TDB Configuration

There are a number of configuration options that affect the operation of TDB.

Contents

Setting Options

Options can be set globally, through out the JVM, or on a per query execution basis. TDB uses the same mechanism as ARQ.

There is a global context, which is give to each query query execution as it is created. Modifications to the global context after the query execution is created are not seen by the query execution. Modifications to the context of a single query execution do not affect any other query execution nor the global context.

A context is a set of symbol/value pairs. Symbols are used created internal to ARQ and TDB and accessed via Java constants. Values are any Java object, together with the values true and false, which are short for the constants of class java.lang.Boolean.

Setting globally:

 TDB.getContext().set(symbol, value) ;

Per query execution:

 try(QueryExecution qExec = QueryExecutionFactory.create(...)) {
     qExec.getContext().set(symbol, value) ;
     ...
 }

Setting for a query execution happens before any query compilation or setup happens. Creation of a query execution object does not compile the query, which happens when the appropriate .exec method is called.

Setting from the command line

Options can also set from the command line with "--set.

Setting with Java System properties

(TDB 0.8.5 and later)

Options can be set when invoking the JVM using the Java system properties as set by "-D".

Query of the union of named graphs

See TDB/Datasets.

Logging Query Execution

If the symbol "tdb:logExec" is set to "true", and also the logger org.apache.jena.tdb.exec is enabled fro level "info", then each basic graph patterns is logged before execution. This pattern logged is after substitution of variable values and after optimization by the BGP optimizer.

Dataset Caching

(TDB 0.8.0 and later)

TDB caches datasets based on the location of the backing directory. Within a single JVM, all attempts to create or open a dataset at a particular location go through the same dataset (and same disk caching). Therefore, an application can open the same location several times in different places in the code and still get the same underlying dataset for query and update.

Note that closing the dataset closes it everywhere (the opening calls are not being reference counted).

File Access Mode

The context symbol can be set to "mapped" or "direct". Unset, or the value "default", ask TDB to use to make the choice based on JVM. Leaving it to the default is strongly encouraged.

TDB Configuration Symbols

Configuration Symbols

Symbol Java Constant Effect Default
tdb:logExec TDB.symLogExec Log execution of BGPs. Set to "true" to enable. Must also enable the logger "org.apache.jena.tdb.exec". e.g. log4j.properties log4j.logger.org.apache.jena.tdb.exec=INFO unset
tdb:unionDefaultGraph TDB.symUnionDefaultGraph Query patterns on the default graph match against the union of the named graphs. unset
tdb:fileMode SystemTDB.fileMode Force use of memory mapped files ("mapped") or direct file caching ("direct"). See discussion of TDB on 32 or 64 bit hardware, especially limitations of memory mapped files on 32 bit Java. Set by the system based on 32 or 64 bit java.

Advanced Store Configuration

Various internal caching sizes can be set to different values to the defaults. See the full description.