A “PostgreSQL-compatible” database should work seamlessly with the applications and tools developed for PostgreSQL. This compatibility is achieved by implementing a similar set of features, functions, and syntax as the original PostgreSQL database.
Support for SQL (Structured Query Language) is a key feature that a PostgreSQL-compatible database must include. As the standard language for interacting with relational databases, it includes support for the same data types, operators, and functions used in PostgreSQL, plus a similar syntax for creating and manipulating tables, indexes, and views.
PostgreSQL Compatibility Levels
There are four levels of PostgreSQL compatibility. Compatibility is not an all or nothing sport. There can be degrees of compatibility since databases can lay anywhere along a level’s spectrum.
Claiming a database is compatible does not inherently mean it is 100 percent compatible and that existing applications will run without updates. Databases can only support applications to the degree that they can support that compatibility metric.
- Wire-Protocol Compatibility
A PostgreSQL database reads a set of commands and queries off the network. These commands and queries are written in a sequence of bytes and serialized. A “wire-protocol compatible” database can understand this same data sequencing and serialization. Wire-protocol compatibility allows PostgreSQL client drivers to communicate with the database. This means that developers experienced with PostgreSQL can easily build their applications. They can write the application using a variety of programming languages—Java, JDBC, Python, Go, etc—and can use command-line tools (psql, for example) to connect to the database and explore a large number of schemas or queries.
- Syntax Compatibility
Syntax compatibility relates to how a database parses the PostgreSQL syntax. In other words, if a valid PostgreSQL snippet is sent to the database, it should create a table, execute a SQL statement, and return a valid result. The way this is executed, however, might be different. For example, a specific set of parameters may be ignored. With proper syntax, developers can use some of PostgreSQL’s tools and frameworks. They send the necessary commands, and the database understands and follows them.
- Feature Compatibility
With feature compatibility, a database can support the advanced features in PostgreSQL— beyond the ANSI SQL standard—to help you get the most out of your data. Some of these advanced features include triggers, partial indexes, and stored procedures. On the other hand, an equivalent feature can have a different Postgres syntax to work. In this scenario, developers who rely on a specific Postgres feature would need to get up to speed with equivalent feature sets and make application modifications.
- Runtime Compatibility
Runtime compatibility is the highest level of PostgreSQL compatibility. It ensures that a database will match PostgreSQL execution semantics at runtime. More specifically, runtime-compatible databases should support queries to the system catalog, error messages, and error codes. Having runtime compatibility automatically implies that the other three compatibility metrics—wire, syntax, and feature—are in place. As a result, developers who know PostgreSQL will feel at home from start to finish.