SQL/MED: Doping for PostgreSQL
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SQL/MED is Management of External Data, a part of the SQL standard that deals with how a database management system can integrate data stored outside the database. The implementation of this specification has begun in PostgreSQL 8.4 and will over time introduce powerful new features into PostgreSQL.
![Another Wrapper Interface Example
Possible setup for accessing HTML tables stored in a web site
as SQL tables:
CREATE FOREIGN DATA WRAPPER htmlfile
LIBRARY 'html_fdw.so'
LANGUAGE C;
CREATE SERVER intranetweb
FOREIGN DATA WRAPPER htmlfile
OPTIONS (baseurl 'http://intranet/data');
CREATE FOREIGN TABLE data
SERVER intranetweb
OPTIONS (path 'foo.html#//table[@id="table1"]');](https://image.slidesharecdn.com/homepeterreferencepresentations2009-pgcon-sqlmedsqlmed-090619040448-phpapp02/85/SQL-MED-Doping-for-PostgreSQL-16-320.jpg)
![Routine Mappings
Routine mappings: passing a function/procedure through to a
foreign server
CREATE ROUTINE MAPPING <routine mapping name>
FOR <specific routine designator>
SERVER <foreign server name>
[ <generic options> ];](https://image.slidesharecdn.com/homepeterreferencepresentations2009-pgcon-sqlmedsqlmed-090619040448-phpapp02/85/SQL-MED-Doping-for-PostgreSQL-17-320.jpg)
![Example: Simple DATALINK Type
CREATE TABLE persons (
id integer,
name text,
picture DATALINK [NO LINK CONTROL]
);
INSERT INTO persons VALUES (
1,
'Jon Doe',
DLVALUE('file://some/where/1.jpg')
);
SQL specifies support for file: and http:.
This variant doesn’t do anything except store URLs.](https://image.slidesharecdn.com/homepeterreferencepresentations2009-pgcon-sqlmedsqlmed-090619040448-phpapp02/85/SQL-MED-Doping-for-PostgreSQL-27-320.jpg)
![[Android] Data Storage](https://cdn.slidesharecdn.com/ss_thumbnails/trainingandroidlesson7-130304083333-phpapp02-thumbnail.jpg?width=560&fit=bounds)
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SQL/MED: Doping for PostgreSQL
- 1. SQL/MED Doping for PostgreSQL Peter Eisentraut Senior Software Engineer Lab Development F-Secure Corporation PGCon 2009
- 2. SQL/MED: Management of External Data MED = Management of External Data Methods to access data stored outside the database system through normal SQL SQL/MED is ISO/IEC 9075-9
- 3. Applications and Use Cases Connect to other DBMS (like DBI-Link) Other primary data storage: Oracle, MySQL, . . . Data warehouses etc.: Greenplum, Truviso, . . . Connect to other PostgreSQL instances (like dblink) Read non-SQL data Files: CSV, XML, JSON, . . . File systems: Google FS, Hadoop FS, Lustre, . . . Databases: CouchDB, BigTable, NDB, S3, . . . (“Cloud” stuff) Memcache Clustering, partitioning (think PL/Proxy) Manage data stored in file system Images Video Engineering data
- 4. Applications and Use Cases Connect to other DBMS (like DBI-Link) Other primary data storage: Oracle, MySQL, . . . Data warehouses etc.: Greenplum, Truviso, . . . Connect to other PostgreSQL instances (like dblink) Read non-SQL data Files: CSV, XML, JSON, . . . File systems: Google FS, Hadoop FS, Lustre, . . . Databases: CouchDB, BigTable, NDB, S3, . . . (“Cloud” stuff) Memcache Clustering, partitioning (think PL/Proxy) Manage data stored in file system Images Video Engineering data
- 5. Why do we care? Unifies existing ad-hoc solutions. Powerful new functionality Makes PostgreSQL the center of data management. Implementation has begun in PostgreSQL 8.4. Several people have plans for PostgreSQL 8.5. See status report later in this presentation.
