Datomic Spotlight - Speaker Deck

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DATOMIC @amitayh THE FUNCTIONAL DATABASE

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FULL DISCLOSURE ⚠

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ABOUT DATOMIC • Developed by Cognitect • Initial release 2012 • Designed by Rich Hickey (author of the Clojure programming language) • Used by Facebook, Netﬂix, more…

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FACTS ✅

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FACTS • “Abraham Lincoln is the president of the United States”

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FACTS • “Abraham Lincoln is the president of the United States” • “Abraham Lincoln was elected president of the United States on March 4, 1861”

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FACTS • Abraham Lincoln • Position • President • March 4, 1861 Entity Attribute Value Timestamp

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FACT = DATOM Entity Attribute Value Tx Operation

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FACT = DATOM Entity Attribute Value Tx Operation 1033 :first-name "Abraham" 260 add 1033 :last-name "Lincoln" 260 add 1033 :position "Lawyer" 277 add

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FACT = DATOM Entity Attribute Value Tx Operation 1033 :first-name "Abraham" 260 add 1033 :last-name "Lincoln" 260 add 1033 :position "Lawyer" 277 add 1033 :position "President" 522 add

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FACT = DATOM Entity Attribute Value Tx Operation 1033 :first-name "Abraham" 260 add 1033 :last-name "Lincoln" 260 add 1033 :position "Lawyer" 277 add 1033 :position "President" 522 add 1033 :position "President" 881 retract

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FACT BASED MODEL Facts Facts Facts Facts Facts Facts Facts Facts Time Facts Facts Time

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GIT Facts Facts Facts Facts Objects Facts Facts Objects Time Facts Objects Time

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A DATABASE • A collection of datoms • At a speciﬁc point in time • An immutable value

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DATABASE AS A VALUE • Same as 42 is a value • Safe to share, easy to reason about • Functions that take a database as an argument, or return a database

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TIME BUILT IN • Get the database value as of, or since, a point in time • See how the database would have looked like as if certain transactions took place • Reactive transaction reports

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QUERIES

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DATALOG • Equivalent to relational model + recursion • Declarative, expressive and powerful • Pattern matching style • No more string concatenation!

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EXAMPLE DATABASE Entity Attribute Value 42 :email [email protected] 43 :email [email protected] 42 :orders 107 42 :orders 141

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DATA PATTERN Constrains the results returned, binds variables: [?customer :email ?email] Attribute Value Entity

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DATA PATTERN Constrains the results returned, binds variables: [?customer :email ?email] Constant Variable Variable

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Entity Attribute Value 42 :email [email protected] 43 :email [email protected] 42 :orders 107 42 :orders 141 “Find all customers with emails” [?customer :email ?email]

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Entity Attribute Value 42 :email [email protected] 43 :email [email protected] 42 :orders 107 42 :orders 141 “Find a particular customer’s email” [42 :email ?email]

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Entity Attribute Value 42 :email [email protected] 43 :email [email protected] 42 :orders 107 42 :orders 141 “What attributes does 42 have?” [42 ?attribute]

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Entity Attribute Value 42 :email [email protected] 43 :email [email protected] 42 :orders 107 42 :orders 141 “What attributes and values does 42 have?” [42 ?attribute ?value]

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WHERE CLAUSE [:find ?customer  :where [?customer :email]] Data pattern

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FIND CLAUSE [:find ?customer  :where [?customer :email]]

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IMPLICIT JOIN [:find ?customer  :where [?customer :email] [?customer :orders]] “Find all the customers who have placed orders”

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PREDICATES [:find ?item  :where [?item :item/price ?price] [(< 50 ?price)]] “Find the expensive items”

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CALLING FUNCTIONS [:find ?customer ?product  :where [?customer :ship-address ?addr] [?adde :zip ?zip] [?product :product/weight ?weight] [?product :product/price ?price] [(Shipping/estimate ?zip ?weight) ?ship-cost] [(<= ?price ?ship-cost)]] “Find me the customer/product combinations where the shipping cost dominates the product cost”

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ARCHITECTURE

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DATABASE ROLES • Queries • Transactions • Consistency • Storage

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BREAK DOWN

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DATOMIC COMPONENTS Peer library Transactor Storage

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PEER LIBRARY Transactor Storage Peer library Your app • Embedded in your app • Executed queries locally

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Peer library Your app cache PEER LIBRARY Transactor Storage • Reads data from storage • Caches locally

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Peer library Your app cache Peer library Your app cache Peer library Your app cache SCALE HORIZONTALLY Transactor Storage

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TRANSACTOR Transactor Storage Peer library Your app • Standalone service • Scales vertically

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Transactor TRANSACTOR Transactor Storage Peer library Your app • Standalone service • Scales vertically • Hot standby for failover

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Transactor TRANSACTOR Storage Peer library Your app • Coordinates writes • Guarantees ACID transactions (isolation level “serializable”)

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Storage Transactor TRANSACTOR Peer library Your app • Writes transaction log to storage • Generates indices

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Peer library Your app cache Peer library Your app cache Peer library Your app cache Storage Transactor TRANSACTOR • Broadcasts live updates

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STORAGE Transactor Storage Peer library Your app • Provided as a service • Many different backends

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LOCAL STORAGE Transactor Storage Peer library Your app • Memory • Filesystem • Great for testing!

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NEARBY STORAGE Transactor Storage Peer library Your app • SQL database (any JDBC)

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DISTRIBUTED STORAGE ☁ Transactor Storage Peer library Your app • DynamoDB • Riak • CouchBase • Cassandra • …

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Peer library Your app cache Peer library Your app cache Peer library Your app cache SHARED MEMCACHED Transactor Storage Memcached

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EVENT SOURCING? • Datomic is lower level - facts vs events • Annotate transactions! • Querying already built in • Listen on transaction queue to build reactive systems

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Q&A

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RESOURCES • http://www.datomic.com/ • Intro to Datomic by Rich Hickey -  http://wix.to/b8CQABU • The Value of Values by Rich Hickey -  http://wix.to/D8CRABU • Datomic Datalog - http://wix.to/cMCQABU