HSQLDB vs ObjectBox

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.

ObjectBox is an embedded, object-oriented NoSQL database for mobile applications and IoT devices. Its database provides native object APIs, relationships, reactive observers, ACID transactions and automatic schema migration. ObjectBox Sync can move data between devices and a backend or server, including for offline-first use cases. Listed language APIs include Java, Kotlin, Swift, Flutter/Dart, Go, Python and C/C++. The product supports vector search, with no embedding-column dimension limit stated in its FAQ. ObjectBox says it supports direct synchronization to MongoDB; connectors for other backend databases may require custom development. Its Sync Server can be self-hosted on POSIX systems and cloud providers, though ObjectBox does not currently provide cloud hosting. The core database plan is free; Sync pricing is quoted per project based on needs. The company describes its focus as mobile and IoT development, particularly decentralized systems with restricted devices and offline scenarios. Mesh Sync is available for Android Java/Kotlin and Flutter/Dart starting with version 6.0.0-beta, with APIs that may change before final release.