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Techday2010 Postgresql9
 

Techday2010 Postgresql9

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PostgreSQL 9 presentation for the Technology Day event (2010) inside 1&1.

PostgreSQL 9 presentation for the Technology Day event (2010) inside 1&1.

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    Techday2010 Postgresql9 Techday2010 Postgresql9 Presentation Transcript

    • What‘s new in PostgreSQL 9 Dan-Claudiu DRAGOŞ
    • PostgreSQL 9 About PostgreSQL• This presentation was inspired by the sessions I‘ve attended at Fosdem 2010• PostgreSQL means: – Standards followed closely – A true relational database – Complex, advanced features that puts it far ahead of its competition – The best tool to use for advanced database-based applications!• This comes at a cost: it can‘t compete with simpler database systems on poor hardware and writing „simple things“ tends to get harder 2
    • PostgreSQL 9 Common Table Expressions• Available since version 8.4• They are about defining an in-place data structure by the result of a query or a query combination• This data structure can then be queried further• Recursive join over this data structure is also possible• Some of this functionality was available before by using: • Views (named data structures stored into the database backend) • Subselects• The join recursion is a brand new feature 3
    • PostgreSQL 9 Common Table Expressions• Basic usage WITH [RECURSIVE] name AS ( SELECT field1 FROM table WHERE field2=“abc” ) SELECT * FROM name ORDER BY field; 4
    • PostgreSQL 9 Common Table Expressions• Join recursion – Assume we have the following corporate structure: -- department structure represented here is as follows: -- -- ROOT-+->A-+->B-+->C -- | | -- | +->D-+->F -- +->E-+->G – We want all the departments under A (or under any department, actually) 5
    • PostgreSQL 9 Common Table Expressions• Join recursion CREATE TABLE department ( id INTEGER PRIMARY KEY, parent_department INTEGER REFERENCES department, name TEXT ); INSERT INTO department (id, parent_department, "name") VALUES (0, NULL, ROOT), (1, 0, A), (2, 1, B), (3, 2, C), (4, 2, D), (5, 0, E), (6, 4, F), (7, 5, G); 6
    • PostgreSQL 9 Common Table Expressions• Join recursion WITH RECURSIVE subdepartment AS ( -- non-recursive term SELECT * FROM department WHERE name = A UNION ALL -- recursive term SELECT d.* FROM department AS d JOIN subdepartment AS sd ON (d.parent_department = sd.id) ) SELECT * FROM subdepartment ORDER BY name; 7
    • PostgreSQL 9 Common Table Expressions• Join recursion – The non-recursive term is optional – There are some restrictions when it comes to defining the recursive term: – No subquery using the recursive term (no double recursion) – No aggregate functions such as COUNT(*) – No HAVING, GROUP BY – No ORDER BY, no LIMIT – No FULL JOIN – The recursive term must be on the left hand side: » JOIN reference ON (recursiveterm.field = reference.field)• The database engine performs a brute-force, all-terms comparison so performance can sometimes be an issue 8
    • PostgreSQL 9 Hot Standby and Streaming Replication• They are both about database synchronization• Hot Standby is a „push“• Streaming Replication is a „pull“• The issue at hand is duplicating the contents of a Master Database into one or more Slaves• Hot Standby means that every query ran on Master is also ran on the Slave; this also works for table locks!• Streaming replication means that every database transaction is requested by the Slave and then applied on it 9
    • PostgreSQL 9 Deferrable Unique Constraints• This query sequence always fails:# CREATE TABLE test (a INT PRIMARY KEY);# INSERT INTO test values (1), (2);# UPDATE test SET a = a + 1; ERROR: duplicate key value violates unique constraint "test_pkey" DETAIL: Key (a)=(2) already exists.• What 9.0 version provides is that the uniqueness constraint may be checked after running the query, not as the query runs:# CREATE TABLE test (a INT PRIMARY KEY DEFERRABLE); 10
    • PostgreSQL 9 Exclusion Constraints• Before 9.0, exclusion would be checked by using operator “=“• Version 9.0 allows for a more complex approach# CREATE TABLE reservation ( room TEXT, speaker TEXT, during PERIOD); ALTER TABLE reservation ADD CONSTRAINT test_exclude EXCLUDE USING gist (room WITH =,during WITH &&);• The constraint is defined on 2 fields; the point is not having the same room reserved at the same time• The example uses 2 modules from „contrib“ (temporal and gist) 11
    • PostgreSQL 9 Exclusion Constraints• Example using the previous table definition:# INSERT INTO reservation (speaker ,room, during) VALUES ( ‘Dan, ‘Flex Room, period(2010-12-10 12:00:00, 2010-12-10 13:00:00)); INSERT 0 1# INSERT INTO reservation (speaker, room, during) VALUES ( ‘Catalin, ‘Presentation, period(2010-12-10 15:00:00, 2010-12-10 16:00:00)); INSERT 0 1# INSERT INTO reservation (speaker ,room, during) VALUES ( ‘Andrei, ‘Flex Room, period(2010-12-10 12:30:00, 2010-12-10 13:00:00)); ERROR: conflicting key value violates exclusion constraint "test_exclude" DETAIL: Key (room, during)=(Flex Room, [2010-12-10 12:30:00+02, 2010-12- 10 13:00:00+02)) conflicts with existing key (room, during)=(Flex Room, [2010-12-10 12:00:00+02, 2010-12-10 13:00:00+02)).• This feature is available in PostgreSQL only 12
    • Smaller enhancements• GRANT / REVOKE on Schemas – PostgreSQL has Databases -> Schemas -> Tables -> Fields – Until 9.0 you could grant (revoke) rights on Databases and Tables only – This functionality could be achieved before 9.0 by writing a script• Faster VACUUM FULL – This is the more or less equivalent to the OPTIMIZE query in MySQL – This command used to be pretty slow on large databases – In 9.0 it works by performing a copy of the database• Better 64bit support – 64bit binaries were already available on Linux – Windows native 64bit binary is the new thing in version 9.0 13
    • PL/PgSQL enhancements• Unnamed functions – In 9.0 you can run code snippets in place – Before 9.0 you had to define a stored procedure and then call it DO language plpgsql $$ DECLARE vr record; BEGIN FOR vr IN SELECT tablename FROM pg_tables WHERE tableowner = ‘dan AND schemaname NOT IN (pg_catalog,information_schema) LOOP EXECUTE GRANT SELECT ON || vr.tablename || TO tester; END LOOP; END $$; 14
    • PL/PgSQL enhancements• Named parameter calls – Before 9.0 you had to provide all the function parameters and care for their order, as provided in the function definition – Version 8.4 added “default parameters”, allowing skipping certain parameters (they would be replaced with their default values) – Example function: CREATE FUNCTION test (a INT, b TEXT) RETURNS TEXT AS $$ DECLARE value TEXT; BEGIN value := a is || a::text || and b is || b; RETURN value; END; $$ LANGUAGE plpgsql; 15
    • PL/PgSQL enhancements• Named parameter calls – Before 9.0 you would have called it this way: SELECT test(1,foo); test ------------------------- a is 1 and b is foo (1 row) – Version 9.0 allows this type of function call: SELECT test( b:=foo, a:=1); test ------------------------- a is 1 and b is foo (1 row) 16
    • That’s it• Questions? 17