Computer-implemented techniques described herein provide efficient data decoding using runtime specialization. In an embodiment, a method comprises a virtual machine executing a body of code of a dynamically typed language, wherein executing the body of code includes: querying a relational database, and in response to the query, receiving table metadata indicating data types of one or more columns of a first table in the relational database. In response to receiving the table metadata: for a first column of the one or more columns, generating decoding machine code to decode the first column based on the data type of the first column, and executing the decoding machine code to decode the first column of the one or more columns.