- 6. Advantages Schema integration All data appears as tables. Access control Use GRANT/REVOKE for everything. Standard APIs Mix and share. Centralized control Manage all data through the DBMS.
- 7. Implications for Application Design and Deployment Before application application application application application MySQL MySQL PostgreSQL file system Oracle Cluster
- 8. Implications for Application Design and Deployment After application application application application application PostgreSQL MySQL MySQL file system Oracle CouchDB Cluster
- 9. The Two Parts of SQL/MED Wrapper interface Access other data sources, represent them as SQL tables Datalinks Manage files stored in file system, represent file references as column values
- 10. Wrapper Interface Concepts Define a foreign table . . . On a foreign server . . . Accessed through a foreign-data wrapper
- 11. Wrapper Interface Concepts Define a foreign table . . . think: a dblink view On a foreign server . . . think: dblink_connect Accessed through a foreign-data wrapper think: dblink.so library
- 12. Foreign-Data Wrappers Foreign-data wrapper (FDW): a library that can communicate with external data sources CREATE FOREIGN DATA WRAPPER foosql LIBRARY 'foosql_fdw.so' LANGUAGE C; PostgreSQL communicates with foosql_fdw.so using SQL/MED FDW API. foosql_fdw.so communicates with FooSQL server using their own protocol. In theory, FooSQL, Inc. would ship foosql_fdw.so with their product. In practice, this is not so wide-spread.
- 13. Foreign Servers Foreign server: an instance of an external data source accessed through a FDW CREATE SERVER extradb FOREIGN DATA WRAPPER foosql OPTIONS (host 'foo.example.com', port '2345'); Options depend on FDW.
- 14. User Mappings User mapping: additional user-specific options for a foreign server CREATE USER MAPPING FOR peter SERVER extradb OPTIONS (user 'peter', password 'seKret'); Options depend on FDW. Putting connection options into server vs. user mapping is a matter of convention or convenience.
- 15. Foreign Tables Foreign table: a table stored on a foreign server CREATE FOREIGN TABLE data SERVER extradb OPTIONS (tablename 'DATA123'); Now you can read and write the table as if it were local (depending on FDW features/implementation). Options specified for FDW, server, and user mapping are used as connection parameters (depending on FDW).
- 16. Another Wrapper Interface Example Possible setup for accessing HTML tables stored in a web site as SQL tables: CREATE FOREIGN DATA WRAPPER htmlfile LIBRARY 'html_fdw.so' LANGUAGE C; CREATE SERVER intranetweb FOREIGN DATA WRAPPER htmlfile OPTIONS (baseurl 'http://intranet/data'); CREATE FOREIGN TABLE data SERVER intranetweb OPTIONS (path 'foo.html#//table[@id="table1"]');
- 17. Routine Mappings Routine mappings: passing a function/procedure through to a foreign server CREATE ROUTINE MAPPING <routine mapping name> FOR <specific routine designator> SERVER <foreign server name> [ <generic options> ];
- 18. Routine Mappings Examples Example like PL/Proxy: CREATE ROUTINE MAPPING myfunc(a int, b text) SERVER plproxydb OPTIONS (cluster 'somecluster', runon 'hashtext(a)'); Example XML-RPC: CREATE ROUTINE MAPPING process(data xml) SERVER xmlrpc OPTIONS (request '<methodCall>...</methodCall>');
- 19. Wrapper Interface Access Control GRANT USAGE ON FOREIGN DATA WRAPPER GRANT USAGE FOREIGN SERVER Foreign tables and routines have regular privileges. Passwords for remote access can be managed via user mappings. Front-to-end Kerberos or SSL support could be cool.
- 20. Importing Foreign Schemas Automatically create foreign tables based on tables available remotely. IMPORT FOREIGN SCHEMA someschema LIMIT TO (tab1, tab2, tab2) FROM SERVER extradb INTO myschema; (SQL standard doesn’t support foreign routine import.)
