NoSQL Tutorial: Types of NoSQL Databases & Example

Co je NoSQL?

NoSQL databáze is a non-relational data management system that does not require a fixed schema. It avoids joins, and is easy to scale. The major purpose of using a NoSQL database is for distributed data stores with humongous data storage needs. NoSQL is used for big data and real-time web apps. For example, companies like Twitter, Facebook, and Google shromažďují terabajty uživatelských dat každý den.

NoSQL databáze stands for “Not Only SQL” or “Not SQL”. Though a better term would be “NoREL”, NoSQL caught on. Carl Strozzi introduced the NoSQL concept in 1998.

Traditional RDBMS uses SQL syntax to store and retrieve data for further insights. Instead, a NoSQL database system encompasses a wide range of database technologies that can store structured, semi-structured, unstructured, and polymorphic data. Let us understand about NoSQL with a diagram in this NoSQL database tutorial:

Proč NoSQL?

Koncept NoSQL databází se stal populárním u internetových gigantů, jako je Google, Facebook, Amazonatd., kteří se zabývají obrovskými objemy dat. Při použití RDBMS pro velké objemy dat se doba odezvy systému zpomalí.

Abychom tento problém vyřešili, mohli bychom „rozšířit“ naše systémy upgradem našeho stávajícího hardwaru. Tento proces je drahý.

The alternative for this issue is to distribute the database load on multiple hosts whenever the load increases. This method is known as “scaling out”.

NoSQL database is non-relational, so it scales out better than relational databases, as they are designed with web applications in mind.

Stručná historie NoSQL databází

• 1998 – Carlo Strozzi uses the term NoSQL for his lightweight, open-source relational database.
• 2000 – Graph database Neo4j is launched.
• 2004 - Google BigTable is launched.
• 2005 - CouchDB je vypuštěn.
• 2007 – The research paper on Amazon Dynamo is released.
• 2008 – Facebook open sources the Cassandra projekt.
• 2009 – The term NoSQL was reintroduced.

Vlastnosti NoSQL

Nerelační

• NoSQL databáze nikdy nedodržují relační model.
• Never provide tables with flat fixed-column records.
• Work with self-contained aggregates or BLOBs.
• Do not require object-relational mapping and data normalization.
• No complex features like query languages, query planners, referential integrity joins, or ACID.

Bez schématu

• NoSQL databases are either schema-free or have relaxed schemas.
• Do not require any sort of definition of the schema of the data.
• Offer heterogeneous structures of data in the same domain.

Jednoduché API

• Offers easy-to-use interfaces for storage and querying data.
• APIs allow low-level data manipulation and selection methods.
• Text-based protocols mostly used with HTTP REST with JSON.
• Mostly used no standard-based NoSQL query language.
• Web-enabled databases running as internet-facing services.

Distribuováno

• Multiple NoSQL databases can be executed in a distributed fashion.
• Offers auto-scaling and fail-over capabilities.
• Often the ACID concept can be sacrificed for scalability and throughput.
• Mostly no synchronous replication between distributed nodes; asynchronous multi-master replication, peer-to-peer, HDFS replication.
• Only providing eventual consistency.
• Shared-nothing architecture. This enables less coordination and higher distribution.

Typy NoSQL databází

NoSQL databáze are mainly categorized into four types: Key-value pair, Column-oriented, Graph-based, and Document-oriented. Every category has its unique attributes and limitations. None of the above-specified databases is better at solving all the problems. Users should select the database based on their product needs.

Typy NoSQL databází:

• Na základě páru klíč–hodnota
• Sloupcově orientovaný graf
• Na základě grafů
• Orientace na dokumenty

Na základě páru klíčových hodnot

Data is stored in key/value pairs. It is designed in such a way to handle lots of data and heavy load. Key-value pair storage databases store data as a hash table where each key is unique, and the value can be a JSON, BLOB (Binary Large Objects), string, etc.

Například pár klíč-hodnota může obsahovat klíč jako „Webová stránka“ spojený s hodnotou jako „Guru99. "

It is one of the most basic NoSQL database examples. This kind of NoSQL database is used as a collection, dictionaries, associative arrays, etc. Key-value stores help the developer to store schema-less data. They work best for shopping obsah košíku.

Redis, Dynamo, and Riak are some NoSQL examples of key-value store databases. They are all based on AmazonPapír Dynamo.

Na základě sloupců

Column-oriented databases work on columns and are based on the BigTable paper by Google. Every column is treated separately. Values of single-column databases are stored contiguously.

