2.3.0

Release date: 2026-01-28

Enhancements

  • Removed librdf dependency: The extension no longer depends on the Redland RDF Library (librdf). RDF/XML parsing for DESCRIBE queries is now performed using only libxml2, reducing external dependencies and improving maintainability.

  • Support to data modification queries: Introduced per-row SPARQL INSERT DATA, DELETE DATA, and UPDATE operations via the sparql_update_pattern option on foreign tables. The addition of the batch_size parameter enables efficient batching of these operations, significantly improving performance for bulk modifications.

  • Enhanced error handling in ExecuteSPARQL: Improved the handling of HTTP errors by capturing and displaying detailed error messages from the SPARQL endpoint. This includes disabling CURLOPT_FAILONERROR to capture response bodies for HTTP errors, adding specific error messages for common HTTP status codes (e.g., 400, 401, 404, 500).

Breaking Changes

  • The sparql.describe() function no longer accepts the raw_literal parameter. Users who need to extract plain text from literals can use the sparql.lex() function instead. This simplifies the function signature and encourages a more consistent approach to handling RDF literals.

  • The sparql.regex function is no longer available for local evaluation in PostgreSQL, as it turned out that its semantics cannot be reliably reproduced locally. Queries relying on local evaluation of sparql.regex will now fail with an error.

Minor Changes

  • The log_sparql option for foreign tables now defaults to false. Since INSERT, UPDATE, and DELETE operations can generate large SPARQL queries, enabling this option by default could result in unnecessarily large log entries.

Bug Fixes

  • Fixed URIs and blank nodes being incorrectly handled as plain literals in InsertRetrievedData() (used by rdf_fdw_clone_table()). When cloning foreign tables with rdfnode columns, URIs were being treated as plain text instead of being wrapped in angle brackets (e.g., <http://example.com>), and blank nodes were missing the _: prefix. The fix now checks the target column type: for rdfnode columns, it properly formats URIs with <> and blank nodes with _:, while for standard PostgreSQL types it extracts only the raw content. This ensures correct round-trip behavior when materializing RDF data into ordinary tables.

  • Fixed failure when extracting content from empty RDF literals in InsertRetrievedData(). The code was incorrectly using xmlNodeDump() to serialize RDF term nodes, which included XML tags in the output (e.g., <literal datatype="...">value</literal>). This caused rdf_fdw_clone_table() calls on columns containing empty literals (e.g., "", ""@en, or ""^^xsd:string) to fail. Now uses xmlNodeGetContent() to extract only the text content without XML tags, properly handling empty and non-empty RDF term nodes alike.

  • Fixed critical bug in all date comparison operators (>, >=, <, <=, =, !=) between rdfnode and PostgreSQL date types. Previously, the code used the wrong macro (PG_GETARG_INT16) to retrieve date arguments, causing all local date comparisons to fail or behave unpredictably. Now uses the correct PG_GETARG_DATEADT macro and adds robust error handling for non-date values. This ensures correct filtering and pushdown of date conditions, especially for queries like WHERE col > '1900-01-30'::date.

  • Fixed a bug in sparql.hours(rdfnode), sparql.minutes(rdfnode), and sparql.seconds(rdfnode) where RDF nodes containing only xsd:time were not handled correctly. These functions now properly extract the hour, minute, and second from both xsd:dateTime and xsd:time typed RDF nodes, instead of assuming all values are xsd:dateTime.

  • Updated sparql.concat() function to comply with SPARQL 1.1: now returns a simple literal (no language tag or datatype) when concatenating literals with conflicting language tags or incompatible datatypes, instead of throwing an error.

  • Empty RDF literals incorrectly returned as NULL: Fixed a bug where empty RDF literals (e.g., "", ""@en, or ""^^xsd:string) were being incorrectly returned as SQL NULL values instead of empty strings. The issue occurred in CreateTuple() where xmlNodeGetContent() returns NULL for empty XML elements. The fix now properly distinguishes between empty RDF terms (valid empty strings) and unbound SPARQL variables (SQL NULL) by checking the XML element type (<literal>, <uri>, or <bnode>).

  • Literals with escaped quotes corrupted during round-trip: Fixed a critical bug where literals containing escaped quotes (e.g., "\"WWU\""@en) were being corrupted when retrieved from SPARQL results. The CreateTuple() function was incorrectly reparsing raw XML text content as RDF syntax, causing quote characters to be interpreted as literal delimiters rather than data. This has been fixed by constructing rdfnode values directly from raw lexical content and manually appending language tags or datatypes.

  • Control characters not properly escaped in SPARQL statements: Control characters (newlines, tabs, carriage returns) in literals are now properly escaped in SPARQL INSERT and DELETE statements, ensuring correct round-trip behavior.

