This page describe the configuration options available. These are options for query processing, not for the database layout and storage, which is controlled by store descriptions.
Options can be set globally, through out the JVM, or on a per query execution basis. SDB 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 SDB and access 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:
SDB.getContext().set(symbol, value) ;
Per query execution:
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.
| Symbol | Effect | Default |
|---|---|---|
SDB.unionDefaultGraph |
Query patterns on the default graph match against the union of the named graphs. | false |
SDB.jdbcStream |
Attempt to stream JDBC results. | true |
SDB.jdbcFetchSize |
Set the JDBC fetch size on the SQL query statements. Must be >= 0. | unset |
SDB.streamGraphAPI |
Stream Jena APIs (also requires jdbcStream and jdbcFetchSize |
false |
SDB.annotateGeneratedSQL |
Put SQL comments in SQL | true |
All the named graphs can be treated as a single graph in two ways:
either set the SDB option above or use the URI that refers to RDF
merge of the named graphs (urn:x-arq:UnionGraph).
When querying the RDF merge of named graph, the default graph in the store is not included.
This feature applies to queries only. It does not affect the storage nor does it change loading.
To find out which named graph a triple can be found in, use GRAPH
as usual.
The following special IRIs exist for use as a graph name in GRAPH
only:
<urn:x-arq:DefaultGraph> – the default graph, even when
option for named union queries is set.<urn:x-arq:UnionGraph> – the union of all named graphs, even
when the option for named union queries is not set.By default, SDB processes results from SQL statements in a streaming fashion. It is important to close query execution objects, especially if not consuming all the results, because that causes the underlying JDBC result set to be closed. JDBC result sets can be a scarce system resource.
If this option is set, but the JDBC connection is not streaming, then this feature is harmless. Setting it false caused SDB to read all results of an SQL statement at once, treating streamed connections as unstreamed.
Note that this only streams results end-to-end if the underlying JDBC connection itself is set up to stream. Most do not in the default configuration to reduce transient resource peaks on the server under load.
Setting the fetch size enables cursors in some databases but there may be restrictions imposed by the database. See the documentation for your database for details.
In addition, operations on the graph API can be made streaming by also setting the Graph API to streaming.
SQL generation can include SQL comments to show how SPARQL has been
turned into SQL. This option is true by default and always set
for the command sdbprint.
SDB.getContext().setFalse(SDB.annotateGeneratedSQL) ;