# Database Transaction Models

## ACID Model

> *The ACID model provides a consistent system.*

* The ACID model ensures that a performed transaction is always consistent. This makes it a good fit for businesses that deal with online transaction processing (e.g., finance institutions) or online analytical processing (e.g., data warehousing). 

<table data-header-hidden><thead><tr><th width="142.33333333333331"></th><th></th></tr></thead><tbody><tr><td><strong>A</strong>tomicity</td><td><ul><li>"all or nothing"</li><li>If any part of the transaction fails entire transaction is aborted keeping the database unchanged.</li><li>each transaction is treated as a single unit, which succeeds completely or fails completely.</li></ul></td></tr><tr><td><strong>C</strong>onsistency</td><td><ul><li>enforces rules on data.</li><li>A processed transaction will never endanger the structural integrity of the database.</li><li>transactions can only take the data in the database from one valid state to another.</li></ul></td></tr><tr><td><strong>I</strong>solation</td><td><ul><li>Transactions cannot compromise the integrity of other transactions by interacting with them while they are still in progress.</li><li>concurrent transactions cannot interfere with one another and must result in a consistent database state.</li></ul></td></tr><tr><td><strong>D</strong>urability</td><td><ul><li>guarantees that once a transaction is committed, it will remain committed even in the state of power failure, or crash.</li><li>when a transaction has been committed, it will remain committed.</li></ul></td></tr></tbody></table>

#### Use Case Example&#x20;

* Financial institutions will almost exclusively use ACID databases. Money transfers depend on the atomic nature of ACID.
* An interrupted transaction that is not immediately removed from the database can cause a lot of issues. Money could be debited from one account and, due to an error, never credited to another.

## BASE Model

> *The BASE model provides high availability.*

<table data-header-hidden><thead><tr><th width="213"></th><th></th></tr></thead><tbody><tr><td><strong>B</strong>asically <strong>A</strong>vailable</td><td>BASE-modelled No-SQL databases ensure the availability of data by spreading and replicating it across the nodes of the database cluster.</td></tr><tr><td><strong>S</strong>oft State</td><td>Due to the lack of immediate consistency, data values may change over time.</td></tr><tr><td><strong>E</strong>ventually Consistent</td><td>The BASE model does not enforce immediate consistency. However, until it does, data reads are possible.</td></tr></tbody></table>

#### Use Case Example <a href="#ftoc-heading-6" id="ftoc-heading-6"></a>

* Marketing and customer service companies that deal with sentiment analysis will prefer the elasticity of BASE when conducting their social network research.&#x20;
* Social network feeds are not well structured but contain huge amounts of data that a BASE-modeled database can easily store.

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Which one to choose?

* Given their highly structured nature, ACID-compliant databases will be a better fit for those who require consistency, predictability, and reliability.
* Those who consider growth to be among their priorities will likely want to choose the BASE model because it enables easier scaling up and provides more flexibility.
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