When comparing MariaDB vs PostgreSQL, the Slant community recommends MariaDB for most people. In the question“What is the best database for backend web development?” MariaDB is ranked 1st while PostgreSQL is ranked 2nd. The most important reason people chose MariaDB is:
All development decisions for MariaDB can be reviewed and debated on a public mailing list or in the public bug tracker. Contributing to MariaDB is easy and the patch flow is fully transparent and public. But it's not all about the code contribution either - MariaDB also has very active documentation efforts and other related things that help developers in their day-to-day database administration.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Truly open development community
All development decisions for MariaDB can be reviewed and debated on a public mailing list or in the public bug tracker. Contributing to MariaDB is easy and the patch flow is fully transparent and public. But it's not all about the code contribution either - MariaDB also has very active documentation efforts and other related things that help developers in their day-to-day database administration.

Pro More cutting edge features
e.g. GIS since 5.3
Pro Dynamic column support
MariaDB has dynamic column support which allows for some NoSQL type functionality. So one database interface can provide both SQL and NoSQL for different software development needs.
Pro JSON datatype
JSON data can be stored as a column with optional indexes. It's like the best of the NO-SQL world without having to give up ACID and Relationships. This means that cascading deletes can be done in a single Transaction across multiple JSON documents.
Pro Advance access capabilities
Great security and inbuilt access management. Possible to configure row level access.
Pro Open source license
PostgreSQL is released under the PostgreSQL License, a liberal Open Source license, similar to the BSD or MIT licenses. A mirror of the source code can be found on GitHub
Pro High performance
PostgreSQL performance increases with each release, this is also proven by many benchmark tests.
Notable performance features include:
As PostgreSQL only supports one storage engine, it has been able to integrate and optimise it and with the rest of the database. This has resulted in multiple benefits such as the ability to allow different transaction types to co-exist efficiently without the need to select storage engine types once for each table ahead of time.
On the fly data compression resulting in less IO required for reading.
Asynchronous + synchronous Replication.
PostgreSQL supports a asynchronous API for use by client applications. It is reported to increase performance by up to 40% and is not supported by MySQL.
Designed to scale very well with large numbers of cores at high concurrency levels.
Cons
Con pgAdmin 4
The newest version of pgAdmin, written in Python and jQuery with Bootstrap, using the Flask framework, is not an improvement, it's bloated and not very intuitive. Some alternatives can be found here
Sadly also in the installers for older versions like PostgreSQL 9.6 the original pgAdmin was replaced by this version.
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