CREATE SERVER virtuoso
FOREIGN DATA WRAPPER rdf_fdw 
OPTIONS (
  endpoint   'http://virtuoso:8890/sparql-auth',
  batch_size '10000');
CREATE FOREIGN TABLE ft (
  subject   rdfnode OPTIONS (variable '?s'),
  predicate rdfnode OPTIONS (variable '?p'),
  object    rdfnode OPTIONS (variable '?o') 
)
SERVER virtuoso OPTIONS (
  log_sparql 'false',
  sparql 'SELECT * { GRAPH <http://rdf-fdw.test/default> {?s ?p ?o} }',
  sparql_update_pattern 
    'GRAPH <http://rdf-fdw.test/default> {
       ?s ?p ?o .
     }'
);
CREATE USER MAPPING FOR postgres
SERVER virtuoso OPTIONS (user 'dba', password 'secret');
/* inserting a large literal (one million characters) */
INSERT INTO ft (subject, predicate, object)
VALUES  ('<https://www.uni-muenster.de>', '<http://www.w3.org/2000/01/rdf-schema#label>', repeat('x', 1000000)::rdfnode);
SELECT subject, predicate, sparql.strlen(object) 
FROM ft;
            subject            |                  predicate                   | strlen  
-------------------------------+----------------------------------------------+---------
 <https://www.uni-muenster.de> | <http://www.w3.org/2000/01/rdf-schema#label> | 1000000
(1 row)

/* updating the large literal (one million characters) */
UPDATE ft SET
  object = repeat('y', 1000000)::rdfnode
WHERE subject = '<https://www.uni-muenster.de>'
  AND predicate = '<http://www.w3.org/2000/01/rdf-schema#label>';
SELECT subject, predicate, sparql.strlen(object) 
FROM ft;
            subject            |                  predicate                   | strlen  
-------------------------------+----------------------------------------------+---------
 <https://www.uni-muenster.de> | <http://www.w3.org/2000/01/rdf-schema#label> | 1000000
(1 row)

/* deleting triple with large literal */
DELETE FROM ft;
/* inserting a one million triples */
INSERT INTO ft (subject, predicate, object)
SELECT '<https://www.uni-muenster.de>', '<http://www.w3.org/2000/01/rdf-schema#label>', i::rdfnode 
FROM generate_series(1,1000000) AS g(i);
ERROR:  bad request on server "virtuoso" (HTTP 400)
DETAIL:  Virtuoso 37000 Error SP031: SPARQL: Internal error: The length of generated SQL text has exceeded 10000 lines of code

SPARQL query:
define sql:big-data-const 0
INSERT DATA { GRAPH <http://rdf-fdw.test/default> {
       <https://www.uni-muenster.de> <http://www.w3.org/2000/01/rdf-schema#label> "1"^^<http://www.w3.org/2001/XMLSchema#int> .
     } };
INSERT DATA { GRAPH <http://rdf-fdw.test/default> {
       <https://www.uni-muenster.de> <http://www.w3.org/2000/01/rdf-schema#label> "2"^^<http://www.w3.org/200... (truncated)
HINT:  Check the SPARQL query syntax.
SELECT * FROM ft
LIMIT 5;
 subject | predicate | object 
---------+-----------+--------
(0 rows)

/* selecting one million triples from the foreign table */
CREATE UNLOGGED TABLE temp_ft AS SELECT * FROM ft;
SELECT count(*) FROM temp_ft;
 count 
-------
     0
(1 row)

SELECT * FROM temp_ft
WHERE 
  subject = '<https://www.uni-muenster.de>'::rdfnode AND
  object BETWEEN 500000::rdfnode AND 500010::rdfnode
ORDER BY object::bigint;
 subject | predicate | object 
---------+-----------+--------
(0 rows)

DROP TABLE temp_ft;
/* cloning one million triples from the foreign table */
CALL
    rdf_fdw_clone_table(
        foreign_table => 'public.ft',
        target_table  => 'public.ft_clone',
        fetch_size => 100000,
        create_table => true,
        verbose => true
    );
INFO:  Target TABLE "public.ft_clone" created based on FOREIGN TABLE "public.ft":

  CREATE TABLE public.ft_clone AS SELECT * FROM public.ft WITH NO DATA;

INFO:  

== Parameters ==

foreign_table: 'ft'
target_table: 'public.ft_clone'
create_table: 'true'
fetch_size: 100000
begin_offset: 0
max_records: 0
ordering_column: 'NOT SET'
ordering sparql variable: '?s'
sort_order: 'ASC'

DROP TABLE ft_clone;
/* describing subject with one million triples */
CREATE UNLOGGED TABLE temp_describe AS
SELECT subject, predicate, object
FROM sparql.describe('virtuoso', 'DESCRIBE <https://www.uni-muenster.de>')
ORDER BY object::bigint;
SELECT count(*) FROM temp_describe;
 count 
-------
     0
(1 row)

SELECT * FROM temp_describe
WHERE 
  subject = '<https://www.uni-muenster.de>'::rdfnode AND
  object BETWEEN 500000::rdfnode AND 500010::rdfnode;
 subject | predicate | object 
---------+-----------+--------
(0 rows)

DROP TABLE temp_describe;
/* deleting a million triples */
DELETE FROM ft;
SELECT * FROM ft;
 subject | predicate | object 
---------+-----------+--------
(0 rows)

DROP SERVER virtuoso CASCADE;
NOTICE:  drop cascades to 2 other objects
DETAIL:  drop cascades to foreign table ft
drop cascades to user mapping for postgres on server virtuoso