The default MEMORY type stores all data changes to the disk in the form of a SQL script.

The HSQLDB engine loads them only partially and synchronizes the data to the disk on transaction commits.

This renders very large updates impossible without splitting the work into smaller parts.

These tables can participate, for example, in queries with JOINs and simplify spreadsheet processing and read-write non-durable in-memory data storage.

Advanced features include user-defined SQL procedures and functions, schemas, datetime intervals, updatable views, arrays, lobs, full and lateral joins and set operations.

Version 2.0, released in 2010, is mostly new code, written to conform to Standard SQL and JDBC 4 Specification.