n o sql d atabases : m ongo db vs c assandra. i ntroduction what is a database? “… a repository...
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INTRODUCTION What is a Database?
“… a repository with organized and structured data, … “ (Abramova & Bernardino, 2013-07)
Data can be accessed using DBMS (DataBase Management System)
What is DBMS? “ DBMS can be defined as a collection of
mechanisms that enables storage, edit and extraction of data” (Abramova & Bernardino, 2013-07)
SQL
SQL: Structured Query Language Became standard for:
Data interaction Data manipulation
Data Stored as set of tables
Accessing data from different tables at the same time is possible.
NOSQL
Carlo Strozzi presented NoSQL in 1980, back then, it refers to an open source database that didn’t use SQL interface.
Carlo Strozzi preferred to call it “noseequel” or “NoRel” Principle Difference
Popular after San Francisco conference held 2009
Why do we need NoSQL? In SQL ,efficiency in information extraction is affected
by the growth of data stored & used
CAP THEOREM
Based from CAP theorem, the following guarantees can be defined: Consistency Availability Partition tolerance
CAP theorem derives Relational and NoSQL principles
ACID
“ACID is a principle based on CAP theorem and used as set of rules for relational database transactions.“ (Abramova & Bernardino, 2013-07)
ACID guarantees: Atomic Consistent Isolated Durable
What if the amount of data is large? ACID may be hard to accomplish!
BASE PRINCIPLE & NOSQL
BASE principle: Basically Available Soft state Eventually consistent
BASE still follows CAP theorem. Two of the three guarantees should be selected if
the system is distributed.
TYPES OF NOSQL DATABASES
More than 150 different NoSQL databases Based on same principles Has some different characteristics.
Categories: Key-value Store Document Store Column-family Graph database
KEY-VALUE STORE
Data is stored as a group of key and value
All keys are unique
Data Access is done by relating those keys to values
Hash contains all keys in order to provide information when needed
DOCUMENT STORE
Databases are defined as set of Key-value stores that gets transformed into documents.
Each document is identified by unique key
Data access can be done using: key specific value
COLUMN FAMILY
Similar to relational database model Structure:
Column Super-Column Column family
Structure of database is defined by super-columns and column families.
Data access is accomplished by specifying column family, key and column in order to get value, using following structure:
<columnFamily>.<key>.<column> = <value>
GRAPH DATABASE
Those databases are used when data can be represented as graph, for example, social networks.
MONGODB
“MongoDB is an open source NoSQL database developed in C++” (Abramova & Bernardino, 2013-07).
MongoDB is a document store database Documents are gathered into groups according to
their structure
CAP theorem Consistency Partition tolerance
MONGODB (CONT.)
Description Data is sent to disc every 60 seconds. Everything is flushed to disc once new files are
created Each document is identified by “id” field An index for the “id” field is created
Characteristics Durability Concurrency
MONGODB CHARACTERISTICS
Durability Durability of data is accomplished by the
creation of replicas. Master-Slave technique
Master: read & write Slave: read Slave with recent data becomes Master if the Master
goes down Replicas are asynchronous
Concurrency Locks
CASSANDRA “Cassandra is a NoSQL database developed by Apache
Software Foundation; written in Java” (Abramova & Bernardino, 2013-07)
Similar to the usual relational model Difference is that stored data can be:
semi structured unstructured.
CAP theorem Partition tolerance High Availability
Designed to save large amount of data and deal with huge volumes in an efficient way.
CASSANDRA (CONT.)
Peer-to-peer architecture (NO MASTER) High availability High scalability
Replicates data over multiple nodes in a cluster.
Replication Factor: Total number of replicas. RF(1): 1 copy of each row on 1 node RF(2): 2 copies of same records on 2 nodes
Fail nodes are replaced with no downtime, and they are detected using “gossip” protocols
CASSANDRA (CONT.)
Replication Strategy: Simple: single data center Network Topology: multiple data centers
Cassandra Characteristics: Durability:
Two replication types: Synchronous Asynchronous
All writes & redundancies are known using a commit log.
Indexing: “Each node maintains the indexes of the table it
manages”
Data is manipulated using CQL
YCSB
“The YCSB – Yahoo! Cloud Serving Benchmark is one of the most used benchmarks to test NoSQL databases” (Abramova & Bernardino, 2013-07).
YCSB has a client that consists of two parts: Workload generator Set of workloads.
Workloads are combinations of: read Write update operations are done on randomly chosen records.
WORKLOAD A: 50%READS & 50% UPDATES
Abramova, V., & Bernardino, J. (2013-07). NoSQL Databases: MongoDB vs Cassandra. 19
WORKLOAD B: 95% READS & 5%UPDATES
Abramova, V., & Bernardino, J. (2013-07). NoSQL Databases: MongoDB vs Cassandra. 20
WORKLOAD C: 100% READS
Abramova, V., & Bernardino, J. (2013-07). NoSQL Databases: MongoDB vs Cassandra. 20
WORKLOAD F: READ-MODIFY-WRITE
Abramova, V., & Bernardino, J. (2013-07). NoSQL Databases: MongoDB vs Cassandra. 20
WORKLOAD G: 5% READS 95% UPDATES
Abramova, V., & Bernardino, J. (2013-07). NoSQL Databases: MongoDB vs Cassandra. 20
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