  • DESCRIBE queries with large result sets caused severe performance degradation: Fixed a critical performance issue where sparql.describe() queries returning large result sets took too long to complete. The root cause was in DescribeIRI(), which used librdf_parser_parse_string_into_model() to build a complete in-memory RDF graph model before extracting triples. This has been replaced with librdf_parser_parse_string_as_stream(), which processes RDF/XML on-the-fly without constructing an intermediate graph database. This dramatically reduces memory footprint and brings DESCRIBE query performance in line with SELECT queries handling similar-sized result sets.

  • UCASE and LCASE functions failed to convert multibyte UTF-8 characters: Fixed a bug where sparql.ucase() and sparql.lcase() were only converting ASCII characters (a-z, A-Z) and leaving multibyte UTF-8 characters unchanged. For example, sparql.ucase('"Westfälische Wilhelms-Universität Münster"@de') would incorrectly return "WESTFäLISCHE WILHELMS-UNIVERSITäT MüNSTER"@de instead of properly uppercasing ä, ö, ü to Ä, Ö, Ü. The functions now use PostgreSQL’s built-in upper() and lower() functions with proper collation support, correctly handling all Unicode characters according to the database’s locale settings.

  • SUBSTR function failed for multibyte UTF-8 characters and empty inputs: Fixed a bug in sparql.substr() where it incorrectly counted bytes instead of characters for multibyte UTF-8 strings, leading to truncated results. Additionally, the function now correctly returns an empty string when the start position is beyond the string length, instead of throwing an error.

  • Malformed SPARQL with FILTER(NULL) in older PostgreSQL versions: Fixed a bug in PostgreSQL 9.5 where NULL constants in expressions were being deparsed as the literal string “NULL” instead of returning a NULL pointer. This caused malformed SPARQL queries like FILTER(NULL) to be generated. The fix ensures that NULL constants are properly handled by preventing pushdown of such expressions.

  • Fixed unexpected behavior in sparql.bnode() where passing an already-formatted blank node (e.g., _:bnode1) would return SQL NULL instead of handling it gracefully. The function now implements idempotent behavior: if the input is already a blank node, it returns it as-is.

  • Fixed a bug where local filters (WHERE clauses) that were pushed down were also being evaluated locally, which was just redundant. Now, only conditions that cannot be pushed down are evaluated locally by PostgreSQL, ensuring correct results for non-pushable foreign tables.

2.2.0

Release date: 2025-12-07

Enhancements

  • SPARQL aggregate functions:

    Added support for SPARQL-style aggregate functions sparql.sum, sparql.avg, sparql.min, sparql.max, sparql.group_concat, and sparql.sample in SQL queries. These functions are now fully implemented and can be used for local aggregation in PostgreSQL, improving compatibility with SPARQL semantics and enabling more expressive analytics on RDF data. Aggregate pushdown to the SPARQL endpoint is not yet supported; all aggregation is performed locally by PostgreSQL.

  • Enhanced version information:

    The rdf_fdw_version() function now returns a comprehensive version string that includes PostgreSQL version, compiler information, and all dependency versions (libxml, librdf, libcurl) in a single formatted output. A new rdf_fdw_settings() function provides extended dependency information including optional components like SSL, zlib, libSSH, and nghttp2. The rdf_fdw_settings view parses this extended information into a table format for convenient programmatic access to individual component versions.

  • Improved EXPLAIN diagnostics for Foreign Scan nodes:

    EXPLAIN output now include rdf_fdw-specific details for each Foreign Scan node, showing which SQL clauses are pushed down to the remote SPARQL endpoint. The plan displays lines such as Pushdown: enabled/disabled, Remote Filter, Remote Sort Key, Remote Limit, and Remote Select, making it easier to understand query translation and pushdown behavior.

Bug Fixes

  • Fix lex() to correctly handle doubled-quote escapes in literals.

    RDF literals containing double-quotes were being truncated, leading to invalid results of sparql.lex() or any function that depends on it. This has now being fixed.

2.1.0

Release date: 2025-09-25

Enhancements

  • SPARQL Prefix Management:

    rdf_fdw now includes built-in support for SPARQL prefix management via a structured catalog and helper functions. This feature introduces:

    prefix_contexts: Named groups of reusable SPARQL prefixes.

    prefixes: Individual prefix → URI mappings associated with a context.

    A suite of SQL functions to add, update, delete, and override contexts and prefixes. This enhancement simplifies query generation, reduces redundancy, and makes SPARQL integration more maintainable — especially when dealing with multiple endpoints or vocabularies.

  • Add enable_xml_huge server option to support large XML result sets

    The new enable_xml_huge option allows users to enable libxml2’s XML_PARSE_HUGE flag when parsing SPARQL result sets. This is useful for consuming large XML responses that exceed libxml2’s default safety limits. By default, this option is disabled for security reasons.

Bug Fixes

  • NULL RDFNodes:

    This fixes a bug that could potentially lead the system to crash if the triple store returns a NULL value for an specific node (edge case).

  • xmlParseMemory errors

    An issue has been resolved where the system could potentially crash if libxml2 failed to parse a given XML string (for example, due to an out-of-memory error). A check has been added to detect and prevent such crashes.

