucene Search Libray
•  Easy scaling

elasticsearch: Technologies
•  Java
•  REST
•  Open Source (Apache)
•  Backed by company elasticsearch

elasticsearch Internals
•  Append only file
•  Many benefits
•  But not too great for updates

Scaling elasticsearch
Server Server Server
Shard 1 Replica 1
Replica 2 Shard 2
Replica 3Shard 3

Tuning BASE
•  Write acknowledge: 1, majority, all
•  Including indexing
•  Read from primary
•  …or also secondaries

Jepsen
•  Loses data even if just one node is
partioned (June 2014)
•  Actively worked on
•  It’s a search engine…
maybe-elasticsearch
•  http://www.elasticsearch.org/guide/
en/elasticsearch/resiliency/current/

Scenarios
elasticsearch

Search
•  Powerful query language
•  Configurable index
•  Text analysis
•  Stop words
•  Stemming

Facets
•  Number of hits by category
•  Useful for statistics
•  & Big Data
•  Statistical facet (+ computation)
•  Range facets etc.

Conclusion
•  Relational databases might be
BASE
•  NoSQL embraces BASE better
•  Key / Value, Document stores and
search engine: very similar features
•  Care about scaling
•  Care about resilience

Thank You!

NoSQL Riak MongoDB Elasticsearch - All The Same?

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