Bulk Loading RDF Source Files into one or more Graph IRIs
This document details how large RDF data set files can be bulk loaded into Virtuoso. The data sets may consist of multiple files, which may be loaded into one or several graphs.
- Bulk loading process
- Stopping the bulk load process
- Checking bulk load status
- Cluster-specific details
- Faceted Browser “Entity Label Lookups”
- The Virtuoso Bulk Loader functions must be present. They are pre-loaded starting with commercial version
06.02.3129and open source version
6.1.3, but must be manually loaded into older versions.
- The directory containing the data set files must be included in the **
DirsAllowed**parameter defined in the virtuoso INI file, after which the Virtuoso server must be restarted.
- The Virtuoso Server should be appropriately configured to use sufficient memory and other system resources as detailed in the Virtuoso RDF Performance Tuning Guide, or the load may take an unacceptably long time, approaching forever.
- The file formats and file name extensions of the files to be loaded must be among the following, which the
rdf_loader_run()function understands. Any of these may be compressed in
gzip(i.e., with the additional
.gzfile name extension),
xzcompression formats to save space; in such case, they will be automatically expanded by the bulk loader.
Bulk loading process
The name of the RDF graph into which the data set(s) should be loaded can be specified through a text file placed in the same source directory as the source data files. This file’s contents will override any options specified in the
ld_dir_all()function call. The content of a file with the same name as a data file plus the
.graphfilename extension will be used for that data file (e.g.,
my_data.n3.graphwill be used with
my_data.n3). The content of a file named
global.graphwill be used for any and all other data files in that directory.
Note: if the third parameter (
NULL, any data files that do not have a corresponding
.graphfile will not be loaded.*. If datasets are
TRIGthen the graph name specified in such dataset files in quad format will always be used.
<source-file>.<ext> <source-file>.<ext> .graph global.graph
— e.g., —
myfile.n3 ;; RDF data myfile.n3.graph ;; Contains Graph IRI name into which RDF data from myfile.n3 will be loaded global.graph ;; Contains Graph IRI name into which RDF data from any files that do not have a specific graph name file will be loaded
- Place the graph IRI, , e.g.,
http://dbpedia.org, in the
isqlto register the file(s) to be loaded by running the appropriate function, e.g. –
SQL> ld_dir ('/path/to/files', '*.n3', 'http://dbpedia.org');
ld_dir()**to load only from the specified directory, excluding any subdirectories –
SQL> ld_dir ('<source-filename-or-directory>', '<file name pattern>', 'graph iri');
ld_dir_all()**to load from the specified directory, including any and all subdirectories –
SQL> ld_dir_all ('<source-filename-or-directory>', '<file name pattern>', 'graph iri');
- The table
DB.DBA.load_listcan be used to check the list of data sets registered for loading, and the graph IRIs into which they will be or have been loaded. The **
ll_state**field can have three values: 0 indicating the data set is to be loaded; 1 the data set load is in progress; or 2 the data set load is complete:
SQL> select * from DB.DBA.load_list; ll_file ll_graph ll_state ll_started ll_done ll_host ll_work_time ll_error VARCHAR NOT NULL VARCHAR INTEGER TIMESTAMP TIMESTAMP INTEGER INTEGER VARCHAR _____________________________________________________________________________________________________________________________________ ./dump/d1/file1.n3 http://file1 2 2010.10.20 9:21.18 0 2010.10.20 9:21.18 0 0 NULL NULL ./dump/d2/file2.n3 http://file2 2 2010.10.20 9:21.18 0 2010.10.20 9:21.18 0 0 NULL NULL ./dump/file.n3 http://file 2 2010.10.20 9:21.18 0 2010.10.20 9:21.18 0 0 NULL NULL 3 Rows. -- 1 msec. SQL>
- Finally, perform the bulk load of all data by executing the
rdf_loader_run()function prototype is:
rdf_loader_run ( IN max_files INTEGER := NULL , IN log_enable INT := 2 )
One of the side effects of the default
log_enable = 2 setting is that triggers are disabled, to speed the loading of data. If triggers are required (e.g., for RDF Graph replication between nodes), then the
log_enable mode should be set to 3 when calling the
rdf_loader_run() function as follows:
- Note at the end of the Bulk Load process the
checkpointcommand MUST be run to commit the bulk loaded data to the Virtuoso database file. This is because the default
log_enable = 2mode used by the bulk loader turns off transaction logging, thus if the database is shutdown before a checkpoint is run all the bulk loaded data would be lost. The bulk loader also disables checkpointing and the scheduler, which also need to be re-enabled post bulk load.
checkpoint; checkpoint_interval(N); scheduler_interval(M);
Running multiple Loaders
On a multi-core machine, it is recommended that data sets be split into multiple files, and that these be registered in the
DB.DBA.load_list table with the
ld_dir() function. Once registered for load, the
rdf_loader_run() function can be run multiple times, it is recommended a maximum of no cores / 2.5, to optimally parallelize the data load and hence maximize load speed. A typical script that can be run from command line (e.g.,
bulk_load.sh) might look like –
. /opt/openlink/virtuoso/virtuoso-enterprise.sh isql 1111 dba dba exec="rdf_loader_run();" & isql 1111 dba dba exec="rdf_loader_run();" & isql 1111 dba dba exec="rdf_loader_run();" & isql 1111 dba dba exec="rdf_loader_run();" & isql 1111 dba dba exec="rdf_loader_run();" & isql 1111 dba dba exec="rdf_loader_run();" & isql 1111 dba dba exec="rdf_loader_run();" & wait isql 1111 dba dba exec="checkpoint;"
and be run with the command:
Stopping the bulk load process
- All RDF loader threads can be stopped using the command
rdf_load_stop(), at which point all currently running threads will be allowed to complete and then exit:
Checking bulk load status
- Once the
rdf_loader_run()is complete, you can check the
DB.DBA.load_listto confirm all data sets were loaded successfully. This is indicated by an
2.Note:* The following query can be used to check if any errors occurred when loading datasets file during the bulk load:
select * from DB.DBA.LOAD_LIST where ll_error IS NOT NULL
- On a Virtuoso Clustered Server the “
cl_exec('rdf_ld_srv(log_enable)')” commands (where
3, as with the
rdf_loader_run()function) can be used to invoke a single “
rdf_loader_run()” on each node of the cluster:
SQL> cl_exec('rdf_ld_srv()'); Done. -- 265956 msec. SQL>
Faceted Browser “Entity Label Lookups”
If the Virtuoso Faceted Browser is install its “Entity Label Lookups” table can be automatically updated when new “rdfs:label” entries are added to the database, during bulk load and other insert operations, by adding the new
LabelInferenceName = facets parameter in the “[SPARQL]” section of the
virtuoso.ini config file and restarting the database for it to be picked up.