  • xmlDocGetRootElement failing to get the root element

    A safeguard has been introduced to handle cases where xmlDocGetRootElement fails to parse the root node of an XML document. Instead of proceeding with an empty set, an error message is now displayed to inform the user of the issue.

2.0.0

Release date: 2025-05-22

This is a major release of rdf_fdw featuring substantial new features, improved standards compliance, and important infrastructure enhancements. Backward compatibility is preserved, but users are encouraged to review the new features and updated behavior.

Enhancements

  • PostgreSQL 9.5 and 18 (in beta1 as of this release) support.
  • SPARQL DESCRIBE query support via the new sparql.describe() support function.
  • New rdfnode data type, enabling:
    • Representation of RDF literals and IRIs with full lexical fidelity.
    • Precise round-tripping of SPARQL values within SQL.
    • Equality and order comparisons with native PostgreSQL types (e.g., int, float, text, date).
  • SPARQL 1.1 Built-in Function Support via SQL queries.

    These functions are translated to their SPARQL equivalents when pushed down to the foreign data wrapper.

Minor Changes

  • The FOREIGN TABLE option log_sparql is now set to true, if omitted. If you don’t want to log the SPARQL query, consider using ALTER FOREIGN TABLE to disable this option manually, e.g.
  ALTER FOREIGN TABLE myrdftable OPTIONS (ADD log_sparql 'false');

Bug Fixes

  • Query cancellation support:

    Added CHECK_FOR_INTERRUPTS() in key execution points to allow PostgreSQL backends to detect user-initiated query cancellations (e.g., Ctrl+C), improving long-running query handling.

External Libraries

  • Added a new dependency: Redland RDF Library (librdf) — used for parsing and serializing RDF data, and supporting DESCRIBE queries.

1.3.0

Release date: 2024-09-30

Enhancements

  • Support for PostgreSQL 9.6, 10, and 17: This adds support for the long EOL’d PostgreSQL versions 9.6 and 10. It is definitely discouraged to use these unsupported versions, but in case you’re for whatever reason unable to perform an upgrade you can now use the rdf_fdw.

1.2.0

Release date: 2024-05-22

Enhancements

  • Pushdown support for Math, String and Date/Time functions:
    • abs, ceil, floor, round
    • length, upper, lower, starts_with, substring, md5
    • extract(year from x), extract(month from x), extract(year from x), extract(hour from x), extract(minute from x), extract(second from x)
    • date_part(year, x), date_part('month',x), date_part('year', x), date_part('hour', x), date_part('minute', x), date_part('second', x)

    When used in the WHERE clause these functions will be translated to their correspondent SPARQL FILTER expressions.

Bug Fixes

  • Bug fix for WHERE conditions with “inverted” arguments - that is, value in the left side (T_Const) and column in the right side (T_Var): This fixes a bug that led the pushdown of WHERE condiditions containing “inverted” arguments to fail, e.g "foo" = column, 42 > column. Now the order of T_Const and T_Var in the arguments is irrelevant.

1.1.0

Release date: 2024-04-10

Enhancements

  • USER MAPPING support: This feature defines a mapping of a PostgreSQL user to an user in the target triplestore - user and password, so that the user can be authenticated. Requested by Matt Goldberg.

  • Pushdown suuport for pattern matching operators LIKE and ILIKE: these operators are now translated into SPARQL FILTER expressions as REGEX and pushed down.

  • Enables usage of non-pushable data types in FOREIGN TABLE columns: This disables a check that raised an excepetion when data types that cannot be pushed down were used. This includes non-standard data types, such as geometry or geography from PostGIS.

Bug Fixes

  • Empty SPARQL SELECT clause: This fixes a bug that led some SPARQL queries to be created without any variable in the SELECT clause. We now use SELECT * in case the planner cannot identify which nodes should be retrieved, which can be a bit inefficent if we’re dealing with many columns, but it is much better than an error message.

  • Missing schema from foreign tables in rdf_fdw_clone_table calls: This fixes a bug that led the rdf_fdw_clone_table procedure to always look for the given FOREIGN TABLE in the public schema.

  • xmlDoc* memory leak: The xml document containing the resulst sets from the SPARQL queries wasn’t beeing freed after the query was complete. This led to a memory leak that could potentially cause a system crash once all available memory was consumed by the orphan documents - which is an issue for rather modest server settings that execute mutliple queries in the same session. Reported by Filipe Pessoa.

1.0.0

Release date: 2024-03-15

Initial release.

Support for PostgreSQL 11, 12, 13, 14, 15 and 16.

Main Features

  • Pushdown: LIMIT, ORDER BY, DISTINCT, WHERE with several data types and operators
  • Table copy: This introduces the procedure rdf_fdw_clone_table(), that is designed to copy data from a FOREIGN TABLE into an ordinary TABLE. It provides the possibility to retrieve the data set in batches.
  • Proxy Support for SERVER: quite handy feature in case the PostgreSQL and SPARQL endpoint servers are in different networks and can only communicate through a proxy.