Often times, huge web projects use multiple programming languages and even multiple databases. While relational database management systems (RDBMS) are common, they have limitations when it comes to the management of highly variable data. For such applications, NoSQL databases are a better alternative. The PostgreSQL RDBMS now provides Foreign Data Wrappers (FDW) that let PostgreSQL query non-relational external data sources.
FDWs are drivers that allow PostgreSQL database administrators to run queries and get data from external sources, including other SQL databases (Oracle, MySQL), NoSQL databases(MongoDB, Redis, CouchDB), text files in CSV and JSON formats, and content from Twitter. A few of the wrappers, such as the one for Kyoto Tycoon, allow PostgreSQL to handle both read and write operations on remote data.