ROBERT STUTTAFORD CTO, COGNICIAN Notes: http://is.gd/imm_db #rubyfuza Immutable data…base? 

Clojure 

Lisp Functional Immutable Dynamic Java & JS VMs OSS, 7 years old 

Lithp ... er, Lisp 

Functions are the unit of composition Created, stored, passed around for use by higher order functions, e.g. reduce. ! Prefer to use pure functions Those with no side-effects or I/O. Easier to reason about, test, and compose. Functional programming 

Define and call functions 

Immutable, persistent data structures Once defined, can’t change ‘under’ you. Changes create copies. Copies share structure internally. Far, FAR easier to reason about! 

This is what mutable state feels like, now! 

Clojure’s collections 

Prefer to pass unadorned data through mostly pure functions, ! rather than creating typed instances and mutating in place via methods. ! Then, both the data and the logic are easier to compose and test! TL;DR 

Datomic 

Datomic is a database of
flexible, time-based facts, supporting queries and joins,
with elastic scalability,
and ACID transactions. 

JVM, has REST API Closed source :-( Proprietary Paid licenses Free editions :-) Datomic 

Transactor
 Only 1 process Datomic’s architecture Consistent writes to storage Indexing Reads only while transacting 

Storage Datomic’s architecture Consistent writes to storage Indexing Reads only while transacting Abstracted, can use any of:
 Internal: In memory, on disk with transactor
 External: SQL, Riak, DynamoDB, and more Transactor
 Only 1 process 

Storage Peer Up to 30 procs Abstracted, can use any of:
 Internal: In memory, on disk with transactor
 External: SQL, Riak, DynamoDB, and more Reads from storage Inside your JVM app’s process Transparently cache from storage
 in local memory to satisfy reads Datomic’s architecture Consistent writes to storage Indexing Reads only while transacting Transactor
 Only 1 process 

Storage Query 1-64 peers Datomic’s architecture Memcached 2nd tier cache Peers look here before storage (paid licenses only) Paid licenses support high-availability transactor failover. Transactor
 Only 1 process 

Datomic’s data model [entity attr value] ! ! Entities have attributes with values. Each EAV combination is a ‘datom’. Entities typically have many datoms. 

Datomic’s data model [entity attr value] ! [123 :name “Robert”] [123 :likes “coffee”] 

Datomic’s data model [entity attr value tx] ! ! But what about time? 

Datomic’s data model [entity attr value tx] ! [123 :name “Robert” 456] [123 :likes “coffee” 456] [456 :tx-timestamp “2014-02-06”] Each datom refers to the transaction that created it. Transactions are also entities! 

Datomic’s data model [entity attr value tx] ! [123 :likes “coffee” 456] [456 :timestamp “2014-02-06”] [123 :likes “beer” 789] [789 :timestamp “2014-02-07”] 

Datomic’s data model Schema defines only how attribute’s values behave. ! Required: Name, data type, cardinality (one or many). Optional: indexed, unique, and more. ! Datomic does not proscribe how you combine attributes on entities! 

Let’s see some
code already! 

We are hiring! Pure Clojure, ClojureScript & Datomic Experience with other stacks OK! ! [email protected] @RobStuttaford 

Cape Town Clojure User Group Meet 1 or 2 Thursday evenings a month Next meet: 6-9pm,14 February 2014 Venue: Codebridge in Claremont @clj_ug_ct ! Talk notes: http://is.gd/imm_db