- 21. Status of SQL/MED in PostgreSQL 8.4 PostgreSQL 8.4 has: CREATE FOREIGN DATA WRAPPER, but no library support CREATE SERVER CREATE USER MAPPING ACL support Doesn’t really do anything :-( Plans for PL/Proxy to store connection information
- 22. Status of SQL/MED Elsewhere IBM DB2 provides a full implementation. MySQL and Farrago use some syntax elements. No other known implementations. Some vendors have had their custom remote access functionality.
- 23. Plan & Issues PostgreSQL 8.5 and beyond . . . Write wrapper library and foreign table support Supply a few foreign-data wrapper libraries Use standard wrapper interface API or design our own API? Optimizations, e. g., passing query qualifications to foreign servers Distributed transactions Needs careful security evaluation (remember dblink issues)
- 24. Plan & Issues PostgreSQL 8.5 and beyond . . . Write wrapper library and foreign table support Supply a few foreign-data wrapper libraries Use standard wrapper interface API or design our own API? Optimizations, e. g., passing query qualifications to foreign servers Distributed transactions Needs careful security evaluation (remember dblink issues)
- 25. Datalink Concepts Files are referenced through a new DATALINK type Database system has control over external files No need to store file contents in database system Access control and integrity mechanisms of DBMS can be extended to file system
- 26. Datalink Use Cases Certain types of data are primarily uses as files with external applications. Handling very large files (e. g., video) by DBMS is inefficient Use of distributed files systems Handle files stored on web server, FTP server, etc.
- 27. Example: Simple DATALINK Type CREATE TABLE persons ( id integer, name text, picture DATALINK [NO LINK CONTROL] ); INSERT INTO persons VALUES ( 1, 'Jon Doe', DLVALUE('file://some/where/1.jpg') ); SQL specifies support for file: and http:. This variant doesn’t do anything except store URLs.
- 28. DATALINK Attributes: Link and Integrity Control NO LINK CONTROL Datalink value need not reference an existing file/URL. FILE LINK CONTROL Datalink value must reference an existing file/URL. INTEGRITY ALL Referenced files can only be renamed or deleted through SQL. INTEGRITY SELECTIVE Referenced files can be renamed or deleted through SQL or directly. INTEGRITY NONE (implied for NO LINK CONTROL)
- 29. DATALINK Attributes: Unlinking and Recovery Behavior ON UNLINK DELETE File is deleted from file system when deleted from database. ON UNLINK RESTORE File’s original permissions are restored when deleted from database. ON UNLINK NONE No change in file permissions when file reference is deleted from database. RECOVERY YES PITR applies to referenced files. RECOVERY NO PITR does not apply to referenced files.
- 30. DATALINK Attributes: Access Permissions READ PERMISSION FS File system controls file read permission. READ PERMISSION DB Database system controls file read permission. WRITE PERMISSION FS File system controls file write permission. WRITE PERMISSION ADMIN Writes to the file are managed by the database system. WRITE PERMISSION BLOCKED Writing to file is blocked.
- 31. How to Implement Datalinks Implementation challenges: OS-dependent File-system dependent Application-dependent Possibilities: Kernel modules LD_PRELOAD Extended FS attributes Lots of hocus pocus Don’t hold your breath.
- 32. Summary SQL/MED Wrapper interface Datalinks Substantial support planned for PostgreSQL 8.5 and beyond Further reading: http://wiki.postgresql.org/wiki/SqlMedConnectionManager (Martin Pihlak) http://www.sigmod.org/record/issues/0103/JM-Sta.pdf (Jim Melton et al.) http://www.sigmod.org/record/issues/0209/jimmelton.pdf (Jim Melton et al.) ISO/IEC 9075-9:2008 (“SQL/MED”)
- 33. Rights and Attributions This presentation “SQL/MED: Doping for PostgreSQL” was authored by Peter Eisentraut and is licensed under the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported license. The image on page 2 is from the Open Clip Art Library and is in the public domain. The image on page 5 is from the Open Clip Art Library and is in the public domain. The image on page 9 is “The fork in the road” by Flickr user i_yudai, available under the Creative Commons Attribution 2.0 Generic license. The image on page 31 is “Fork in a Steve” by Flickr user morgantepsic, available under the Creative Commons Attribution-Share Alike 2.0 Generic license.