More for the database world

1. Intro to NoSQL databases
Redis & Mongo DB

2. Overview
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Redis
What, when, why, how
➲Mongo
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DB
What, when, why, how
Questions

3. Redis
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What is Redis
Redis is an open-source key-value data store
Primarily an in-memory database
Has the option of persisting data indefinitely
➲Key
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Data Structures
Strings, lists, sets, hashes, sorted sets

4. Why Redis
➲Speed
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– Redis is really fast
Hard to find specific numbers but I've seen claims
that it's up to 5-20 times faster than traditional
databases for certain applications
➲Specialized
– Has highly customized tools
that solves certain problems extremely
well.
➲This contrasts with a traditional RDBMS that
tries to be all things to all people
➲Generally seen as complimentary to a
traditional RDBMS

5. When To Use Redis
➲You
have to know the best type of data
structure and algorithm for solving the
problem you have
➲Redis publishes the Big-O notation
performance numbers for all it's operations
➲If redis supports that algorithm then you'll
probably want to use redis for it

6. Big O Review
➲O(1)
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– constant time.
Fastest any algorithm can be
Always takes the same amount of time
➲O(log(n))
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– logarithmic time
2nd fastest time
Uses a divide and conquer
➲O(n) – linear time
➲Others include
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O(n^2), O(c^n), O(n+m*log(m))

7. Using Redis
➲set x:y "{id:9000, email: 'test@axum.net'}"
➲get x:y
➲“set” - command
➲x:y – key
➲"{id:9000, email: 'test@axum.net'}" - value
➲By convention keys are of the form:
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z:y:x
➲But
other values are allowed

8. Using Redis
➲A
simple application is to use redis to count
page views
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incr stats:page:about
incrby ratings:video:1233 6

9. Mongo DB
➲MongoDB
has the same concept of a database that you are
familiar with
➲Within a MongoDB instance you can have zero or more
databases, each acting as high-level containers for
everything else.
➲A database can have zero or more collections. A collection
shares enough in common with a traditional table that you
can safely think of the two as the same thing.
➲Collections are made up of zero or more documents. Again,
a document can safely be thought of as a row.
➲

10. Mongo DB
➲A
document is made up of one or more fields, which you can
probably guess are a lot like columns.
➲Indexes in MongoDB function much like their RDBMS
counterparts.
➲Cursors - when you ask MongoDB for data, it returns a
cursor, which we can do things to, such as counting or
skipping ahead, without actually pulling down data.

11. Mongo DB
➲If
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Mongo is so similar to existing DBMS then why
use new terminology (collection vs. table,
document vs. row and field vs. column)?
relational databases define columns at the table level whereas a
document-oriented database defines its fields at the
document level.
Each document within a collection can have its own unique set of
fields.
A collection imposes less strict rules on a container in
comparison to a table
A document usually has a lot more information than a row.

12. Using Mongo
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The mongo CLI uses JavaScript syntax
db.help() prints the list of available commands
db.stats() prints the current information about your db
Since Collections do not have schemas we can do
the following:
db.unicorns.insert({name: ’Aurora’, gender: ’f’, weight: 450})
The 'unicorns collection will be created and document with name='Aurora' will be added to
it

13. Using Mongo
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Other Commands
db.unicorns.find() - returns list of documents in the 'unicorns' collection
"_id" : ObjectId("5239aaa9635c8909872a74fa"), "name" : "Aurora", "gender" :
"f", "weight" : 450 }
db.unicorns.find({gender: ’m’, weight: {$gt: 700}})
➲db.stats()
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prints the current information about your db
db.unicorns.update({name: ’Roodles’}, {weight: 590})

14. Demo
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15. Questions
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