Demystifying PostgreSQL

Demystifying Presented by Asher Snyder co-founder of www.postgresql.org Latest PostgreSQL version 9.0.1 @ashyboy

What is PostgreSQL? • Completely Open Source Database System – Started in 1995 – Open source project – Not owned by any one company – Controlled by the community – Can’t be bought (Looking at you ORACLE) • ORDMBS – Object-relational database management system? • RDBMS with object-oriented database model – That’s right, it’s not just an RDMBS – You can create your own objects – You can inherit • Fully ACID compliant – Atomicity, Consistency, Isolation, Durability. Guarantees that database transactions are processed reliably. • ANSI SQL compliant

Notable Features • Transactions • Functions (Stored procedures) • Rules • Views • Triggers • Inheritance • Custom Types • Referential Integrity • Array Data Types • Schemas • Hot Standby (as of 9.0) • Streaming Replication (as of 9.0)

Support • Excellent Personal Support! – Vibrant Community • Active Mailing List • Active IRC - #postgres on irc.freenode.net – Absolutely amazing • Complete, Extensive and Detailed Documentation – http://www.postgresql.org/docs/ • Regular and frequent releases and updates – Public Roadmap • Support for older builds – Currently support and release updates to builds as old as 5 years

Support • Numerous Shared Hosts – Such as A2hosting (http://www.a2hosting.com) • Numerous GUI Administration Tools – pgAdmin (http://www.pgadmin.org/) – php pgAdmin (http://phppgadmin.sourceforge.net/) – Notable commercial tools • Navicat (http://www.navicat.com) • EMS (http://sqlmanager.net) – Many many more • http://wiki.postgresql.org/wiki/Community_Guide_to_ PostgreSQL_GUI_Tools

Installation • Despite what you’ve heard Postgres is NOT hard to install On Ubuntu or Debian: $ apt-get install postgresql On Gentoo: $ emerge postgresql Manual Installation: $ adduser postgres mkdir /usr/local/pgsql/data chown postgres /usr/local/pgsql/data su - postgres /usr/local/pgsql/bin/initdb -D /usr/local/pgsql/data /usr/local/pgsql/bin/postgres -D /usr/local/pgsql/data

Installation (cont) • Regardless of what installation method you choose. Make sure to modify postgresql.conf and pg_hba.conf configuration files if you want to allow outside access. pg_hba.conf - Controls which hosts are allowed to connect # TYPE DATABASE USER CIDR-ADDRESS METHOD host all all 0.0.0.0/0 md5 Allows for connection from any outside connection with md5 verification postgresql.conf - PostgreSQL configuration file # - Connection Settings listen_addresses = '*' # IP address to listen on #listen_addresses = 'localhost' # default Allows PostgreSQL to listen on any address

Getting Started pg_hba.conf - Controls which hosts are allowed to connect Start from distro $ /etc/init.d/postgresql start alternatively, you can start it manually $ /usr/local/pgsql/bin/postgres -D /usr/local/pgsql/data

Creating Your Database Launch psql $ psql Create your first PostgreSQL database CREATE DATABASE first_db; Connect to your newly created database c first_db

Tables

Tables - Creating CREATE TABLE users ( "user_id" SERIAL, "email" TEXT, "firstname" TEXT, "lastname" TEXT, "password" TEXT, PRIMARY KEY("user_id") ); • What’s a SERIAL? – Short for INTEGER NOT NULL with default value of nextval('users_user_id_seq') • Similar to AUTO_INCREMENT property of other databases.

Tables - Inserting We can explicitly define each field and the value associated with it. This will set user_id to the default value. INSERT INTO users (email, firstname, lastname, password) VALUES ('asnyder@noloh.com', 'Asher', 'Snyder', 'Pass'); Alternatively, we can not specify the column names and insert based on the column order, using DEFAULT for the user_id. INSERT INTO users VALUES (DEFAULT, 'john@example.com', 'John', 'Doe', 'OtherPass'); Lets see the results SELECT * FROM users; user_id | email | firstname | lastname | password --------+-------------------+-----------+------------------+-----------+---------------------------- 1 | asnyder@noloh.com | Ash | Snyder | Pass 2 | John | Doe | john@example.com | OtherPass

Views • Views allow you store a query for easy retrieval later. – Query a view as if it were a table – Allows you to name your query – Use views as types – Abstract & encapsulate table structure changes • Allows for easier modification & extension of your database Create basic view CREATE VIEW v_get_all_users AS SELECT * FROM users; Query the view SELECT * FROM v_get_all_users; user_id | email | firstname | lastname | password --------+-------------------+-----------+------------------+-----------+---------------------------- 1 | asnyder@noloh.com | Ash | Snyder | Pass 2 | John | Doe | john@example.com | OtherPass

