A ‘query’ is a single operation to request information from the database. A ‘transaction’ is a sequence of operations that can manipulate data in the database. The basic storage operations are commonly referred to as ‘CRUD’, which stands for: create, read, update, and delete. 

To optimize retrieval of information from the database, PostgreSQL makes use of indexes—copies of a portion of a table that are reorganized for faster search. Conceptually, these are similar to an index at the end of a book that allows you to find an item quickly without having to scan the entire book.

As a relational database, PostgreSQL uses formal descriptions called “schemas” to describe the structure of the contained data. In particular, a schema is the collection of tables, indexes, and functions in the database, and PostgreSQL supports multiple schemas. 

Database professionals are responsible for designing a schema and set of indexes that best represent the data and the way it’s used by application users. They are also in charge of maintenance and operation tasks to keep the data secure and the database operating smoothly.

Since its development at Berkeley, PostgreSQL has remained open source, meaning that the code is completely open for viewing, modification, and distribution. 

Developers can use open source databases for their applications with no licensing cost and with full flexibility in deployment, since these databases run on a wide variety of cloud and non-cloud platforms. A community of developers contribute to the improvement and maintenance of the software, improving security and reliability.

The popularity of PostgreSQL has risen in recent years, making it one of the most-used databases worldwide. It offers a number of benefits:

• Reliable and secure. PostgreSQL is highly fault-tolerant, maintaining data durability and maximizing uptime. It supports a strong authentication and authorization model, as well as several encryption methods—including end-to-end data encryption using SSL.
• High performing. PostgreSQL stores data in a structured way that allows it to efficiently insert, delete, and modify data. It’s also efficient for lookups and joins. Additionally, PostgreSQL can scale with multiple CPUs in parallel, speeding queries even further. 
• Compliant. Given their high compliance with the SQL standard, PostgreSQL databases are easy for both building apps and migrating existing ones. They are also ACID compliant, which means that your data is valid even amid hardware, software, or network disruptions.
• Highly extensible. PostgreSQL supports a wide range of data types (including advanced and user-created types), multiple coding languages, and the ability to write custom functions. It also has an extension mechanism for adding new functionality.
• Simple to monitor. PostgreSQL provides several statistics to support collection and reporting of server activity. Several external tools to monitor database activity and analyze performance are available.

Extensions enable you to expand and tailor the functionality of your database to your specific requirements. PostgreSQL offers comprehensive extension support, with extensions behaving just like built-in functions—including those developed externally.

Some commonly used extensions are:

• PostGIS. Supports storing, indexing, and querying geospatial data. Used for a variety of geospatial applications, including navigation.
• pgvector. Enables storing, indexing, and querying vectors and running vector similarity searches. Used for generative AI and natural language processing.
• pglogical. Replicates data robustly using logical replication. Used for replicating between PostgreSQL databases and supports granular table-level replication.

PostgreSQL supports both basic data types and advanced data types not commonly found in other databases, including boolean, number, integer, timestamp, array, and more. Developers can also create their own data types.

Its default procedural language is an extension of pgSQL (PL/pgSQL), with procedural language extensions of Tcl, Perl, and Python included in the standard distribution (written as PL/Tcl, PL/Perl, and PL/Python). These loadable procedural languages enable the coding language to be used to create functions and trigger procedures. 

Many more languages are supported through extensions, including Java, Ruby, C, C++, Delphi, and JavaScript.

PostgreSQL enables you to code in multiple languages without recompiling the database, a key benefit for developers.

Yes, PostgreSQL has been ACID compliant since 2001. 

ACID (atomicity, consistency, isolation, durability) is a set of properties that describe how transactional databases ensure the data is valid. ACID compliance guarantees data quality even in the case of a network outage or hardware failure, and enables reading and writing at the same time without data loss or corruption. These principles are critically important to applications in many industries, including finance and healthcare. 

Say, for example, a banking application is transferring a balance between two accounts within the database. If there’s an outage or failure in the middle of the transaction, an ACID-compliant database ensures that the money doesn’t simply disappear or is credited more than once—the account balances always remain valid.