Post on 14-Aug-2015
Three things you need
to know about data modelingMatthew Revell
matthew@couchbase.com, @matthewrevell
Lead Developer Advocate, Couchbase
1
We’re still learning
Data modeling books
©2014 Couchbase, Inc. 3
Three query methods
Application layer computation Off-load computation
Predictable queries Key-value: pre-computed answers Views
Ad-hoc queries N1QL and key-value with manual
indexes
N1QL and views
©2014 Couchbase, Inc. 4
Key-value
Key-value
Pre-compute answers asynchronously
Store object state
Choose when to embed data and when to refer to it
Design your keys well
©2014 Couchbase, Inc. 6
Pre-computed answers
We’re used to asking questions
©2014 Couchbase, Inc. 8
Key-value look-ups give us a library of answers
©2014 Couchbase, Inc. 9
Answer-oriented databases
©2014 Couchbase, Inc. 10
http://martinfowler.com/bliki/AggregateOrientedDatabase.html
Airline bookings
©2014 Couchbase, Inc. 11
Embed or refer?
How much should we denormalize?
An e-commerce order
©2014 Couchbase, Inc. 13
The same order in a document
©2014 Couchbase, Inc. 14
Embedded vs. referred data
©2014 Couchbase, Inc. 15
You should embed data when:
Speed trumps all else
Slow moving data
No duplication
Application layer can keep multiple copies of same data in sync
When to embed data
©2014 Couchbase, Inc. 16
You should refer to data when:
Consistency is a priority
The data has large growth potential
When to refer to data
©2014 Couchbase, Inc. 17
Key design
Key design is as important as document design.
There are three broad types of keys:
Human readable/deterministic: e.g., an email address
Computer generated/random: e.g., a UUID
Compound: e.g., a UUID with a deterministic portion
Three ways to build a key
©2014 Couchbase, Inc. 19
Human readable/deterministic key
©2014 Couchbase, Inc. 20
public class user {
private String name;private String email;private String streetAddress;private String city;private String country;private String postCode;private String telephone;private Array orders;private Array productsViewed;
}
{"name": "Matthew Revell","address": "11-21 Paul Street","city": "London","postCode": "EC2A 4JU","telephone": "44-20-3837-9130","orders": [ 1, 9, 698, 32 ],“productsViewed”: [8, 33, 99, 100]
}
Key: matthew@couchbase.com
Random/computer-generated key
©2014 Couchbase, Inc. 21
{"name": "Matthew Revell","email": "matthew@couchbase.com","address": "11-21 Paul Street","city": "London","postCode": "EC2A 4JU","telephone": "44-20-3837-9130","orders": [ 1, 9, 698, 32 ],“productsViewed”: [8, 33, 99, 100]
}
Key: 1001
Using counters to generate keys
©2014 Couchbase, Inc. 22
Application
user_id = incr(“counter_key")
add(user_id, data)
Creating a new user
add(email_address, user_id)
Application
key = get("matthew@couchbase.com")
get(key)
Finding a user by email address
Multiple look-up documents
©2014 Couchbase, Inc. 23
u::count
1001
u::1001
{ "name": “Matthew Revell",
"facebook_id": 16172910,
"email": “matthew@couchbase.com”,
“password”: ab02d#Jf02K
"created_at": "5/1/2012 2:30am",
“facebook_access_token”: xox0v2dje20,
“twitter_access_token”: 20jffieieaaixixj }
fb::16172910
1001
nflx::2939202
1001
twtr::2920283830
1001
em::matthew@couchbase.com
1001
em::matthew@understated.co.uk
1001
uname::mrevell
1001
Compound keys
Compound keys are look-up documents with predictable names.
They continue the discussion of embedded versus referred data.
