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Apache Jena TDB is persistent RDF storage for Jena applications. Choose between TDB1 and TDB2 deliberately: they use incompatible database formats and tools. For a single application, access the store through Jena APIs or command-line tools with transactions; for multiple applications or processes, put Fuseki in front of the store rather than opening the database directly from multiple JVMs.
What Apache Jena TDB is—and where Fuseki fits
TDB is Jena’s native persistent RDF store for a single machine. You can access it through Jena APIs or manage it with command-line scripts. Fuseki is the serving layer: it can use TDB for persistent storage and expose SPARQL query and update protocols over HTTP. That separation lets applications share a server endpoint without each process opening the database files directly. Apache Jena’s TDB overview
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How TDB1 and TDB2 differ
TDB1 and TDB2 are separate systems, not interchangeable versions of one on-disk format. Jena states, “TDB2 is not compatible with TDB1.” Use the tools and APIs that match the database you created; do not point TDB1 utilities at TDB2 files, or vice versa. Apache Jena TDB2 documentation
| Decision | TDB1 | TDB2 |
|---|---|---|
| Database format | Incompatible with TDB2. | Incompatible with TDB1. |
| Transaction design | Serializable transactions using write-ahead logging. Jena describes transaction sizes as a few tens of millions of triples; this is a qualitative documented limit, not a benchmark. | Serializable transactions using copy-on-write MVCC. Jena documents no transaction size limit; TDB2 use is transactional-only. |
| Tools and APIs | Use TDB1 tools and APIs. | Use TDB2 tools and APIs. |
| Sharing between processes | Direct dataset access is intended for one JVM at a time; use Fuseki for application access. | Administration guidance recommends Fuseki2 for access across processes or machines. |
| Migration | Its database files cannot be opened as TDB2. | Migration requires reloading RDF data and updating application code to use TDB2 APIs. |
These documented differences do not establish that one version is universally faster. Loader behavior depends on hardware and workload, and Jena recommends trying the available loaders for the situation at hand. TDB2 command-line tools
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How transactions protect TDB data
Jena describes its transactions as serializable, its highest isolation level. With one active writer and multiple readers, a reader whose transaction began before a write commits continues to see the earlier state; a transaction begun after the commit sees the committed changes. Nested transactions are not supported. Apache Jena TDB transactions
Jena recommends transaction-based access because transactions help reduce the risk of corruption after unexpected process termination or system crashes. This is not a replacement for backups or sound operational practices. TDB1 uses write-ahead logging; TDB2 uses copy-on-write MVCC structures. Transaction documentation
How to load RDF into TDB2 safely
- Validate the input first. Run
riot --validateagainst the RDF input so syntax and data problems are found before loading. See Jena RDF input documentation. - Use the TDB2 command family. For example, use
tdb2.tdbloaderfor TDB2. Do not confuse it withtdbloader2, which is a TDB1 tool. TDB2 command-line tools - Select loader mode for your failure tolerance and workload. Jena says all TDB2 loaders can update datasets, but only the basic and sequential loaders are fully transactional in the presence of crashes. Faster, lower-level modes can leave the database in a strange state if a load fails. There is no documented universal fastest choice: performance depends on the hardware and workload.
Jena says bulk uploads into a live Fuseki can involve hundreds of millions of triples; that is an illustrative capability statement, not a throughput or completion-time guarantee. TDB2 documentation
How to share a TDB-backed dataset
Do not make simultaneous direct access from multiple JVMs your sharing design. Jena warns that direct simultaneous access can cause corruption. Run Fuseki/Fuseki2 with the TDB-backed store and have clients use its SPARQL HTTP interface instead. The database lock also prevents multiple JVM processes from using the same database simultaneously. TDB2 administration
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What migrating from TDB1 to TDB2 involves
- Export or otherwise obtain the RDF data from the TDB1 store using the appropriate TDB1 tools.
- Create a separate TDB2 store and reload the RDF into it using TDB2 tools.
- Change application code to use TDB2 APIs, then validate the application against the new store before switching production use.
TDB2 does not open existing TDB1 files directly, so migration is a data reload rather than an in-place format upgrade. Jena’s migration documentation describes the reload-and-update-code path. TDB migration guidance
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Backups, compaction, and other operations
TDB2 administration documentation covers database layout, locking, backups, and compaction. It says compacted generations other than the active one are not used or touched by TDB2 and can be managed separately. Check procedures for the release you run before moving or deleting database files; do not infer that any file that appears inactive is safe to remove. TDB2 administration
Jena’s command-line toolset includes utilities for loading, querying, updating, statistics, dumping, backup, and—on TDB2—compaction. The scripts are included in the binary distribution. TDB command-line tools
Release and Java requirements
The Apache Jena releases page checked on October 4, 2026 listed Jena 6.2.0 and stated, “Jena6 requires Java 21, or a later version of Java.” Release numbers and runtime requirements can change, so check the page before installing. The apache-jena binary distribution includes the APIs, SPARQL engine, native TDB storage, and command-line tools; Jena libraries are also available through Maven. Apache Jena releases and downloads
Heap size and SSD questions
Jena’s FAQ includes questions about suitable Java heap size and SSD use, but it does not establish a universal heap figure or an across-the-board SSD recommendation. Choose heap and storage based on the dataset, workload, and environment you will operate; use measurements from that environment rather than treating a generic number as a TDB requirement. Apache Jena TDB FAQ
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