Views (cont) Alter View CREATE OR REPLACE VIEW v_get_all_users AS SELECT user_id, email, firstname, lastname, password, time_created, to_char(time_created, 'FMMonth FMDDth, YYYY FMHH12:MI:SS AM') as friendly_time FROM users;

Views (cont) – Joined View Finally, lets create a joined view Create companies table CREATE TABLE companies ( "company_id" SERIAL, "company_name" TEXT, PRIMARY KEY("company_id") ); Add company INSERT INTO companies VALUES(DEFAULT, 'NOLOH LLC.'); Add company_id to users ALTER TABLE users ADD COLUMN company_id INTEGER; Update users UPDATE users SET company_id = 1;

Views (cont) – Joined View Alter view CREATE OR REPLACE VIEW v_get_all_users AS SELECT user_id, email, firstname, lastname, password, time_created, to_char(time_created, 'FMMonth FMDDth, YYYY FMHH12:MI:SS AM') as friendly_time, t2.company_id, t2.company_name FROM users t1 LEFT JOIN companies t2 ON (t1.company_id = t2.company_id);

Functions

Functions • Also known as Stored Procedures • Allows you to carry out operations that would normally take several queries and round-trips in a single function within the database • Allows database re-use as other applications can interact directly with your stored procedures instead of a middle- tier or duplicating code • Can be used in other functions • First class citizens – Query functions like tables – Create functions in language of your choice • SQL, PL/pgSQL, C, Python, etc. – Allowed to modify tables and perform multiple operations – Defaults – In/Out parameters

Functions (cont) Create basic function CREATE FUNCTION f_add_company(p_name TEXT) RETURNS INTEGER AS $func$ INSERT INTO companies (company_name) VALUES ($1) RETURNING company_id; $func$ LANGUAGE SQL; Call f_add_company SELECT f_add_company('Google'); f_add_company --------------- 2 (1 row)

Functions (cont) – Syntax Explained • Return type – In this case we used INTEGER • Can be anything you like including your views and own custom types – Can even return an ARRAY of types, such as INTEGER[] • Do not confusing this with returning a SET of types. • Returning multiple rows of a particular types is done through RETURN SETOF. For example, RETURN SETOF v_get_all_users. • $func$ is our delimiter separating the function body. It can be any string you like. For example $body$ instead of $func$. • $1 refers to parameter corresponding to that number. We can also use the parameter name instead. In our example this would be 'p_name'.

Functions (cont) – PL/pgSQL • If you’re using PostgreSQL < 9.0 make sure you add PL/pgSQL support CREATE TRUSTED PROCEDURAL LANGUAGE "plpgsql" HANDLER "plpgsql_call_handler" VALIDATOR "plpgsql_validator";

Functions (cont) – PL/pgSQL CREATE OR REPLACE FUNCTION f_add_company(p_name TEXT) RETURNS INTEGER AS $func$ DECLARE return_var INTEGER; BEGIN SELECT INTO return_var company_id FROM companies WHERE lower(company_name) = lower($1); IF NOT FOUND THEN INSERT INTO companies (company_name) VALUES ($1) RETURNING company_id INTO return_var; END IF; RETURN return_var; END; $func$ LANGUAGE plpgsql;

Functions (cont) Call f_add_company SELECT f_add_company('Zend'); f_add_company --------------- 3 (1 row) Call f_add_company with repeated entry SELECT f_add_company('Google'); f_add_company --------------- 2 (1 row) • We can see that using functions in our database allows us to integrate safeguards and business logic into our functions allowing for increased modularity and re-use.

Triggers

Triggers • Specifies a function to be called BEFORE or AFTER any INSERT, UPDATE, or DELETE operation – Similar to an event handler (but clearly confined) in event based programming – BEFORE triggers fire before the data is actually inserted. – AFTER triggers fire after the statement is executed and data is inserted into the row • Function takes NO parameters and returns type TRIGGER • Most commonly used for logging or validation • Can be defined on entire statement or a per-row basis – Statement level triggers should always return NULL • As of 9.0 can be specified for specific columns and specific WHEN conditions