They deliver high performance on aggregation queries like SUM, COUNT, AVG, MIN, etc., as the data is readily available in a column. Column-based NoSQL databases are widely used to manage data warehouses, business intelligence, CRM, and library card catalogs.

HBase, Cassandra, and Hypertable are NoSQL query examples of column-based databases.

Orientace na dokumenty

Document-Oriented NoSQL DB stores and retrieves data as a key-value pair, but the value part is stored as a document. The document is stored in JSON or XML formats. The value is understood by the DB and can be queried.

In this diagram on your left, you can see we have rows and columns, and on the right, we have a document database which has a similar structure to JSON. Now for the relational database, you have to know what columns you have, and so on. However, for a document database, you have a data store like a JSON object. You do not need to define it, which makes it flexible.

The document type is mostly used for CMS systems, blogging platforms, real-time analytics, and e-commerce applications. It should not be used for complex transactions which require multiple operations or queries against varying aggregate structures.

Amazon SimpleDB, CouchDB, MongoDB, Riak, and Lotus Notes are popular document-oriented DBMS systémy.

Na základě grafu

A graph type database stores entities as well as the relations amongst those entities. The entity is stored as a node with the relationship as edges. An edge gives a relationship between nodes. Every node and edge has a unique identifier.

Compared to a relational database where tables are loosely connected, a graph database is multi-relational in nature. Traversing relationships is fast, as they are already captured in the DB, and there is no need to calculate them. Graph base databases are mostly used for social networks, logistics, and spatial data.

Neo4J, nekonečný graf, OrientDB, and FlockDB are some popular graph-based databases.

Nástroje Query Mechanism pro NoSQL

The most common data retrieval mechanism is the REST-based retrieval of a value based on its key/ID with a GET resource.

Document store databases offer more difficult queries, as they understand the value in a key-value pair. For example, CouchDB allows defining views with MapReduce.

Co je teorém CAP?

CAP theorem is also called Brewer’s theorem. It states that it is impossible for a distributed data store to offer more than two out of three guarantees:

1. Konzistence
2. dostupnost
3. Tolerance oddílů

Konzistence: Data by měla zůstat konzistentní i po provedení operace. To znamená, že jakmile jsou data zapsána, jakýkoli budoucí požadavek na čtení by měl tato data obsahovat. Například po aktualizaci stavu objednávky by všichni klienti měli vidět stejná data.

Dostupnost: Databáze by měla být vždy dostupná a reagovat. Neměl by mít žádné prostoje.

Tolerance oddílů: Tolerance oddílů znamená, že systém by měl nadále fungovat, i když komunikace mezi servery není stabilní. Servery mohou být například rozděleny do několika skupin, které spolu nemusí komunikovat. Zde platí, že pokud je část databáze nedostupná, ostatní části nejsou vždy ovlivněny.

Případná konzistence

The term “eventual consistency” means to have copies of data on multiple machines to get high availability and scalability. Thus, changes made to any data item on one machine have to be propagated to other replicas.

Data replication may not be instantaneous, as some copies will be updated immediately while others in due course of time. These copies may be mutually inconsistent, but in due course of time, they become consistent. Hence, the name eventual consistency.

BÁZE: Basticky Ak dispozici, Sčasto stát, Eventivní konzistence

• Basically available means the DB is available all the time as per the CAP theorem.
• Soft state means even without an input, the system state may change.
• Eventual consistency means that the system will become consistent over time.

Výhody NoSQL

• Can be used as a primary or analytic data source.
• Big data capability.
• No single point of failure.
• Easy replication.
• No need for a separate caching layer.
• Poskytuje rychlý výkon a horizontální škálovatelnost.
• Can handle structured, semi-structured, and unstructured data with equal effect.
• Object-oriented programming which is easy to use and flexible.
• NoSQL databases do not need a dedicated high-performance server.
• Support key developer languages and platforms.
• Simpler to implement than using RDBMS.
• Může sloužit jako primární zdroj dat pro online aplikace.
• Handles big data which manages data velocity, variety, volume, and complexity.
• Excels at distributed database and multi-data center operations.
• Eliminates the need for a specific caching layer to store data.
• Offers a flexible schema design which can easily be altered without downtime or service disruption.

Nevýhody NoSQL

• No standardization rules.
• Limited query capabilities.
• RDBMS databases and tools are comparatively mature.
• Nenabízí žádné tradiční databázové funkce, jako je konzistence při provádění více transakcí současně.
• When the volume of data increases, it is difficult to maintain unique values as keys become difficult.
• Does not work as well with relational data.
• The learning curve is stiff for new developers.
• Open source options are not so popular for enterprises.

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