Dan Sullivan, PrincipalDS Applied Technologies

NoSQL Now! 2015August 18-20, 2015San Jose, California

ACID vs BASE:Yet Another False

Dichotomy

My Background◆ Data Architect / Engineer

◆ NoSQL and relational data modeler◆ Big data◆ Analytics, machine learning and text

mining◆ Cloud computing

◆ Author◆ No SQL for Mere Mortals◆ Contributor to TechTarget

◆ SearchDataManagement◆ SearchCloudComputing◆ SearchAWS

Overview◆ Quick Intro to ACID and BASE

◆ CAP Theorem

◆ Tradeoffs

◆ Finding a Sweet Spot on the Spectrum

◆ Questions

*Quick Intro to ACID and BASE

Image: blog.mark-taylor.com/Arizona/borrego/2014/08/08/what-is-your-bodys-ph-level/

*ACID

◆ Atomicity - All operations in a transaction succeed or fail together. No partial sets of operations.

◆ Consistency - The database is never in an inconsistent state.

◆ Isolation - Transactions do not interfere with one another

◆ Durability - Transactions are persistent over time and database restarts.

Image: http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/cr/m3/s3/

*BASE

◆ Basic Availability - Tolerate partial failure

◆ Soft State - state of database may change

◆ Eventual Consistency - may be inconsistent in short term, consistent in long term

Image: http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/cr/m3/s3/

*Just Say No To Food Fights

Image: www.zephoria.org/lakoff/2004/10/jon-stewart-on-crossfire.html

*CAP Theorem

Consistency Availability

Partition Tolerance

*You Can’t Have It All

*Actually, you can but … vertical scaling will cost you

*What are You Willing to Sacrifice?

Image: 9gagofthrones.com/tag/ned-stark-dead/

*Consistency? Which One?

◆ Causal

◆ Read-Your-Writes Consistency

◆ Session Consistency

◆ Monotonic Read Consistency

◆ Monotonic Write Consistency

Image: www.pitara.com

*Tradeoffs

*Write Consistency: How Low Can You Go?

◆ Consistency level of NoSQL DB specifies number of successful writes needed

◆ Lower consistency level can yield lower latency operations

◆ Higher consistency yields potentially higher availability

Image: www.bigtrends.com

*Read Consistency: Do You See What I

See?

◆ Network Partitions Fail

◆ Writes are not replicated immediately

◆ Possibly,same query different result

Image: www.pitara.com

*What is Your Tolerance?

Image: www.rosstraining.com (modified)

Inconsistency

*Finding a Sweet Spot on the ACID-

BASE Spectrum

*Partitioning

◆ Functional Partitioning◆ Decompose data by function◆ Use constraints to ensure integrity◆ Isolate constraints to a functional group◆ Vertically scale by functional group

◆ When Functional Partitioning is Not Enough Shard◆ Split functional groups of data across database servers◆ Benefits fo scalability and availability ◆ Introduces CAP Theorem Constraints

*Out of the Database and Into the Application

◆ Without ACID transactions in database, application handles more data management

◆ Balance low latency with high availability

◆ Application code becomes complex when need strong consistency and wide-area replication

Image: http://www.learnamericanenglishonline.com/

*Questions to Ask

◆ Can you tolerate inconsistency across functional groups?

◆ Which type of consistency is needed?

◆ Is short term inconsistency acceptable?

◆ Can an end user ever see the effect of an inconsistent state?

Image: http://www.learnamericanenglishonline.com/

*Where is this Leading?Image: http://www.learnamericanenglishonline.com/

“Google is living a few years in the future and sending the rest of us messages.”Doug Cutting

Hadoop Co-creator

◆ Increasing Support for ACID in NoSQL

◆ Fine-grained Management of CAP Constraints◆ Paxos state machines◆ Replication controlled at application level◆ Synchronous replication (Google Megastore), longer latency

◆ Point in time Consistency

◆ Better methods to deal with clock uncertainty

*From the Makers of BigTable

Image: http://static.googleusercontent.com/media/research.google.com/en//archive/spanner-osdi2012.pdf

Inconsistency

Questions?