// the find
Wisser/Jailer
Database Subsetting and Relational Data Browsing Tool.
Jailer is a Java desktop and command-line tool that extracts a small, referentially intact slice of a production database and writes it out as topologically sorted SQL, DbUnit, XML, JSON or YAML. It also includes a data browser for following foreign-key and user-defined relationships by hand, which suits developers building test data or debugging against real rows without copying the whole database.
- Rows are emitted in dependency order, so the generated SQL loads without constraint violations. Cycles in parent-child relationships are detected and broken by deferring nullable foreign keys.
- The subsetter is also exposed as a documented API and published to a Maven repository, so extraction can run in a pipeline instead of only from the GUI.
- Where a schema lacks declared foreign keys, relationships can be supplied as CSV association files. The 'subset by example' mode lets you collect rows in the browser and have Jailer infer the model from them.
- The SQL console relates result rows back to their source tables by analysing the statement, which lets it add filter conditions to arbitrary queries.
- The AI features added in 2026 (subsetting assistant, query assistant, SQL advisor) send requests to Anthropic or OpenAI-compatible endpoints. The README does not say what schema names, sample values or query text leave the machine. For a tool mostly used on production data, that needs a clear answer before anyone turns these on.
- The README says any JDBC database works in principle, but describes dialect-specific handling only for its list of supported systems and says those features are needed for best results. Anything else runs on the generic path.
- Without declared foreign keys, the association CSVs have to be written and maintained by hand. The datamodel folder shows how much of a model that can be, and it drifts whenever the schema changes.
- The build is Ant-only (build.xml, with no Maven or Gradle build for the application). The repo also carries generated Javadoc, a Windows executable and binary H2 demo databases, which makes diffs and reproducible builds harder. Support is a SourceForge forum plus a single personal address.