Description: An external data wrapper allows access to data stored outside the database, facilitating the integration of information that does not reside in the main database management system (DBMS). This concept is especially relevant in environments where large volumes of data are managed across different sources, such as CSV files, file systems, or even other databases. The wrapper acts as an intermediary that translates standard SQL queries into operations that can interact with these external data, allowing users to perform queries and analysis without the need to import the data into the main database. This not only saves storage space but also improves efficiency by allowing real-time access to data that may change frequently. Additionally, external data wrappers are useful for creating unified views of data, where data from multiple sources can be combined in a single query, simplifying analysis and decision-making. In various database systems, extensions like PostgreSQL’s `postgres_fdw` or analogous tools are used to facilitate this functionality, allowing users to access data in other databases transparently.
History: The idea of wrapping external data in databases dates back to the early days of computing when the need to integrate different data sources became evident. However, the formal development of external data wrappers began to take shape in the 1990s with the rise of relational database management systems and the need to access distributed data. PostgreSQL, in particular, introduced the concept of ‘Foreign Data Wrappers’ (FDW) in its version 9.1, released in 2011, allowing users to access data in other databases more easily and efficiently.
Uses: External data wrappers are primarily used in environments where access to data not stored locally in the database is required. This includes integrating data from file systems, web services, and other databases. They are especially useful in data analysis applications, where combining information from multiple sources is needed to gain a more comprehensive view. They are also used in data migration, allowing organizations to access legacy data stored in old systems without the need for a complete migration.
Examples: A practical example of an external data wrapper is the use of `postgres_fdw` in PostgreSQL to access data stored in another PostgreSQL database. This allows users to execute SQL queries that combine data from both databases as if they were in a single one. Another case is accessing data in CSV files using the `file_fdw` extension, which allows users to query data stored in plain text files without the need to import it into the database.