Triggers (cont) Create logs table CREATE TABLE logs ( "log_id" SERIAL, "log" TEXT, PRIMARY KEY("log_id") ); Create trigger handler CREATE FUNCTION "tr_log_handler"() RETURNS trigger AS $func$ DECLARE log_string TEXT; BEGIN log_string := 'User ' || OLD.user_id || ' changed ' || CURRENT_TIMESTAMP; IF NEW.email != OLD.email THEN log_string := log_string || 'email changed from ' || OLD.email || ' to ' || NEW.email || '. '; END IF; IF NEW.firstname != OLD.firstname THEN log_string := log_string || 'firstname changed from ' || OLD.firstname || ' to ' || NEW.firstname || '. '; END IF; IF NEW.lastname != OLD.lastname THEN log_string := log_string || 'lastname changed from ' || OLD.lastname || ' to ' || NEW.lastname || '. '; END IF; INSERT INTO logs (log) VALUES (log_string); RETURN NEW; END; $func$ LANGUAGE plpgsql;

Triggers (cont) Create trigger CREATE TRIGGER "tr_log" AFTER UPDATE ON users FOR EACH ROW EXECUTE PROCEDURE "tr_log_handler"(); Update user UPDATE users SET firstname = 'Ash' WHERE user_id = 1; Display logs SELECT * FROM logs; log_id | log --------+--------------------------------------------------------------------------------- 1 | User 1 changed 2010-08-30 23:43:23.771347-04 firstname changed from Asher to Ash. (1 row)

Full-Text Search

Full-Text Search • Allows documents to be preprocessed • Search through text to find matches • Sort matches based on relevance – Apply weights to certain attributes to increase/decrease relevance • Faster than LIKE, ILIKE, and LIKE with regular expressions • Define your own dictionaries – Define your own words, synonyms, phrase relationships, word variations

Full-Text Search • tsvector – Vectorized text data • tsquery – Search predicate • Converted to Normalized lexemes – Ex. run, runs, ran and running are forms of the same lexeme • @@ – Match operator

Full-Text Search (cont) Match Test 1 SELECT 'phpbarcelona 2010 is a great conference'::tsvector @@ 'conference & great'::tsquery; ?column? --------- t (1 row) Match Test 2 SELECT 'phpbarcelona 2010 is a great conference' @@ 'conference & bad' ?column? --------- f (1 row)

Full-Text Search (cont) – to_ to_tsvector & plainto_tsquery SELECT to_tsvector('phpbarcelona 2010 is a great conference‘) @@ plainto_tsquery('conference & great') ; ?column? --------- t (1 row) Search through tables SELECT * FROM companies WHERE to_tsvector(company_name) @@ to_tsquery('unlimited'); company_id | company_name ------------+-------------- (0 rows)

Full-Text Search • setweight – Possible weights are A, B, C, D • equivalent 1.0, 0.4, 0.2, 0.1 respectively • ts_rank – Normal ranking function • ts_rank_cd – uses the cover density method of ranking, as specified in Clarke, Cormack, and Tudhope’s “Relevance Ranking for One to Three Term Queries” in the journal, “Information Processing and Management”, 1999.

Full-Text Search (cont) - Ranking setweight & ts_rank_cd SELECT case_id, file_name, ts_rank_cd(setweight(to_tsvector(coalesce(t1.file_name)), 'A') || setweight(to_tsvector(coalesce(t1.contents)), 'B'), query) AS rank FROM cases.cases t1, plainto_tsquery('copyright') query WHERE to_tsvector(file_name || ' ' || contents) @@ query ORDER BY rank DESC LIMIT 10 case_id | file_name | rank ---------+------------------------------------------------------+------ 101 | Harper & Row v Nation Enter 471 US 539.pdf | 84.8 113 | IN Re Literary Works Elec Databases 509 F3d 522.pdf | 76 215 | Lexmark Intl v Static Control 387 F3d 522.pdf | 75.2 283 | Feist Pubs v Rural Tel 499 US 340.pdf | 67.2 216 | Lucks Music Library v Ashcroft 321 F Supp 2d 107.pdf | 59.2 342 | Blue Nile v Ice 478 F Supp 2d 1240.pdf | 50.8 374 | Perfect 10 v Amazon 487 F3d 701.pdf | 43.6 85 | Pillsbury v Milky Way 215 USPQ 124.pdf | 43.6 197 | St Lukes Cataract v Sanderson 573 F3d 1186.pdf | 42 272 | Religious Technology v Netcom 907 F Supp 1361.pdf | 42 (10 rows)

Questions ? Presented by Asher Snyder co-founder of @ashyboy

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Demystifying PostgreSQL

by NOLOH LLC. on Oct 29, 2010

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