eXtremeDB vs HSQLDB

eXtremeDB is an in-memory database system designed for embedded devices and applications. It can combine in-memory and persistent storage within one database system. Interfaces include native APIs, REST, SQL, ODBC, and JDBC, with language APIs for C/C++, Java, Python, C#, Go, and Rust. For time-series data, a sequence type provides columnar storage. Distributed options include High Availability, Cluster, and Active Replication Fabric for replication across IoT tiers. Network communications can use TLS/SSL with OpenSSL or wolfSSL. Technical specifications list maximum database sizes of 4 GB on 32-bit architectures and 18.4 exabytes on 64-bit architectures. eXtremeDB supports Android, iOS, Linux, macOS, and Windows, and can be self-hosted. Evaluation downloads are listed for Linux, macOS, and Windows; custom trial packages can be requested for other platforms. McObject offers annual engineering support contracts that include software updates and a 50 percent discount on major upgrades. Commercial licensing is paid, with pricing available on request, and a 60-day trial is listed.

HSQLDB is a Java-based relational database engine for embedded or server use, with both in-memory and disk-based tables. It supports SQL:2023 core features and many optional features, plus lock-based and MVCC transaction models; the engine is fully multithreaded. Listed capabilities include JSON constructor functions, CSV loading and unloading, temporal system-versioned tables, row-level access control, and log-based replica synchronization. It includes a command-line SQL tool and simple GUI query tools. The latest official release listed is version 2.7.4, compatible with JDK 8 and above, and packages include Java 11 module jars as well as Java 8 jars for HSQLDB and SQL Tool. HSQLDB is self-hosted, with high availability, read replicas, and JSON data support listed. Its default combined limit for CACHED tables is 8TB, extendable to 256TB with a connection property; each TEXT table is limited to 256GB, and memory tables depend on available memory. The software is free to use in commercial products when license terms are met; its licenses are based on the new BSD License. The HSQLDB plan is free. A Developer subscription is $100 a year; Premier Corporate is $2,500 a year at the base level. Support options include community channels and paid commercial support.