Compound keys: an example
u::1001
{
"name": "Matthew Revell",
"email": "matthew@couchbase.com",
"address": "11-21 Paul Street",
"city": "London",
"postCode": "EC2A 4JU",
"telephone": "44-20-3837-9130",
"orders": [ 1, 9, 698, 32 ],
“productsViewed”: [8, 33, 99, 100]
}
Compound keys: an example
u::1001
{
"name": "Matthew Revell",
"email": "matthew@couchbase.com",
"address": "11-21 Paul Street",
"city": "London",
"postCode": "EC2A 4JU",
"telephone": "44-20-3837-9130",
"orders": [ 1, 9, 698, 32 ]
}
u::1001::productsviewed
{"productsList": [
8, 33, 99, 100]
}
Compound keys: an example
u::1001
{
"name": "Matthew Revell",
"email": "matthew@couchbase.com",
"address": "11-21 Paul Street",
"city": "London",
"postCode": "EC2A 4JU",
"telephone": "44-20-3837-9130",
"orders": [ 1, 9, 698, 32 ]
}
u::1001::productsviewed
{"productsList": [
8, 33, 99, 100]
}
p::8
{
id": 1,"name": "T-shirt","description": "Red Couchbase shirt","quantityInStock": 99,"image": "tshirt.jpg”
}
Compound keys: an example
u::1001
{
"name": "Matthew Revell",
"email": "matthew@couchbase.com",
"address": "11-21 Paul Street",
"city": "London",
"postCode": "EC2A 4JU",
"telephone": "44-20-3837-9130",
"orders": [ 1, 9, 698, 32 ]
}
u::1001::productsviewed
{"productsList": [
8, 33, 99, 100]
}
p::8
{
id": 1,"name": "T-shirt","description": "Red Couchbase shirt","quantityInStock": 99
}
p::8::img
“http://someurl.com/tshirt.jpg”
N1QL and Views!
The world beyond key-value
We’re not in Kansas any more
©2014 Couchbase, Inc. 30
N1QL and views
N1QL Views
Ad-hoc querying Predictable queries
Nested JSON in and unnested JSON
out
Number crunching
Large growth clusters Multidimensional and
geospatial queries
©2014 Couchbase, Inc. 31
N1QL
Indexes
Schema types and document types
Keyspaces
©2014 Couchbase, Inc. 32
Indexes
©2014 Couchbase, Inc. 33
• You always need at least one index
• PRIMARY index gives you all of the keys in the bucket
• Secondary indexes enable ad-hoc querying at speed
Indexes
©2014 Couchbase, Inc. 34
Indexes
©2014 Couchbase, Inc. 35
NEW Global Secondary Indexes Views
N1QL query to create a new indexJavaScript map/reduce
Option to run dedicated indexing and
query nodes
Queries always run on database nodes
ForestDB-backed Couchstore-backed
Supports multidimensional and geospatial
queries
Maintaining the schema and working with keyspaces
©2014 Couchbase, Inc. 36
JOINs work on primary keys and secondary keys.
They JOIN across and within keyspaces (for now, that means buckets).
Airlines:
airline_24 ← Key (“primary key”)
{
"id": "24",
"type": "airline",
"name": "American Airlines",
"iata": "AA",
"icao": "AAL",
"callsign": "AMERICAN",
"country": "United States",
"active": "Y"
}
Routes:
route_5966 ← Key
{
"id": "5966",
"type": "route",
"airline": "AA",
"airlineid": "airline_24", ← This is the foreign key
"sourceairport": "MCO",
"destinationairport": "SEA",
"stops": "0",
"equipment": "737",
"schedule": [...
]
}
Offloading computation to N1QL
©2014 Couchbase, Inc. 37
N1QL allows you to choose which elements are returned at the top level.
This is incredibly useful because it reduces the need to write complex
parsing logic:
• Within the application
• In client-side, front-end frameworks (Angular/Backbone etc.)
SELECT a.name, s.flight, s.utc, r.sourceairport, r.destinationairport,
r.equipment FROM `travel-sample` r UNNEST r.schedule s JOIN `travel-
sample` a ON KEYS r.airlineid WHERE r.sourceairport='LHR' AND
r.destinationairport='LAX' AND s.day=2 ORDER BY a.name
Questions!
Thanks!
Matthew Revell
matthew@couchbase.com
@matthewrevell